The Night Sky Magic of the Atacama

night sky above the atacama

There’s nothing an astronomer – whether professional or amateur – loves more than a clear dark night sky away from the city lights. Outside the glare and glow and cloud cover that most of us experience every day, the night sky comes alive with a life of its own.

Thousands upon countless thousands of glittering jewels – each individual star a pinprick of light set against the velvet-smooth blackness of the deeper void. The arching band of the Milky Way, itself host to billions more stars so far away that we can only see their combined light from our vantage point. The familiar constellations, proudly showing their true character, drawing the eye and the mind to the ancient tales spun about them.

There are few places left in the world to see the sky as our ancestors did; to gaze in wonder at the celestial dome and feel the weight of billions of years of cosmic history hanging above us. Thankfully the International Dark Sky Association is working to preserve what’s left of the true night sky, and they’ve rightfully marked northern Chile to preserve for posterity.

There, the Elqui Valley and the Atacama Desert host night skies impossible to see elsewhere. Away from cities, tucked between the Pacific coast and the high peaks of the Andes, the dry desert air and high elevations make for some of the best observing grounds you can find on Earth.

Paranal Observatory
The ESO’s Paranal Observatory sits proudly above the Atacama desert.

Professional astronomers have taken advantage of this unique climate, constructing massive telescopes and vast arrays on the desolate mountain tops. From the Atacama Large Millimeter/submillimeter Array to the ESO’s Paranal Observatory, Chile is one of the most astronomically productive countries in the world, enabling us to peer into the hearts of galaxies and across the vast reaches of the universe itself.

But the beauty of the Chilean desert sky isn’t reserved solely for professional use. In the past decades specialized resorts have sprung up across the Elqui and Atacama regions, allowing skywatching junkies, enthusiasts, and dreamers to sit in awe under the bowl of the heavens.

I’m personally incredibly passionate about sharing the wonders of astronomy, so that’s why I created AstroTours to let people from around the world experience science for themselves. And as soon as I got the company off the ground, I set my sights squarely on the Atacama.

Alto Atacama open-air observatory
The open-air observatory of the Alto Atacama resort provides a unique stargazing opportunity.

In December 2018 I’m leading a small group to the Atacama, one of the driest places on Earth, so that every night we can sit in the open-air observatories (there’s no need for a dome to block out light pollution here!) and enjoy the night sky in all its splendor. During the day we’ll explore the alien and otherworldly nature of the Atacama itself, from the desiccated salt flats to the relaxing hot springs. It’s all based at the Alto Atacama resort, tucked in the quiet town of San Pedro, Chile.

The trip is designed specifically for an intimate small group, so advance reservations are required. You can find more info and sign up on our Atacama trip page.

A portion of all our proceeds go to help preserve and create dark sky sites like this one. I hope to see you in the Atacama and enjoy together the best night skies we’re likely to see in our lifetimes.

Feature image credit: Gerhard Hüdepohl / atacamaphoto.com.

The Dorado Constellation

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at that fishiest of asterisms – the Dorado constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

Since that time, many additional constellations have been discovered, such as Dorado. This southern constellation, which was discovered in the 16th century by Dutch navigators, is now one of the 88 constellations recognized by the International Astronomical Union (IAU). It is bordered by the constellations of Caelum, Horologium, Hydrus, Mensa, Pictor, Reticulum, and Volans.

Name and Meaning:

Because of its southerly position, Dorado was unknown to the ancient Greeks and Romans so no classical mythological connection exists. However, there are some very nice tales and history associated with this constellation. The name Dorado is Spanish for mahi-mahi, or the dolphin-fish. The mahi-mahi has a opalescent skin that turns blue and gold as the fish dies.

Image of the night sky taken at the European Southern Observatory’s Very Large Telescope in Chile. The Large and Small Magellanic Clouds are visible in the night sky. Credit: ESO, Y. Beletsky

This may very well be the reason Dorado is sometimes called the goldfish is certain stories and legends. Because the early Dutch explorers observed the mahi-mahi chasing swordfish, Dorado was added to their new sky charts following the constellation of the flying fish, Volans. Some very old star atlases refer to Dorado as Xiphias, another form of swordfish, but clearly its “fishy” nature stands!

History of Observation:

Dorado was one of twelve constellations named by Dutch astronomer Petrus Plancius, based on the observations of Dutch sailors that explored the southern hemisphere during the 16th century. It first appeared on a celestial globe published circa 1597-8 in Amsterdam. Dorado was taken a bit more seriously when it was included by Johann Bayer in 1603 in his star atlas, Uranometria, where it appeared under its current name.

It has endured to become one of the 88 modern constellations adopted and approved by the International Astronomical Union.

Notable Objects:

Covering 179 square degrees of sky, it consists of three main stars and contains 14 Bayer/Flamsteed designated stellar members. Dorado has several bright stars and contains no Messier objects. The brightest star in the constellation is Alpha Doradus, a binary star that is approximately 169 light years distant. This binary system is one of the brightest known, and is composed of a blue-white giant (classification A0III) and a blue-white subgiant (B9IV).

The Tarantula Nebula (NGC 2070) located in the southern Dorado constelaltion. Credit: ESO

Beta Doradus, the second brightest star in the constellation, is a Cepheid variable star located approximately 1,050 light years from Earth. Its spectral type varies from white (F-type) to yellow (G-type), like our Sun. Gamma Doradus is another variable, which serves as a prototype for stars known as Gamma Doradus variables, and is approximately 66.2 light years distant.

Another interesting character is HE 0437-5439, an unbound hypervelocity star in Dorado discovered in 2005. This star appears to be receding at the speed of 723 km/s (449 mi/s), and is therefore no longer gravitationally bound to the Milky Way. It is approximately 200,000 light years distant and is a main sequence star belonging to the spectral type BV (a white-blue subdwarf).

Most notable is the Large Magellanic Cloud (LMC), an irregular galaxy located in the constellations Dorado and Mensa. This satellite galaxy to the Milky Way is roughly 1/100 times as massive as our galaxy, with an estimated ten billion times the mass of the Sun. Located about 157,000 light years away, the LMC is home to several impressive objects – like the Tarantula Nebula and the Ghost Head Nebula.

There are no meteor showers associated with the constellation.

The Ghost Head Nebula (NGC 2080), . Credit: ESA/NASA/Mohammad Heydari-Malayeri

Finding Dorado:

The South Ecliptic Pole lies within Dorado and it is bordered by the constellations of Caelum, Horologium, Reticulum, Hydrus, Mensa, Volans and Pictor. It is visible at latitudes between +20° and -90° and is best seen at culmination during the month of January. Let’s begin our explorations with binoculars and Alpha Doradus – the “a” symbol on our map. One of the reasons this star shines so brightly is because it’s not one – but two.

Don’t get your telescope out just yet, because Alpha is separated by only only a couple tenths of a second of arc and both members are about a magnitude apart. Located about 175 light years away from our solar system, this tight pair averages a distance between each other that’s equal to about the same distance as Saturn from our Sun. That’s not particularly unusual for a binary star, but what is unusual is the primary star. Alpha Dor A’s spectrum is “peculiar” – very rich in silicon. It seems to be concentrated in a stellar magnetic spot!

Let’s have a look at Cephid variable star Beta Doradus – the “B” symbol on our map. Beta is an evolved super giant star and every 9.942 days it reaches a maximum brightness of magnitude 3.46 then drops to magnitude 4.08. While these types of changes are so slight they would be difficult to follow with just the eye, that doesn’t mean what happens isn’t important. By studying Cephids we understand “period-luminosity” relation. The pulsation period of a Cepheid gives us absolute brightness, and comparing it with apparent brightness gives us distance. That way, when we find a Cepheid variable star in another galaxy, we can tell just how far away that galaxy is!

Now, let’s go from one end of the constellation to the other with binoculars as we start with Delta Doradus – the “8” shape on our map. If you were on the Moon, this particular star would be the south “pole star” – just like Polaris is to the north on Earth! Sweep along the body of the fish and end at Gamma Doradus – the “Y” shape on our map. Guess what? Another variable star! But this one isn’t a Cepheid. Gamma Doradus variables are variable stars which display variations in luminosity due to non-radial pulsations of their surface.

The stars are typically young, early F or late A type main sequence stars, and typical brightness fluctuations are 0.1 magnitudes with periods on the order of one day. This is a relatively new class of variable stars, having been first characterised in the second half of the 1990s, and details on the underlying physical cause of the variations remains under investigation. We call these mysterious strangers Oscillating Blue Stragglers.

Don’t put away your binoculars yet. We have to look at R Doradus! Here we have a red giant Mira variable star that’s about 200 to 225 light years away from Earth. The visible magnitude of R Doradus varies between 4.8 and 6.6, which makes the variable changes easy to follow with binoculars, but when viewed in the infrared it is one of the brightest stars in the sky. However, this isn’t what the most interesting part is.

With the exception of our own Sun, R Doradus is currently believed to be the star with the largest apparent size as viewed from Earth. The stellar diameter of R Doradus could be as much as 585 million kilometers. That’s upwards to 400 times larger than Sol – yet it has about the same mass! If placed at the center of the Solar System, the orbit of Mars would be entirely contained within the star. Too cool…

Dorado contains a huge amount of deep sky objects very well suited for binoculars, small and large telescopes. So many, in fact, our small star chart would be so cluttered that it would be impossible to read designations. One of the most notable of all is the Large Magellanic Cloud, one of our Milky Way Galaxy’s neighbors and members of our local galaxy group. In itself, it is an irregular dwarf galaxy, distorted by tidal interaction with the Milky Way and may have once been barred spiral galaxies.

The Magellanic Clouds’ radial velocity and proper velocity were recently accurately measured by a team from the Harvard-Smithsonian Center for Astrophysics to produce a 3-D velocity measurement that clocked their passage through the Milky Way galaxy in excess of 480km/s (300 miles per second) using input from Hubble Telescope. This unusually high velocity seems to imply that they are in fact not bound to the Milky Way, and many of the presumed effects of the Magellanic Clouds have to be revised. Be sure to explore the LMC for its own host of nebula and star forming regions. It was host to a supernova (SN 1987A), the brightest observed in over three centuries!

For the telescope, there are many objects in Dorado that you don’t want to miss. (This article would be 10 pages long if I listed them all, so let’s just highlight a few.) For galaxy group fans, why not choose NGC 1566 (RA 04h 20m 00s Dec -56 56.3′) NGC 1566 is a spiral galaxy that dominates the Dorado Group and it is also a Seyfert galaxy as well. At the center of the cluster, look for interacting galaxies NGC 1549 and NGC 1553.

These two bright members are lenticular galaxy NGC 1553 (RA 04h 16m 10.5s Dec -55 46′ 49″), and elliptical galaxy NGC 1549 (RA 04h 15m 45.1s Dec -55 35′ 32″). Their interaction appears to be in the early stage and can be seen in optical wavelengths by faint but distinct irregular shells of emission and a curious jet on the northwest side. Chandra X-ray imaging of NGC 1553 show diffuse hot gas making up 70% of the emissions, dotted with many point-like sources (low-mass X-ray binaries) making up the rest.

Similar to Messier 60, these bright spots are binary star systems of black holes and neutron stars most of which are located in globular clusters and reflect this old galaxy’s very active past. In these systems, material pulled off a regular star is heated and gives off X-rays as it falls toward the accompanying black hole or neutron star.

The location of the southern Constellation Dorado. Credit: IAU/Sky&Telescope magazine

 

Turn your telescope towards NGC 2164 (RA 05h 58m 53s Dec -68 30.9′). Here we are resolving an open star cluster / globular cluster that’s in another galaxy, folks! Also nearby you’ll find faint open cluster NGC 2172 (RA 5 : 59.9 Dec -68 : 38) and galactic star cluster NGC 2159 (05 57.8, -68 38). What a treat to study in another galaxy!

Would you like to study another complex? Then let’s take a look at NGC 2032 (RA 05h 35m 21s Dec -67 34.1′). Better known as the “Seagull Nebula” this complex that contains four separate NGC designations: NGC 2029, NGC 2032, NGC 2035 and NGC 2040. Spanning across an open star cluster, there are many nebula types here including emission nebula, reflection nebula and HII regions. It is also bissected by a dark nebula, too!

Of course, no telescope trip through Dorado would be complete without stopping by NGC 2070 (RA 05h 38m 37s Dec -69 05.7′) – the “Tarantula Nebula”. Located about 180,000 light years from our solar system and first recorded by Nicolas Louis de Lacaille in 1751, this huge HII region is an extremely luminous object. Its luminosity is so bright that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in our Local Group of galaxies! At its core lies the extremely compact cluster of stars that provides the energy to make the nebula visible. And we’re glad it does!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

The Crux Constellation

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at the “Southern Cross” – the Crux constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

One of these constellations is known as Crux, a small constellation located in the southern skies. Despite its size, it is one of the most well-known constellations in the southern hemisphere due to its distinctive cross-shape. Today, it has gone on to become one of the 88 modern constellations currently recognized by the International Astronomical Union (IAU).

Name and Meaning:

For the people of the Southern Hemisphere, the Crux constellation has a great deal of cultural significance. The Incas knew the constellation as Chakana (Quechua for “the stair”), and a stone image of the stars was found in Machu Picchu, Peru. To the Maori, the constellation was known as Te Punga, or “the anchor”, due to the important role it played in maritime navigation.

The “Emu in the Sky”, an important constellation recognized by the Aborigines of Australia. Credit: RSAA/ANU

To the Aborigines of Australia, the cross and the Coalsack Nebula together represented the head of the Emu in the Sky. This mythical bird is associated with several Aborigine creation myths and is one of the most important constellations in their astronomical traditions. Because of this significance, the Southern Cross is represented on the flags of Australia, Papua New Guinea, New Zealand Brazil, and Brazil.

The first recorded instance of Crux being named is believed to have occurred in 1455, when Venetian navigator Alvise Cadamosto made note of an asterism in the southern skies that he called carr dell’ostro (“southern chariot”). However, historians generally credit Portugese astronomer Joao Faras with the discovery, which occurred in 1500 when he spotted it from Brazil and named it “Las Guardas” (“the guards”).

By the late 16th century, Crux began to be depicted as a separate constellation on celestial globes and maps. In these and subsequent maps, the name Crux was used (Latin for “Cross”), referring to the constellation’s distinct shape.

History of Observation:

Crux was originally considered to be part of Centaurus, but as the precession of the equinoxes gradually lowered these stars below the European horizon, they were lost sight of, and so was the memory of these stars. At one time, around 1000 BCE, the stars of Crux were visible to the northern hemisphere, but by 400 CE they had slipped below the horizon for most populated areas.

The constellation Crux as it can be seen by the naked eye. Credit: Till Credner/AlltheSky.com

Even though it was originally plotted on Ptolemy’s Almagest, it first appeared as “Crux” on the charts of Petrus Plancius and Jodocus Hondius in 1598 and 1600 – both navigators. It is known that Amerigo Vespucci mapped the stars of Crux on his expedition to South America in 1501, and with good reason!

Two of the stars of Crux (Alpha and Gamma, Acrux and Gacrux respectively) are commonly used to mark due south. Following the line defined by the two stars for approximately 4.5 times the distance between them leads to a point close to the Southern Celestial Pole. A definite point needed for navigation! In 1920, Crux was included among the 88 modern constellations recognized by the IAU.

Notable Objects:

Of the major stars in Crux, Alpha Crucis (Acrux) is the brightest, and the 12th brightest star in the night sky. It is located approximately 320 light years away and is a multiple star system composed of Alpha-1 Crucis (a B class subgiant) and Alpha-2 Crucis (a B class dwarf). Both stars are very hot and their respective luminosities are 25,000 and 16,000 times that of the Sun.

Beta Crucis (Becrux, or Mimosa) is the second brightest star of the Southern Cross and the 20th brightest star in the night sky. It is approximately 350 light years distant, is classified as a Beta Cephei variable, and is a spectroscopic binary composed of two stars that are about 8 AU apart and orbit each other every five years. The name Mimosa refers to its color (blue-hued).

Gamma Crucis (Gacrux) is a red giant that is approximately 88 light years distant from Earth. It is the third brightest star in the Crux constellation and the 26th brightest star in the sky. Located about 400 light years distant from Earth, this binary star is composed of a M4 red dwarf star and a A3 white dwarf star.

Crux is also associated with several Deep Sky Objects, the most notable of which is the Coalsack Nebula. This object is easily seen as a dark patch in the southern region of the Milky Way (hence the name) and crosses into the neighboring constellations of Centaurus and Musca. It is located about 600 light years from Earth and is between 30 and 35 light years in radius. In Aboriginal astronomy, the nebula represents the head of the Emu.

Then there’s the Kappa Crucis Cluster (aka. the “Jewel Box” or “Herschel’s Jewel Box”), an open star cluster that is located approximately 6,440 light years from Earth. It contains roughly 100 stars and is one of the youngest clusters ever discovered (only 14 million years old). To the naked eye, the cluster appears like a star near Beta Crucis.

Finding Crux:

The constellation itself consists of four bright, main stars and 19 stars which have Bayer/Flamsteed designations. It is bordered by the constellations of Centaurus and Musca. At present, Crux is visible at latitudes between +20° and -90°. While it is fairly circumpolar for the southern hemisphere, it is best seen a culmination during the month of May.

The location of the Crux constellation. Credit: IAU

Now, let’s take out binoculars and examine its stars, started with Alpha Crucis, the “a” shape on our map. Its proper name is Acrux and it is the twelfth brightest star in the night sky. If you switch your binoculars out for a telescope, you’ll find that 321 light year distant Acrux is also a binary star, with components separated by about 4 arc seconds and around one half stellar magnitude difference in brightness.

The brighter of the two, A1 is itself a spectroscopic binary star – with a companion that orbits no further away than our own Earth, yet is around 14 times larger than our own Sun! Needless to say, there’s a very good chance this star may one day go supernova. While you’re there, take a look an addition 90 arc seconds away for a third star. While it may just be an optical companion to the Acrux system, it does share the same proper motion!

Back to binoculars an on to Beta Crucis – the “B” shape on the map. Mimosa is located about 353 light years away from our solar system and it is also a spectroscopic binary star. This magnificent blue/white giant star is tied at number 19 as one of the brightest stars in the sky, and if we could put it side by side with our Sun it would be 3000 times brighter. Mimosa is also a multiply-periodic Beta-Cephi type star, too, fluxing by about 1/10 of a magnitude in as little as hours. What’s going on? Inside Beta Crucis the iron content is only about half that of Sol and it’s nearing the end of its hydrogen-fusing stage. When the iron core develops? Watch out! It’s supernova time….

Now hang on to your binoculars and head north for Gamma Crucis, the “Y” shape on the map. Gacrux, is a red giant star approximately 88 light-years away from Earth. Did you notice its optical companion about 2 arc minutes away at an angle of 128 degrees from the main star? While the two look close together in the sky, the secondary star is actually 400 light years away! Gacrux shows its beautiful orange coloring to prove it has evolved off of the main sequence to become a red giant star, and it may even be evolving past the helium-burning stage.

The Coalsack Nebula and Kappa Crucis Cluster. Credit: A. Fujii

Move on now to Delta Crucis – the figure “8” on our map. Decrux is a red giant star located about 360 light years away from our vantage point. Delta Crucis is also Beta Cephei variable and changes its brightness just a tiny bit over a period of about an hour and 20 minutes. Another cool factoid about Delta Crucis is that it’s a fast rotator – spinning at a speed of at least 194 kilometers per second at the equator and making a full rotation in about 32 hours.

This massive star also produces a massive stellar wind, shooting off 1000 times more material than our own Sun every second of every day! Or try R Crucis… It’s also a Beta-Cephi type variable star, but it changes by nearly a full stellar magnitude in just a little over five days!

Keep your binoculars handy and head back to Beta and sweep south a degree and a half for the Kappa Crucis star cluster. This beautiful galactic cluster of stars commonly known as the Jewel Box (NGC 4755). After you see its glittering collection of multi-colored stars, you’ll understand how it got its name! It is one of the youngest clusters, perhaps only a few million years old.

Kappa Crucis is also right on the edge of a dark void in the sky called the “Coal Sack”. While you’re looking around, you’ll notice that there seem to be very few stars in this area. That’s because they are being blocked by a dark nebula! The Coal Sack is a large, dark dust cloud about 500 light years away and it’s blocking out the light from stars which lie beyond it. The few stars you do see are in front of the cloud and much nearer to the Earth.

The Jewel Box – the Kappa Crucis Cluster. Credit: ESO/NASA/ESA/Digitized Sky Survey 2/Jesús Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)

Now it’s telescope time. Head to Alpha Crucis and slightly less than 2 degrees east for NGC4609. Also on the edge of the Coalsack, this large, fairly condensed open cluster contains about 40 members and they are well spread across the sky. The pattern somewhat resembles the constellation of Orion (in the imagination, of course!). Mark you observing notes for Caldwell 98. Next stop? Back to Delta and less than 3 degrees south/southwest for NGC4103, another open cluster on the edge of night. With a little bit of imagination, this grouping of stars could appear to look like a celestial water tower!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

The Crater Constellation

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at “The Cup” – the Crater constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age

One of these constellation is Crater (aka. “The Cup”), an asterism located in the Southern Hemisphere. This small constellation is located south of the ecliptic plane, with no bright marker stars. As part of the Hercules family, it is bordered by the constellations of Leo, Sextans, Hydra, Corvus and Virgo. Today, it is one of the 88 modern constellations recognized by the International Astronomical Union.

Name and Meaning:

In Greek mythology, Crater represents the Cup of Apollo – the god of the skies – which is due to its chalice-like configuration. The cup is being held up by the Raven – Corvus – another figure in Greek mythology. The tale, much like many mythological stories, is a sad one, and begins with the Raven being sent to fetch water for his master, Apollo.

Unfortunately, Corvus (the Raven) was distracted as he became tempted by a fig, and then waited too long for it to ripen. When he realized his mistake, he returned sorrowfully to Apollo with his cup (Crater) and brought along the serpent Hydra in his claws as well. Angry, Apollo tossed all three into the sky for all eternity, where they became part of the starry firmament.

Corvus, Crater and other constellations seen around Hydra. From Urania's Mirror (1825). Credit: US Library of Congress
Corvus, Crater and other constellations seen around Hydra. From Urania’s Mirror (1825). Credit: US Library of Congress

History of Observation:

The Crater constellation comes to us from Classical Antiquity and was recorded by Ptolemy in his 2nd-century CE tract the Almagest. However, it was also recognized by Chinese astronomers, where the stars associated with it were viewed as being part the Vermillion Bird of the South (Nan Fang Zhu Que). Along with the some of the stars from Hydra, they depict the Red Bird’s wings.

Notable Objects:

Crater has only a few bright stars associated with it and no Messier Objects. The brightest, Delta Crateris, is an orange giant located approximately 196 light yeas from Earth. The star is also known as Labrum (Latin for “the lip”), due to the fact that it was sometimes associated with the story of the Holy Grail.

Next is Alpha Crateris, an orange giant located approximately 174 light-years from Earth which is 80 times more luminous than our Sun. It is also known as Alkes, derived from the Arabic word alkas, which means “the cup”. Then there’s Beta Crateris, a white sub-giant that is located approximately 266 light years from Earth. This star is also known by the name Al Sharasif, which means “the ribs” in Arabic.

In terms of Deep Sky Objects, Crater has no associated Messier Objects, but a few galaxies can be found in its region of the night sky. These include the Crater 2 dwarf galaxy, a satellite galaxy of the Milky Way that is located approximately 380,000 light years from Earth. There’s also the spiral galaxy known as NGC 3511, which has a slight bar and is seen from Earth nearly edge-on.

The spiral galaxy NGC 3887, located in the constellation Crater. Credit: NASA (Wikisky)

There’s also the NGC 3887 and NGC 2981 spiral galaxies, and the RX J1131 quasar, which is located 6 billion light years away from Earth. Interestingly, the black hole at the center of this quasar was the first to have its spin directly measured by astronomers.

Finding Crater:

Crater is visible at latitudes between +65° and -90° and is best seen at culmination during the month of April. It is comprised of only 4 main stars, and 12 stars with Bayer/Flamsteed designations. In order to spot these stars, observers should begin by looking for the Alpha star (the “a” shape on their star map) with binoculars.

Situated some 174 light-years from Earth, Alpha Crateris (the star’s official designation) is a spectral class K1 star – an orange giant that’s a little different from the rest. This is because Alkes is a “high velocity” star, which means it moves far faster than the stars around it. Another thing that sets it apart is its high metal content, which according to some researchers, it may have picked up when it came from the inner, metal-rich part of the Galaxy.

Artist's impression of Alkes - aka. Alpha Crateris. Credit: constellation-guide.com
Artist’s impression of Alkes – aka. Alpha Crateris – a K1 orange giant star in the Crater constellation. Credit: constellation-guide.com

Next, observers should look to Beta Crateris (the “B” shape on the map) which also goes by the name of Al Sharasif. This star is not an ordinary one either. For starters, Al Sharasif is about 265 light-years from our solar system, and it’s a white sub-giant star. To boot, it also has a low mass, white dwarf companion – which is why astronomers classify it as a Sirius-like system.

Next up is Delta Crateris – the “8” symbol on the map – which is an orange giant, spectral class K0III star with an apparent magnitude of 3.56. In time, this star will become an even larger giant, eventually turning into a Mira-type variable star before ending its life as a white dwarf. Oddly enough, Labrum has a very low metal content compared to its Crater-neighbors, containing about 40% as much iron as our own Sun.

At this point, observers with telescopes and have a look at Gamma Crateris – the “Y” shape on the map. Gamma Crateris is a fixed binary white dwarf star with an easy separation of 5.2″. Gamma itself is 89 light-years for Earth, which is rather hard to believe when you try to seek out the 9.5 stellar magnitude companion that accompanies it.

Although this is a disparate double star, it is still quite fun and easy to spot with a small telescope. For a challenge, try Iota Crateris – a close binary star with an 11th magnitude companion that’s only separated by 1.4″. Psi Crateris is an even closer binary. Both stars are within a half magnitude of each other, but the separation is only 0.2″.

Artist's impression of white dwarf binary pair CSS 41177. Image: Andrew Taylor.
Artist’s impression of white dwarf binary pair, a type of star system that describes Gamma Crateris. Credit: Andrew Taylor.

Next up is R Crateris, a variable star that can be observed with binoculars, and which is located at RA 10 56 Dec -17 47. You will notice it by its lovely red color and its nice change of magnitude, which goes from 8 to 9.5 in a period of about 160 days. And then there’s SZ Crateris, a magnitude 8.1 variable star. It is a nearby star system located about 44 light years from the Sun and is known as Gliese 425 – which in the past was known as Abt’s Star.

While there’s no brighter deep sky objects for binoculars or small telescopes, there are a couple of challenging galaxies in the Crater constellation that are well suited to a large aperture. Let’s start with the brightest – elliptical galaxy NGC 3962 – which is easy to spot (like all elliptical galaxies), though there’s not much detail to be seen. Even if it is not terribly exciting to behold, it is on the Herschel 400 observing list.

And then there’s NGC 3887 (11h47.1 -16 51), a nice spiral galaxy that’s only slightly fainter. It has two faint stars which accompany it and a stellar nucleus which occasionally makes an appearance and provides an opportunity for some very interesting viewing. Both of these galaxies are in the slightly fainter range, both being just under magnitude 11.

Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
List of the stars that appear in the Crater constellation. Credit: IAU and Sky & Telescope magazine/Roger Sinnott & Rick Fienberg

Observers who are skilled with telescopes should also keep and eye out for NGC 3511 (11h03.4 -23 05), a spiral galaxy of magnitude 11.5. It is joined in the same field of view by NGC 3513, a barred spiral galaxy that is a full magnitude dimmer. People with larger telescopes should also take a crack at spotting NGC 3672 (11h25.0 -09 48), a faint spiral galaxy that nevertheless has nice halo and a bright, apparent nucleus.

And last, but not least, there is NGC 3981 (11h56.1 -19 54), a beautifully inclined, magnitude 12 spiral galaxy that has a bright nucleus, and which sometimes shows some spiral galaxy structure when observing conditions are right.

Drink up… the “Cup” is waiting!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

The Corvus Constellation

Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at the “Raven” – the Corvus constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

One of these constellation is the Corvus constellation, a southern constellation whose name in Latin means “the Raven”. Bordered by the constellations of Virgo, Crater and Hydra, it is visible at latitudes between +60° and -90° and is best seen at culmination during the month of May. Today, it is one of the 88 modern constellations recognized by the International Astronomical Union (IAU).

Name and Meaning:

In classical mythology, Corvus represents the Raven, and is both a charming and sad tale. Legend tells us that the constellation of Crater is the cup of the gods. This cup belonged to the god of the skies himself, the venerable archer-god Apollo. And who holds this cup, dressed in black? The Raven, Corvus.

“Noctua, Corvus, Crater, Sextans Uraniæ, Hydra, Felis, Lupus, Centaurus, Antlia Pneumatica, Argo Navis, and Pyxis Nautica”, plate 32 in Urania’s Mirror, by Sidney Hall. Credit: Library of Congress

The story of a creature sent to fetch water for his master, only to stop to eat figs. Corvus tarried too long, waiting on a fig to ripen. When he realized his mistake, the Raven returned to Apollo with his cup and brought along the serpent Hydra in his claws as well, claiming that the snake prevented him from filling the cup.

Realizing his feathered-friend’s lie, Apollo became angry and tossed the cup (Crater), the snake (Hydra) and the raven (Corvus) into the sky, where they became constellations for all eternity. He further punished the raven by making sure the cup would be out of reach, thus ensuring he would forever be thirsty.

History of Observation:

As with most of the 48 constellations recorded by Ptolemy, the Corvus constellation has roots that go back to ancient Mesopotamia. In the Babylonian star catalogues (dated to ca. 1100 BCE), Corvus was called the Babylonian Raven (MUL.UGA.MUSHEN), which sat on the tail of the Serpent – which was associated with Ningishzida, the Babylonian god of the underworld. This constellation was also sacred to the god of rains and storm (Adad).

By about 500 BCE, this constellation was introduced to the Greeks, along with Crater, Hydra, Aquila and Piscis Austrinus constellations. By the 2nd century CE, they were included by Ptolemy in his Almagest, which would remain the definitive source on astronomy and astrology to Medieval European and Islamic astronomers for many centuries.

In Chinese astronomy, the stars that make up Corvus are located within the Vermilion Bird of the South (Nán Fang Zhu Què). The four main stars depict a chariot (Zhen) while Alpha and Eta mark the linchpins for the wheels, and Zeta represents a coffin (Changsha).

In Indian astronomy, the first five stars in Corvus correspond to the Hast nakshatra – a lunar zodiacal constellation. This is one of is one of the 27 or 28 divisions of the sky, identified by the prominent stars in them, that the Moon passes through during its monthly cycle. While it is Hindu, it is still very similar to the divisions of the ecliptic plane referred to as the zodiac. The Moon takes approximately one day to pass through each nakshatra.

Notable Objects:

This small, box-like asterism has no bright star and consists of 11 stars which are visible to the unaided eye, yet Ptolemy only listed 7! There are 4 main stars and 10 which have Bayer/Flamsteed designations. For unaided eye observers, the Delta, Gamma, Epsilon and Beta (what appears to look like a figure 8, Y, E and B on the map) form an asterism that looks like a “sail”, and when connected seem to point to the bright star Spica.

The brightest star in Corvus is not even its alpha, but is Gamma Corvi. This giant star (which is thought to be a binary system) is located approximately 165 light years from Earth and is also known as Gienah, which comes from the Arabic phrase al-janah al-ghirab al-yaman (“the right wing of the crow”).

Antennae Galaxies – NGC 4038, NGC 4039. Credit: NASA, ESA, and the Hubble Heritage Team (STScI, AURA)-ESA, Hubble Collaboration

The second-brightest star, Beta Corvi, is a yellow-white G-type bright giant that is located about 140 light years from Earth. Its proper name, Kraz, was assigned to it in modern times, but the origin of the name is uncertain. Delta Corvi is a class A0 star in Corvus located approximately 87 light years distant from Earth whose traditional name (Algorab) comes from the Arabic word al-ghuraab – which means “the crow.”

Epsilon Corvi is a K2 III class star that is approximately 303 light-years from Earth. The star’s traditional name, (Minkar) comes from the Arabic word almánxar, which means “the nostril of the crow.” Alpha Corvi, which is only the fifth brightest star in the constellation, is a class F0 dwarf or subdwarf that is only 48.2 light years distant. The star’s traditional name (Alchiba) is derived from the Arabic al hibaa, which means “tent.”

Corvus is also home to many Deep Sky Objects. These include the Antennae Galaxies (NGC 4038/NGC 4039), a pair of interacting galaxies that were first discovered in the late 18th century. These colliding galaxies – which are located 45 million light years from Earth – are currently in the starburst stage, meaning they are experiencing an exceptionally high rate of star forming activity.

There’s also the NGC 4027 barred spiral galaxy, which is located about 83 million light years from Earth. This galaxy is peculiar, in that one of its spiral arm extends further than the other – possibly due to a past collision with another galaxy. Finally, there’s the large planetary nebula known as NGC 4361, which is located at the center of the constellation and resembled a faint elliptical galaxy.

The barred, spiral galaxy known as NGC 4027. Credit : ESO

Finding Corvus:

Let’s start with binoculars and look down at the southern corner, where we will find Alpha Corvi – aka. Alchiba. Alchiba belongs to the spectral class F0 and has apparent magnitude +4.00. This star is suspected of being a spectroscopic binary, although this has not yet been confirmed. Now take a look at Beta Corvi – aka. Kraz. Good old Kraz is approximately 140 light-years away and is a G-type bright giant star whose apparent visual magnitude varies between 2.60 and 2.66.

Head west and look at Epsilon. Although it doesn’t look any further away, spectral class K2 III – Minkar – is 303 light-years from Earth! Need a smile? Then take a look at Gamma, aka. Geinah. How about Delta? Algorab is a spectral class A0 and is about 87 light years from our solar system.

Now get out your telescope as we explore planetary nebula, NGC 4361 (RA 12 24 5 Dec -18 48). At around magnitude 10, this greenish disc is fairly easily spotted with smaller telescopes, but the 13th stellar magnitude central star requires larger aperture to be seen. It has a very symmetrical shape that is similar to a spiral galaxy.

For galaxy fans, have a look at interacting galaxy pair, NGC 4038 and NGC 4039 – the “Ringtail Galaxy” (RA 12 01 53 Dec -18 52-3). This peculiar galaxy (also referred to as the “Antennae Galaxies”) were both discovered by Friedrich Wilhelm Herschel in 1785. Even in relatively small telescopes, you can see two long tails of stars, gas and dust thrown out of the galaxies as a result of the collision that resemble the antennae of an insect.

Map of the Corvus Constellation. Credit: IAU and Sky&Telescope magazine

As explained by Vázquez (et al.) in a 1999 study:

“The morphology of this object is complex given the highly filamentary structure of the envelope, which is confirmed to possess a low mass. The halo has a high expansion velocity that yields incompatible kinematic and evolutionary ages, unless previous acceleration of the nebular expansion is considered. However, the most remarkable result from the present observations is the detection of a bipolar outflow in NGC 4361, which is unexpected in a PN with a Population II low-mass-core progenitor. It is shown that shocks resulting from the interaction of the bipolar outflow with the outer shell are able to provide an additional heating source in this nebula.”

Most galaxies probably undergo at least one significant collision in their lifetimes. This is likely the future of our Milky Way when it collides with the Andromeda Galaxy. Two supernovae have been discovered in the galaxy: SN 2004GT and SN 2007sr. A recent study finds that these interacting galaxies are closer to the Milky Way than previously thought – at 45 million light-years instead of 65 million light-years. Geez… What’s 20 million light years between friends?

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

The Corona Australis Constellation

Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with the “Southern Crown” – the Corona Australis constellation!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

One of these was the Coronoa Australis constellation, otherwise known as the “Southern Crown”.  This small, southern constellation is one of the faintest in the night sky, where it is bordered by the constellations of Sagittarius, Scorpius, Ara and Telescopium. Today, it is one of the 88 modern constellations recognized by the International Astronomical Union.

Name and Meaning:

Corona Australis – the “Southern Crown” – is the counterpart to Corona Borealis – the “Northern Crown”. To the ancient Greeks, this constellation wasn’t seen as a crown, but a laurel wreath. According to some myths, Dionysus was supposed to have placed a wreath of myrtle as a gift to his dead mother into the underworld as well. Either way, this small circlet of dim stars definitely has the appearance of a wreath – or crown – and belongs to legend!

False-colour image from the ESO’s Very Large Telescope of the star-forming region NGC 6729. Credit: ESO

History of Observation:

Like many of the Greek constellations, it is believed that Corona Australis was recorded by the ancient Mesopotamian in the MUL.APIN – where it may have been called MA.GUR (“The Bark”). While recorded by the Greeks as early as the 3rd century BCE, it was not until Ptolemy’s time (2nd century CE) that it was recorded as the “Southern Wreath”, a name that has stuck ever since.

In Chinese astronomy, the stars of Corona Australis are located within the Black Tortoise of the North and were known as ti’en pieh (“Heavenly Turtle”). During the Western Zhou period, the constellation marked the beginning of winter. To medieval Islamic astronomers, Corona Australis was known alternately as Al Kubbah (“the Tortoise”), Al Hiba (“the Tent”) or Al Udha al Na’am (“the Ostrich Nest”).

In 1920, the constellation was included in the list of 88 constellations formally recognized by the IAU.

Notable Objects:

Corona Australis is a small, faint constellation that has no bright stars, consists of 6 primary stars and contains 14 stellar members with Bayer/Flamsteed designations. There is one meteor shower associated with Corona Australis – the Corona-Australids which peak on or about March 16 each year and are active between March 14th through the 18th. The fall rate is minimal, with an average of about 5 to 7 per hour.

It’s brightest star, Alpha Coronae Australis (Alphekka Meridiana), is a class A2V star located about 130 light years from Earth. It is also the only properly-named star in the constellation. It’s second brightest star, Beta Coronae Australis, is a K-type bright giant located approximately 510 light years distant.

And then there’s R Coronae Australis, a well-known variable star that is located approximately 26.8 light years from Earth. This relatively young star is still in the process of formation – accreting material onto its surface from a circumstellar disk – and is located within a star forming region of dust and gas known as NGC 6726/27/29.

Corona Australis is also home to several Deep Sky Objects, such as the Corona Australis Nebula. This bright reflection nebula, which is located about 420 light years away, was formed when several bright stars became entangled with a dark cloud of dust. The cloud is a star-forming region, with clusters of young stars embedded inside, and consists of three nebulous regions – NGC 6726, NGC 6727, and NGC 6729.

Other reflection nebulas include NGC 6726/6727 and the fan-shaped NGC 6729. Corona Australis also boasts many star clusters, such as the large, bright globular cluster known as NGC 6541. There’s also the Coronet cluster, a small open star cluster that is located approximately 420 light years from Earth. The cluster lies at the heart of the constellation and is one of the nearest known regions that experiences ongoing star formation.

Color image of the Coronet Australis Nebula, taken by NASA’s WISE (Wide-field Infrared Survey Explorer). Credit: NASA/Caltech

Finding Corona Australis:

Corona Australis is visible at latitudes between +40° and -90° and is best seen at culmination during the month of August. It can be explored using both binoculars and small telescopes. Let’s start with binoculars and a look at Alpha Coronae Australis – the only star in the constellation to have a proper name.

Called Alfecca Meridiana – or “the sixth star in the river Turtle” – Alpha is a spectral class A2V star which is located about 160 light years from Earth. Alfecca Meridiana is a fast rotator, spinning at least at 180 kilometers per second at its equator, 90 times faster than our Sun and making a full rotation in about 18 hours.

Even more interesting is the fact that Alpha is a Vega-like star, pouring out excess infrared radiation that appears to be coming from a surrounding disk of cool dust. Just what does that mean? It means that Alfecca Meridiana could possibly have a planetary system!

Now have a look at Beta. Although this orange class K (K0) giant star is rather ordinary, where it’s at is not. It’s sitting on the edge of the Corona Australis Molecular Cloud, a dusty, dark star-forming region which contains huge amounts of nebulae. While Beta does seem pretty plain, it is almost 5 times larger than our Sun and 730 times brighter. Not bad for a star that’s about a hundred million years old!

Image of the globular cluster NGC 6541 in Corona Australis, based on observations made with the NASA/ESA Hubble Space Telescope. Credit: STScI/NASA/ST-ECF/ESA/CADC/NRC/CSA.

Now, take a look at a really bizarre star – Epsilon Coronae Australis. At a distance of 98 light years, there doesn’t seem to be much going on with this fifth magnitude, faint stellar point, but there is. That’s because Epsilon isn’t one star – but two. Epsilon is an eclipsing binary with two very similar eclipses that take place within an orbital period of 0.5914264 days, as first a faint star passes in front of the bright one that gives us 95 or so percent of the light, and then the bright one passes in front of the fainter.

So what does that mean? It means that if you sit right there at watch, you can see the changes in less than 7 hours. While watching for hours for a half magnitude drop might not seem like your cup of tea, think about what you’re watching…. These two stars are actually contacting each other as they go by! Can you imagine stars spinning so fast that they produce huge amounts of magnetic activity and dark starspots that also add to the variation as they swing in and out of view? Sharing mass and pulling at each other in just a matter of hours? Now that’s a show worth watching…

Now try variable star R Coronae Borealis (RA 19 53 65 Dec -36 57 97). Here we have another unusual one – a “Herbig Ae/Be” pre-main sequence star. The star is an irregular variable with more frequent outbursts during times of greater average brightness, but it also has a long-term periodic variation of about 1,500 days and about 1/2 magnitude that may be linked to changes in its circumstellar shell, rather than to stellar pulsations. Although R Coronae Australis is 40 times brighter than Sol, and about 2 to 10 times larger, most of its stellar luminosity is obscured because the star is still accreting matter. Protoplanetary bodies? Maybe!

Keep your binoculars handy and get out the telescope as we start deep sky first with NGC 6541. Also known as Caldwell 78 and Bennett 104, this beautiful 6th magnitude globular cluster was first discovered by N. Cacciatore on March 19, 1826. It belongs in our Milky Way galaxy’s inner halo structure and it is rather metal poor in structure – but beautifully resolved in a telescope. In binoculars, this splendid southern sky study will appear as a large faint globular with a bright star to the northeast.

The location of the southern constellation of Corona Astralis. Credit: IAU/ Sky&Telescope magazine

Now head for the telescope and NGC 6496 (RA 17 59 0 Dec -44 16). At right around magnitude 9, this globular cluster also has a bonus nebula attached to it. Collectively known as Bennett 100, Dreyer described it as a “nebula plus cluster” but it will take dark skies to make out both. Look for 5th magnitude star SAO 228562 that accompanies it. In a small telescope, only a hazy, faint patch can be seen, but larger aperture does get some resolution.

Try emission/reflection nebula NGC 6729 (RA 19 01 55 Dec -36 57 30) next. In a wide field, you can place NGC 6726, NGC 6727, NGC 6729 and the double star BSO 14 in the same eyepiece. The three nebulae NGC 6726-27, and NGC 6729 were discovered by Johann Friedrich Julius Schmidt, during his observations at Athen Observatory in 1861. The nebula are very faint and almost comet-like in appearance and the double star is easily split. Don’t forget to mark your notes as having captured Caldwell 68!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

The Columba Constellation

Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with the dove – the Columba constellation!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

Since then, thanks to the efforts of astronomer and explorers, many more constellations have come to be recognized. One of these is the constellation Columba (also known as “the dove”), which was discovered in the 16th century. Located in the southern hemisphere, this small constellation is bordered by the constellations of Caelum, Canis Major, Lepus, Pictor, and Puppis.

Name and Meaning:

Since Columba was unknown to the ancient Greeks and Romans, no mythlogy is associated with it, but its original name was Columba Noachi, which refers to the Torah’s and Bible’s Dove of Noah that was the first bird to find land after the Deluge.

It could also belong to the story of Argo, where a dove was sent out to lead the Argonauts to safety between the clashing rocks. The legend of the dove is supported by the brightest star in the constellation – Alpha – whose name is Phact, Arabic for “ring dove”.

The constellation seen as “Columba Noachi” in Urania’s Mirror (1825). Credit: US Library of Congress/Wikipedia Commons

History of Observation:

Columba first appeared on the constellation charts of Petrus Plancius – a sixteen century Dutch astronomer and cartographer. In 1589, he created a celestial globe using what little information he could gather from the times explorers to help “fill in” the blank area around the south celestial pole.

Columba was then introduced into a large wall map of the constellations in 1592 and later included in Johann Bayer’s Uranometria sky atlas. In 1920, it was included among the 88 constellations recognized by the IAU, where it has remained to this day.

Notable Objects:

Columba has several major stars associated with it. The brightest is Alpha Columbae (aka. Phact), which is located approximately 270 light years from Earth. Phact is a double star that belongs to the spectral class B7IVe, and is omposed of a Be-type subgiant and a faint companion star. Its name is derived from the Arabic world Al-Fakhita, which means “the dove”.

Beta Columbae (aka. Wezn) is the second brightest star in the constellation, a giant K1-type star located 86 light years from Earth. It’s name is derived from the Arabic word Al-Wazen, which means “the weight”. Third is Delta Columbae (aka. Ghusn al Zaitun), a spectroscopic binary that is located approximately 237 light years away. Its name is derived from the Arabic phrase al-ghasn alzzaytun, which means “olive branch.”

The barred spiral galaxy NGC 1808. Credit: Jim Flood (Amateur Astronomers Inc., Sperry Observatory), Max Mutchler (STScI)

Columba is also home to several Deep Sky Objects. There’s NGC 1808, a barred spiral galaxy that is located approximately 40 million light years from Earth. Similar in many ways to the Milky Way, this galaxy has an unusual nuclear which is shaped like a warped disk and is believed to have a lot of star-forming activity within it.

There’s also NGC 1851 (aka. Caldwell 73), is a globular cluster located approximately 39,500 light years away, and NGC 1792, a starburst spiral galaxy that also goes by the name Bulliens Columbae (or the “bubbling galaxy”). This is due to its appearance, which is characterized by the patchy distribution of dust throughout the galaxy and the way this dust is heated by young stars.

Last, there’s ESO 306-17, a fossil group giant elliptical galaxy that is located at a distance of about 493 million light years from Earth. The galaxy spans about 1 million light years in diameter and is believed to have cannibalized smaller galaxies in its neighbourhood. Hence why it is designated as a fossil group, which refers to the fact that it is believed to be the end-result of a galaxy colliding and merging with a regular galaxy group.

Finding Columba:

Columba consists of 1 bright star and 5 primary stars, with 18 Bayer/Flamsteed designated stellar members. It is bordered by the constellations of Lepus, Caelum, Pictor, Puppis and Canis Major. Columba is easily visible to viewers at latitudes between +45° and -90° and is best seen at culmination during the month of February.

The globular cluster NGC 1851. Credit: NASA, JPL-Caltech, SSC

Get out your telescope and take a look at Alpha Columbae – the A symbol on the map. Here we have a a subgiant star – a star that has just stopped fusing hydrogen to helium – with an an apparent magnitude of approximately 2.6. Located about 268 light years from Earth, Phact is spinning rapidly… at a speed of at least 180 kilometers per second at its equator.

That’s over 90 times faster than our Sun! This rapid rotation causes Phact to flatten at its poles and to spin off a low density envelope about twice its radius. Now, look closely you’ll see that Phact is actually a binary star system. Its faint companion has an apparent magnitude of 12.3 and is 13.5″ distant from the main star.

Now aim binoculars at Beta Columbae – the B symbol on the map. Its proper name is Wazn the “Weight”. If you don’t think there is anything particularly interesting about this 86 light-year distant, spectral class K1IIICN+1, 3.12 magnitude star, then you better think again. This calm looking, core helium fusing giant star might be a little on the small side as giant stars go, but it is about 12 times the size of our own Sun and shines 53 times brighter.

Of course, that’s not all that unusual either. Nor is the fact that Wazn is about 2 billion years old. What is really strange is that Beta Columbae is scooting along through space at a speed of 103 kilometers per second. That’s about six to seven time faster than what’s considered “normal”! Why? It’s a runaway star, just like Mu Columbae.

Turn your binoculars toward the U symbol on the map and have a look. At 1,300 light years from our solar system, Mu is one of the few O-class stars that is visible to the unaided eye. Like Phact, Mu is a relatively fast rotating star that completes a full revolution approximately every 1.5 days.

Colour composite image of the starburst spiral galaxy NGC 1792. Credit: ESO

But Mu is also like Wazn – speeding along at relative velocity of over 200 km/s. Just where did these these two “runaways” come from? Chances are Wazn came from the other side of the Milky Way, while Mu may have originated from a binary star collision in Orion. Catch them while they’re still there!

Now aim your binoculars or telescopes at 7th magnitude globular cluster, NGC 1851 (RA 5 14 6.7 Dec -40 2 48). This Class II beauty was discovered by James Dunlop on May 29, 1826 and cataloged as Dunlop 508. What you’ll find is a very rich, almost impenetrable core surrounded by a nice halo of resolvable stars in a delightful field.

NGC 1851 has two distinct stellar populations with very different initial metal mixtures: a normal alpha-enhanced component, and one characterized by strong anti correlations among the CNONa abundances. Known in the Caldwell Catalog as Object 73, this fine object does well in all aperture sizes – even to Dunlop who almost 200 years ago wrote:

“An exceedingly bright, round, well-defined nebula, about 1.5′ diameter, exceedingly condensed, almost to the very margin. This is the brightest small nebula that I have seen. I tried several magnifying powers on this beautiful globe; a considerable portion round the margin is resolvable, but the compression to the centre is so great that I cannot reasonably expect to separate the stars. I compared this with the 68 Conn. des Temps, and this nebula greatly exceeds the 68 in condensation and brightness.”

Image of ESO 306-17, taken by the Advanced Camera for Surveys aboard the NASA/ESA Hubble Space Telescope. Credit: NASA/ESA/Michael West (ESO)

For a telescope challenge, try NGC 1792 (RA 05 05.2 Dec -37 59). Despite being billed at slightly fainter than magnitude 10, you’ll find the surface brightness of this spiral galaxy a little more in need of larger aperture. Noted as a starburst galaxy, NGC 1792 has a patchy distribution of dust throughout the galactic disc. The galaxy itself is abundant in neutral hydrogen gas and is in the star formation process.

The galaxy is characterized by unusually luminous far-infrared radiation from the young stars heating the dust with their intense activity. This activity could be caused by gravitational interaction with galaxy NGC 1808 (RA 5 7 42.3 Dec -37 30 47) – also a Seyfert galaxy. Easily seen in larger telescopes as an elongated glow, with a bright, round central core. There’s a reason for that…

The barred spiral galaxy NGC 1808 is undergoing an episode of intense star formation near its very center, perhaps triggered by rotation of the bar or by material transported inward along the bar. This new star formation is somehow being organized into clusters of between 10 and 100 light years in diameter, and filaments of dark, obscuring dust are mixed in with the gas and stars.

Thanks to studies done with the XMM-Newton and Chandra observatories, they have directly proved the co-existence of thermal diffuse plasma and non-nuclear unresolved point-like sources associated with the starburst activity, along with a Low Luminosity Active Galactic Nucleus (LLAGN) or an Ultra Luminous X-ray source (ULX). What a show!

Now try your luck with galactic star cluster NGC 1963 (RA 05 32.2 Dec -36 23). While it is not a very rich and populous star cluster, it is an interesting stellar association of perhaps two dozen stars arranged in chains over a wide field with a size of 10.0′. Look for an asterism that appears like the number 3!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Source:

The Circinus Constellation

Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with the compass – the Circinus constellation!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

Over time, the number of recognized constellations has grown as astronomers and explorers became aware of other stars visible from other location around the world. By the 20th century, the IAU adopted a modern catalog of 88 Constellations. One of these is the Circinus constellation, a small, faint constellation located in the southern skies. It is bordered by the constellations Apus, Centaurus, Lupus, Musca, Norma, Triangulum Australe.

Name and Meaning:

Because Circinus was unknown to the ancient Greeks and Romans, it has no mythology associated with it. The three brightest stars form a narrow triangle. The shape is reminiscent of a drawing (or drafting) compass of the sort used to plot sea and sky charts. Nicolas Louis de Lacaille had a fascination with secular science and the thought of naming a constellation after a science tool fascinated him.

Lacaille’s table, showing his representations of the constellations. Credit: gallica.bnf.fr

In this case, Circinus represents a drafting tool used in navigation, mathematics, technical drawing, engineering drawing, in cartography (drawing maps) – and which many elementary school age children use to learn to draw circles and in geometry to bi-sect lines, draw arcs and so forth. In this case, the device should not be confused with Pyxis, a constellation associated with a ship’s compass… despite the similarity in names with the Latin language!

History of Observation:

The small, faint southern constellation Circinus was created by Nicholas de Lacaille during his stay at the Cape of Good Hope in the mid-18th century. Circinus was given its current name in 1763, when Lacaille published an updated sky map with Latin names for the constellations he introduced.

On the map he created, Lacaille portrayed the constellations of Norma, Circinus, and Triangulum Australe as a set of draughtsman’s instruments – as a ruler, compass, and a surveyor’s level, respectively. This constellation has endured and became one of the 88 modern constellation recognized by the IAU in 1920.

Notable Features:

Circinus has no bright stars and consists of only 3 main stars and 9 Bayer/Flamsteed designated stars. However, the constellation does have several Deep Sky Objects associated with it. For instance, there’s the Circinus Galaxy, a spiral galaxy located approximately 13 million light years distant that was discovered in 1975. The galaxy is notable for the gas rings inside it, one of which is a massive star-forming region, and its black hole-powered core.

Composite image of the central regions of the nearby Circinus galaxy, located about 12 million light years away. Credit: NASA/Chandra/HST

Then there’s the X-ray double star known as Circinus X-1, which is located approximately 30,700 light years away and was discovered in 1969. This system is composed of a neutron star orbiting a main sequence star. Circinus is also home to the bright planetary nebula known as NGC 5315, which was created when a star went supernova and cast off its outer layers into space.

Then there’s NGC 5823 (aka. Caldwell 88), an open cluster located on the border between Circinus and Lupus. Located about 3,500 light years away, this cluster is about 800 million years old and spans about 12 light years.

Finding Circinus:

Circinus is visible at latitudes between +10° and -90° and is best seen at culmination during the month of June. Start by taking out your binoculars for a look at Alpha Circini – a great visual double star. Located about 53.5 light years from Earth, this stellar pair isn’t physically related but does make a unique target. The brighter of the two, Alpha, is a F1 Bright Yellow Dwarf that is a slight variable star. This contrasts very nicely with the fainter, red companion.

For the telescope, take a look at Gamma Circini – a faint star a little over five hundred light years from the Solar System. In the sky, it lies in the Milky Way, between bright Alpha Centauri and the Southern Triangle. Gamma Circini is a binary system, containing a blue giant star with a yellow, F-type, companion. Gamma is unique because it possess a stellar magnetic buoyancy!

Location of the Circinus constellation. Credit: IAU

For larger binoculars and telescopes, have a look at galactic star cluster NGC 5823 (RA 15 : 05.7 Dec -55 : 36). This dim cluster will appear to have several brighter members which are actually foreground stars, but does include Mira-type variable Y Circini. While it will be hard to distinguish from the rich, Milky Way star fields, you will notice an elliptical shaped compression of stars with an asterism which resembles and open umbrella.

For large telescopes, check out ESO 97-G13 – the “Circinus Galaxy”. Located only 4 degrees below the Galactic plane, and 13 million light-years away (RA 14h 13m 9.9s Dec 65° 20? 21?), this Seyfert Galaxy is undergoing tumultuous changes, as rings of gas are being ejected from the galactic core. While it can be spotted in a small telescope, science didn’t notice it until 25 years ago!

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

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The Chamaeleon Constellation

Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with that famous lizard that specializes at blending in – the Chamaeleon constellation!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

In time, this list would come to be expanded as astronomers became aware of more asterisms in the night sky. One of these is Chamaeleon, a small constellation located in the southern sky that was first defined in the 16th century. This constellation was appropriately named, given its ability to blend into the background! Today, it is one of the 88 constellations recognized by the IAU.

Name and Meaning:

Since Chamaeleon was unknown to the ancient Greeks and Romans, it has no mythology associated with it, but it’s not hard to understand how it came about its fanciful name. As exploration of the southern hemisphere began, what biological wonders were discovered! Can you imagine how odd a creature that could change its skin color to match its surroundings would be to someone who wasn’t familiar with lizards?

Map of the dark molecular clouds associated with the Chamaeleon constellation. Credit: Roberto Mura

Small wonder that a constellation that blended right in with the background stars could be considered a “chamaeleon” or that it might be pictured sticking its long tongue out to capture its insectile constellation neighbor – Musca the “fly”!

History of Observation:

Chamaeleon was one of twelve constellations created by Pieter Dirkszoon Keyser and Frederick de Houtman between 1595 and 1597. Both were Dutch navigators and early astronomical explorers who made attempts to chart southern hemisphere skies. Their work was added to Johann Bayer’s “Uranometeria” catalog in 1603, where Chamaeleon was first introduced as one of the 12 new southern constellations and its stars given Bayer designations.

To this day, Chamaeleon remain as one of the 88 modern constellations recognized by the IAU and it is bordered by Musca, Carina, Volans, Mensa, Octans and Apus. It contains only 3 main stars, the brightest of which is 4th magnitude Alpha – but it also has 16 Bayer/Flamsteed designated stars within its boundaries.

Notable Features:

The Chamaeleon constellation is home to several notable stars. These include Alpha Chamaeleontis, a spectral type F5III star located approximately 63.5 light years from Earth. Beta Chamaeleontis is a main sequence star that is approximately 270 light years distant. This star is the third brightest in the constellation, after Alpha and Gamma Chamaeleontis.

Artist’s concept of “hot Jupiter”, a Jupiter-sized planet orbiting closely to its star. Credit: NASA/JPL-Caltech

And then there’s HD 63454, a K-type main sequence star located approximately 116.7 light years away. It lies near the south celestial pole and is slightly cooler and less luminous than the Sun. In February of 2005, a hot Jupiter-like planet (HD 63454 b) was discovered orbiting the star.

The “Chamaeleon” also disguises itself with a huge number of dark molecular clouds that are often referred to as the “Chamaeleon Cloud Complex”. Situation about 15 degrees below the galactic plane, it is accepted is one of the closest low mass star forming regions to the Sun with a distance of about 400 to 600 light years.

Within these clouds are pre-main sequence star candidates, and low-mass T Tauri stars. The southern region of the Chamaeleon Cloud is a complex pattern of dark knots connected by elongated, dark, wavy filaments, with a serpentine-like shape. Bright rims with finger-like extensions are apparent, and a web of very faint, extremely thin but very long and straight shining filaments.

These feeble structures, reflecting stellar light, extend over the entire Chamaeleon complex and are considered very young – not yet capable of the type of collapse needed to introduce major star formation. Thanks to Gemini Near Infrared Spectrograph (GNIRS) on Gemini South Telescope, a very faint infrared object confirmed – a very low-mass, newborn brown dwarf star and the lowest mass brown dwarf star found to date in the Chamaeleon I cloud complex.

A newly formed star lights up the surrounding cosmic clouds in this image from ESO’s La Silla Observatory in Chile. Credit: ESO

Chamaeleon is also home to the Eta Chamaeleontis Cluster (aka. Mamajek 1). This open star cluster, which is centered on the star Eta Chamaeleontis, is approximately 316 light years distant and believed to be around eight million years old. The cluster was discovered in 1999 and consists of 12 or so relatively young stars. It was also the first open cluster discovered because of its X-ray emissions its member stars emit.

Finding Chamaeleon:

Chamaeleon is visible at latitudes between +0° and -90° and is best seen at culmination during the month of April. Now take out your telescope and aim it towards Eta for a look at newly discovered galactic star cluster – the Eta Chamaeleontis cluster – Mamajek 1. In 1999, a cluster of young, X-ray-emitting stars was found in the vicinity of eta Chamaeleontis from a deep ROSAT high-resolution imager observation.

They are believed to be pre-main-sequence weak-lined T Tauri stars, with an age of up to 12 million years old. The cluster itself is far from any significant molecular cloud and thus it has mysterious origins – not sharing proper motions with other young stars in the Chamaeleon region. There’s every possibility it could be a moving star cluster that’s a part of the Scorpius/Centaurus OB star association!

For binoculars, take a look at fourth magnitude Alpha Chamaeleontis. It is a rare class F white giant star that is about 63.5 light years from Earth. It is estimated to be about 1.5 billion years old. Its spectrum shows it to be a older giant with a dead helium core, yet its luminosity and temperature show it to be a younger dwarf.

The location of the Chamaeleon Constellation. Credit: IAU /Sky&Telescope magazine

Now point your binoculars or telescope towards Delta Chamaeleontis. While these two stars aren’t physically connect to one another, the visual double star is exceptionally pleasing with one orange component and one blue.

Last, but not least, take a look at Gamma Chamaeleontis. Although the south celestial pole currently lacks a bright star like Polaris to mark its position, the precession of the equinoxes will change that. One day – in the next 7500 years – the south celestial pole will pass close to the stars Gamma Chamaeleontis. But don’t wait up…

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Sources:

Did A Comet Impact Push Humans Into Technological Overdrive?

About 14,500 years ago, Earth began transitioning from its cold, glacial self to a warmer interglacial state. However, partway through this period, temperatures suddenly returned to near-glacial conditions. This abrupt change (known as the Younger Dryas period) is believed by some to be the reason why hunter-gatherers started forming sedentary communities, farming, and laying the groundwork for civilization as we know it – aka. the Neolithic Revolution.

For over a decade, there have been scientists who have argued that this period was the result of a comet hitting Earth. Known as the Younger Dryas Impact Hypothesis (aka. the Clovis Comet Hypothesis), the theory is largely based on ice core samples from Greenland that show a sudden global temperature change. But according to a new study by a research team from the University of Edinburgh, archaeological evidence may also prove this hypothesis correct.

The Younger Dryas period takes its name from a species of flower known as Dryas octopetala. This plant is known to grow in cold conditions, and became common in Europe during the period. Because of the way it began abruptly – roughly 12,500 years ago – and then ended just as abruptly 1200 years later, many scientists are convinced it was caused by an external event.

Göbekli Tepe, structures A-D of the site, located in southern Turkey. Credit: Wikipedia Commons/Teomancimit

For the sake of their study – which was recently published in the journal Mediterranean Archaeology and Archaeometry under the title “Decoding Göbekli Tepe With Archaeoastronomy: What Does the Fox Say?“- the team found an astronomical link to the stone pillars at Göbekli Tepe. Located in southern Turkey, this archaeological find is the oldest known temple site in the world (dated to ca. 10,950 BCE).

This site, it should be noted, is contemporary with the Greenland ice core samples, which are dated to around 10,890 BCE. Of the sites many features, none are more famous than the many standing pillars that dot the excavated grounds. This is because of the extensive pictograms and animal reliefs that decorate these pillars, which include various representations of mammal and avian species- particularly vultures.

Pillar 43, which is also known as the “vulture stone”, was of particular interest to archeologists, as it is suspected that its representations (associated with death) could have been intended to commemorate a devastating event. The other images, they ventured, were meant to depict the constellations, and that their placement relative to each other accorded to the positions of the then-known asterisms in the night sky.

This theory was based on images they took of the site, which they then examined using the planetarium program stellarium 0.15. In the end, they found that the images bore a resemblance to constellations that would have been visible in 10,950 BCE. As such, they concluded that the temple site may have been an observatory, and that the images were a catalog of celestial events – which include the Taurid meteor stream.

Wall pillars with three animal symbols in series. Part a) is pillar 2 from Enclosure A, while part b) is pillar 38, Enclosure D. Credit: Travel The Unknown

As they state in their study:

“We begin by noting the carving of a scorpion on pillar 43, a well -known zodiacal symbol for Scorpius. Based on this observation, we investigate to what extent other symbols on pillar 43 can be interpreted as zodiacal symbols or other familiar astronomical symbols… We suggest the vulture/eagle on pillar 43 can be interpreted as the ‘teapot’ asterism of our present-day notion of Sagittarius; the angle between the eagle/vulture’s head and wings, in particular, agrees well with the ‘handle’,‘lid’ and ‘spout’ of the teapot asterism. We also suggest the ‘bent-bird’ with downward wriggling snake or fish can be interpreted as the ‘13th sign of the zodiac’, i.e. of our present-day notion of Ophiuchus. Although its relative position is not very accurate, we suggest the artist(s) of pillar 43 were constrained by the shape of the pillar. These symbols are a reasonably good match with their corresponding asterisms, and they all appear to be in approximately the correct relative locations.

Similarly, they suggest that a carved circle at the center of pillar 43 could be interpreted as the Sun. They call this image the “date stamp” because it can be seen as communicating a specific date by indicating which part of the zodiac the Sun was in at the time of carving. By comparing the age of the site (based on carbon dating) to the apparent position of the Sun, they found that it was consistent with the Summer solstice of 10,950 BCE.

Of course, the team fully acknowledges that an astronomical interpretation is by no means the only possibility. In addition to the possibility of them being mythological references, they could also be representations of hunting or migration patterns. It’s also entirely possible they were not meant to convey any specific meaning, and were merely a description of the local environment, which would have been rich in flora and fauna at the time.

Pillar 43, Enclosure D, also known as the Vulture Stone of Göbekli Tepe. Credit: Martin B. Sweatman and Dimitrios Tsikritsis

In addition, the way vultures are commonly featured could be an indication that the site was a burial ground. This is consistent with iconography found at the archaeological sites of Çatalhöyük (in central, southern Turkey) and Jericho (in the West Bank). During the time period in question, Neolithic peoples were known to conduct sky burials, where the bodies of the deceased were left out in the open for carrion birds to pick over.

In such practices, the head was sometimes removed from the deceased and kept (for the sake of ancestor worship). This is consistent with one of the characters on Pillar 43, which appears to be a headless human. However, as the team go on to explain, they are confident that the connection between the site’s images and the Taurid meteor stream is a plausible one.

“[O]ur basic statistical analysis indicates our astronomical interpretation is very likely to be correct,” they write. “We are therefore content to limit ourselves to this hypothesis, and logically we are not required to pursue others.” And of course, they acknowledge that further research will be necessary before any conclusions can be made.

Despite the availability of other (and perhaps more plausible) explanations, one has to admit that the astronomical theory is appealing. Civilization as we know it being a response to a meteor impact, and ancient people cataloging it in their stone carvings. It’s got a real Deep Impact meets 2001: A Space Odyssey feel to it!

Further Reading: MAA Journal