Welcome to another edition of Constellation Friday! Today, in honor of the late and great Tammy Plotner, we take a look at the “Swan” – the Cygnus 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 the constellations identified by Ptolemy was Cygnus, otherwise known as “the Swan”. The constellation is easy to find in the sky because it features a well-known asterism known as the Northern Cross. Cygnus was first catalogued the by Greek astronomer Ptolemy in the 2nd century CE and is today one of the 88 recognized by the IAU. It is bordered by the constellations of Cepheus, Draco, Lyra, Vulpecula, Pegasus and Lacerta.
Name and Meaning:
Because the pattern of stars so easily resembles a bird in flight, Cygnus the “Swan” has a long and rich mythological history. To the ancient Greeks, it was at one time Zeus disguising himself to win over Leda, and eventually father Gemini, Helen of Troy, and Clytemnestra. Or perhaps it is poor Orpheus, musician and muse of the gods, who when he died was transformed into a swan and placed in the stars next to his beloved lyre.
It could be king Cycnus, a relative of Phaethon, son of Apollo, who crashed dear old dad’s fiery sky chariot and died. Cygcus was believed to have driven up and down the starry river so many times looking for Phaethon’s remains that he was finally transformed into stars. No matter what legend you choose, Cygnus is a fascinating place… and filled with even more fascinating areas to visit!
History of Observation:
Because of its importance in ancient Greek mythology and astrology, the sprawling constellation of Cygnus was one of Ptolemy’s original 48 constellations. To Hindu astronomers, the Cygnus constellation is also associated with the “Brahma Muhurta” (“Moment of the Universe”). This period, which lasts from 4:24 AM to 5:12 AM, is considered to be the best time to start the day.
Cygnus is also highly significant to the folklore and mythology of many people in Polynesia, who also viewed it as a separate constellation. These include the people of Tonga, the Tuamatos people, the Maori (New Zealand) and the people of the Society Islands. Today, Cygnus is one of the official 88 modern constellations recognized by the IAU.
Flying across the sky in a grand position against the backdrop of the Milky Way, Cygnus consists of 6 bright stars which form an asterism of a cross comprised of 9 main stars and there are 84 Bayer/Flamsteed designated stars within its confines. It’s most prominent star, Deneb (Alpha Cygni), takes it name from the Arabic word dhaneb, which is derived from the Arabic phrase Dhanab ad-Dajajah, which means “the tail of the hen”.
Deneb is a blue-white supergiant belonging to the spectral class A2 Ia, and is located approximately 1,400 light years from Earth. In addition to being the brightest star in Cygnus, it is one of the most luminous stars known. Being almost 60,000 times more luminous than our Sun and about 20 Solar masses, it is also one of the largest white stars known.
Deneb serves as a prototype for a class of variable stars known as the Alpha Cygni variables, whose brightness and spectral type fluctuate slightly as a result of non-radial fluctuations of the star’s surface. Deneb has stopped fusing hydrogen in its core and is expected to explode as a supernova within the next few million years. Together with the stars of Altair and Vega, Deneb forms the Summer Triangle, a prominent asterism in the summer sky.
Next up is Gamma Cygni (aka. Sadr), whose name comes from the Arabic word for “the chest”. It is also sometimes known by its Latin name, Pectus Gallinae, which means “the hen’s chest.” This star belongs to the spectral class F8 lad, making it a blue-white supergiant, and is located approximately 1,800 light years from Earth.
It can easily seen in the night sky at the intersection of the Northern Cross thanks to its apparent magnitude of 2.23, which makes it one of the brightest stars that can be seen in the night sky. It is also believed to be only about 12 million years old and consumes its nuclear fuel more rapidly because of its mass (12 Solar masses).
Then there’s Epsilon Cygni (ak. Glenah), an orange giant of the spectral class K0 III that is 72.7 light years distant. It’s traditional name comes from the Arabic word janah, which means “the wing” (this name is shared with Gamma Corvi, a star in the Corvus constellation). It is 62 times more luminous than the Sun and measures 11 Solar radii.
Delta Cygni (Rukh), is a triple star system in Cygnus, which is located about 165 light years away. The system consists of two stars lying close together and a third star located a little further from the main pair. The brightest component is a blue-white fast-rotating giant belonging to the spectral class B9 III. The star’s closer companion is a yellow-white star belonging to the spectral class F1 V, while the third component is an orange giant.
Last, there’s Beta Cygni (aka. Albireo) which is only the fifth brightest star in the constellation Cygnus, despite its designation. This binary star system, which appears as a single star to the naked eye, is approximately 380 light-years distant. The traditional name is the result of multiple translations and misunderstandings of the original Arabic name, minqar al-dajaja (“the hen’s beak”). It is one of the stars that form the Northern Cross.
The binary system consists of a yellow star which is itself a close binary star that cannot be resolved as two separate objects. Its second star is a fainter blue fast-rotating companion star with an apparent magnitude of 5.82 that is located 35 arc seconds apart from its primary.
Cygnus is also home to a number of Deep Sky Objects. These include Messier 29 (NGC 6913), an open star cluster that is about 10 million years old and located about 4,000 light years from Earth. It can be spotted with binoculars a short distance away from Gamma Cygni – 1.7 degrees to the south and a little east.
Next up is Messier 39 (NGC 7092), another open star cluster that is located about 800 light-years away and is between 200 and 300 million years old. All the stars observed in this cluster are in their main sequence phase and the brightest ones will soon evolve to the red giant stage. The cluster can be found two and a half degrees west and a degree south of the star Pi-2 Cygni.
There is also the Fireworks Galaxy (NGC 6946), an intermediate spiral galaxy that is approximately 22.5 million light-years distant. The galaxy is located near the border of the constellation Cepheus and lies close to the galactic plane, where causes it to become obscured by the interstellar matter of the Milky Way.
Then there’s the famous X-ray source known as Cygnus X-1, which is one of the strongest that can be seen from Earth. Cygnus X-1 is notable for being the first X-ray source to be identified as a black hole candidate, with a mass 8.7 times that of the Sun. It orbits a blue supergiant variable star some 6,100 light-years away, which is one of two stars form a binary system.
Over time, an accretion disk of material brought from the star by a stellar wind has formed around Cygnus X-1, which is the source of its X-ray emissions.
Cygnus is visible to all observers at latitudes between +90° and -40° and is best seen at culmination during the month of September. For a period of 15 days around the peak date of August 20, watch for the Kappa Cygnid meteor shower. This annual meteor shower has a radiant near the bright star Deneb and an average fall rate of about 12 meteors per hour. It is noted to have many bright fire balls called “bolides” and the best time to watch is when the constellation is directly overhead.
Because Cygus is so rich in things to visit, we shall only touch very briefly on just a few. Let’s begin with our unaided eye as we take a look at the brightest star of the constellation, Alpha Cygni – Deneb. Here we have not only an extremely luminous blue super giant star – but a pulsing variable star, too. Its changes are minor – only about 1/10 of a stellar magnitude, but Deneb is its own prototype.
Its stellar oscillations are very complex, consisting of multiple pulsation frequencies as well as a fundamental one. This means changes in brightness occur between 5 and 10 days apart, but that’s a good thing. If the changes weren’t small, Deneb would blow itself to bits!
If you are looking at Cygnus for an area well away from city lights on a night when there is no Moon, look just northwest of Deneb for the North America Nebula (NGC 7000). This is an excellent emission nebula that covers as much area of the sky as 10 full Moons! At 3 full degrees, you’ll be looking for a vague, misty patch of silver-ness that about as broad as your thumb held at arm’s length.
While telescopes and binoculars are grand, remember this particular region is so large that you can easily over magnify it and often your unaided eye is all you need to catch this elusive interstellar cloud of ionized hydrogen (H II region). Now, get out your binoculars and let’s dance!
Messier 29 is very easy and bright and you can find it about a fingerwidth south and a little east of Gamma Cygni – the “8” shape on our map. This open cluster of stars has just a handful of bright members and will look like a small rendition of the “Big Dipper”. M29 is about 7,200 light years away from Earth, so the fact we can see it at all in binoculars is pretty impressive! Now, try Messier 39.
You’ll find this one about a fingerwidth west and southwest of Pi2, which looks like TT2 on our map. This galactic star cluster is far brighter and richer than the last. It will show as a triangle shape with bright stars in each corner and a couple of dozen fainter stars captured within the center. M39 is only about 800 light years away from our solar system, but it could be as much as 300 million years old!
Don’t put your binoculars away just yet. You’ve got to visit Omega 2 before you stop! Its name is Ruchbah and it’s a double star about 500 light years from Earth, consisting of a magnitude 5.44 star of spectral class M2 and a 6.6 magnitude star of spectral class A0. The stars are well separated at 256″ apart and can be seen in binoculars and totally glorious in a telescope. Because of the color contrast (red main star and blue companion), Ruchba is a beautiful object for amateur astronomers.
Now try Beta Cygni – Albireo. It is also known as one of the most attractive and colorful double stars in the sky. Beautiful Beta 1 is an orange giant K star and Beta 2 is a main-sequence B star of a soft, blue hue. If you can’t separate them in your binoculars, use a telescope! This seasonal favorite is one that’s not to be missed! Now, let’s try a couple objects for the telescope.
One of the true prizes of the Cygnus region for any telescope is the Holy Veil (NGC 6960, 6962, 6979, 6992, and 6995). You’ll find it just south of Epsilon Cygni and the easiest segment to find is 6960, which runs through the star 52 Cygni. This is an ancient supernova remnant covering approximately 3 degrees of the sky and an experience you won’t soon forget if you are viewing from a dark sky site.
The source supernova exploded some 5,000 to 8,000 years ago and it is simply amazing to think that anything remains to be seen. It was discovered on 1784 September 5 by William Herschel. He described the western end of the nebula as “Extended; passes thro’ 52 Cygni… near 2 degree in length.” and described the eastern end as “Branching nebulosity… The following part divides into several streams uniting again towards the south.”
Even though it is any where from from 1,400 to 2,600 light-years light years away, you’ll find long and wondrous tongues of material to capture your interest and delight your eye and you follow them to their ends!
More challenging is the Crescent Nebula (NGC 6888 or Caldwell 27) located at RA 20h 12m 7s Dec +38 21.3′. This is an emission nebula fueled by a Wolf-Rayet star located about 5000 light years away. It is formed by the fast stellar wind careening off illuminating the slower moving wind ejected by the star when it went into the red giant star stage. What’s left is a collision… a shell and two shock waves… one moving outward and one moving inward. A what a grand one it is!
For galaxy fans, you have got to point your telescope towards NGC 6946, the “Fireworks Galaxy” (RA 20h 34m 52.3s Dec +60 09 14). Who cares if this barred spiral galaxy 10 million light years away? This is one supernovae active baby! At one time, it was widely believed that NGC 6946 was a member of our Local Group; mainly because it could be easily resolved into stars.
There was a reddening observed in it, believed to be indicative of distance – but now know to be caused by interstellar dust. But it isn’t the shrouding dust cloud that makes NGC 6946 so interesting, it’s the fact that so many supernova and star-forming events have sparkled in its arms in the last few years that has science puzzled! So many, in fact, that they’ve been recorded every year or two for the last 60 years…
Now, for the really cool part – understanding barred structure. Thanks to the Hubble Space Telescope and a study of more than 2,000 spiral galaxies – the Cosmic Evolution Survey (COSMOS) – astronomers understand that barred spiral structure just didn’t occur very often some 7 billion years ago in the local universe. Bar formation in spiral galaxies evolved over time.
A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts. This makes NGC 6946 very rare, indeed… Since its barred structure was noted back in Herschel’s time and its age of 10 billion years puts it beyond what is considered a “modern” galaxy.
It that all there is? Not hardly. Try NGC 6883, an open cluster located about 3 degrees east/northeast of Eta Cygni. It’s a nice, tight cluster that involves a well-resolved double star and a bonus open cluster – Biurakan 2 – as well. Or how about NGC 6826 located about 1.3 degrees east/northeast of Theta. This one is totally cool… the “Blinking Planetary”!
This planetary nebula is fairly bright and so is the central star… but don’t stare at it, or it will disappear! Look at it averted and the central star will appear again. Neat trick, huh? Now try NGC 6819 about 8 degrees west of Gamma. Here you’ll find a very rich, bright open cluster of about 100 stars that’s sure to please. It’s also known as Best 42!
There’s many more objects in Cygnus than just what’s listed here, so grab yourself a good star chart and fly with the “Swan”!
Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with the sea monster – the Cetus 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 constellations is Cetus, which was named in honor of the sea monster from Greek mythology. Cetus is the fourth largest constellation in the sky, the majority of which resides just below the ecliptic plane. Here, it is bordered by many “watery” constellations – including Aquarius, Pices, Eridanus, Piscis Austrinus, Capricornus – as well as Aries, Sculptor, Fornax and Taurus. Today, it is one of the 88 modern constellations recognized by the IAU.
Name and Meaning:
In mythology, Cetus ties in with the legendary Cepheus,Cassiopeia, Andromeda, Perseus tale – for Cetus is the monster to which poor Andromeda was to be sacrificed. (This whole tale is quite wonderful when studied, for we can also tie in Pegasus as Perseus’ horse, Algol and the whom he slew to get to Andromeda and much, much more!)
As for poor, ugly Cetus. He also represents the gates to the underworld thanks to his position just under the ecliptic plane. Arab legend has it that Cetus carries two pearl necklaces – one broken and the other intact – which oddly enough, you can see among its faint stars in the circular patterns when nights are dark. No matter what the legends are, Cetus is an rather dim, but interesting constellation!
History of Observation:
Cetus was one of many Mesopotamian constellations that passed down to the Greeks. Originally, Cetus may have been associated with a whale, and is often referred to as the Whale. However, its most common representation is that of the sea monster that was slain by Perseus.
In the 17th century, Cetus was depicted variously as a “dragon fish” (by Johann Bayer), and as a whale-like creature by famed 17th-century cartographers Willem Blaeu and Andreas Cellarius. However, Cetus has also been variously depicted with animal heads attached to an aquatic animal body.
The constellation is also represented in many non-Western astrological systems.In Chinese astronomy, the stars of Cetus are found among the Black Tortoise of the North (B?i F?ng Xuán W?) and the White Tiger of the West (X? F?ng Bái H?).
Cetus sprawls across 1231 square degrees of sky and contains 15 main stars, highlighted by 3 bright stars and 88 Bayer/Flamsteed designations. It’s brightest star is Beta Ceti, otherwise known as Deneb Kaitos (Diphda), a type K0III orange giant which is located approximately 96.3 light years away. This star has left its main sequence and is on its way to becoming a red giant.
The name Deneb Kaitos is derived from the Arabic “Al Dhanab al Kaitos al Janubiyy”, which translates as “the southern tail of Cetus”. The name Diphda comes “ad-dafda at-tani“, which is Arabic for “the second frog” – the star Fomalhaut in neighboring Piscis Austrinus is usually referred to as the first frog.)
Then there’s Alpha Ceti, a very old red giant star located approximately 249 light years from Earth. It’s traditional name (Menkar), is derived from the Arabic word for “nostril”. Then comes Omicron Ceti, also known as Mira, binary star consisting located approximately 420 light years away. This binary system consists of an oscillating variable red giant (Mira A).
After being recorded for the first time by David Fabricius (on August 3, 1596), Mira has since gone on to become the prototype for the Mira class of variables (of which there are six or seven thousand known examples). These stars are red giants whose surfaces oscillate in such a way as to cause variations in brightness over periods ranging from 80 to more than 1,000 days.
Cetus is also home to many Deep Sky Objects. A notable examples is the barred spiral galaxy known as Messier 77, which is located approximately 47 million light years away and is 170,000 light years in diameter, making it one of the largest galaxies listed in Messier’s catalogue. It has an Active Galactic Nucleus (AGN) which is obscured from view by intergalactic dust, but remains an active radio source.
Then there’s NGC 1055, a spiral galaxy that lies just 0.5 north by northeast of Messier 77. It is located approximately 52 million light years away and is seen edge-on from Earth. Next to Messier 77, NGC 1055 is a largest member of a galaxy group – measuring 115,800 light years in diameter – that also includes NGC 1073 and several smaller irregular galaxies. It has a diameter of about 115,800 light years. The galaxy is a known radio source.
Cetus is the fourth largest constellation in the sky, is visible at latitudes between +70° and -90° and is best seen at culmination during the month of November. Of all the stars in Cetus, the very first you must look for in binoculars is Mira. Omicron Ceti was the very first variable star discovered and was perhaps known as far back as ancient China, Babylon or Greece. The variability was first recorded by the astronomer David Fabricius while observing Mercury.
Now aim your binoculars at Alpha Ceti. It’s name is Menkar and we do know something about it. Menkar is an old and dying star, long past the hydrogen and perhaps even past the helium stage of its stellar evolution. Right now it’s a red giant star but as it begins to burn its carbon core it will likely become highly unstable before finally shedding its outer layers and forming a planetary nebula, leaving a relatively large white dwarf remnant.
Hop down to Beta Ceti – Diphda. Oddly enough, Diphda is actually the brightest star in Cetus, despite its beta designation. It is a giant star with a stellar corona that’s brightening with age – exerting about 2000 times more x-ray power than our Sun! For some reason, it has gone into an advanced stage if stellar evolution called core helium burning – where it is converting helium directly to carbon.
Are you ready to get out your telescope now? Then aim at Diphda and drop south a couple of degrees for NGC 247. This is a very definite spiral galaxy with an intense “stellar” nucleus! Sitting right up in the eyepiece as a delightful oval, the NGC 247 is has a very proper galaxy structure with a defined core area and a concentration that slowly disperses toward its boundaries with one well-defined dark dust lane helping to enhance a spiral arm. Most entertaining! Continuing “down” we move on to the NGC 253. Talk about bright!
Very few galactic studies come in this magnitude (small telescopes will pick it up very well, but it requires large aperture to study structure.) Very elongated and hazy, it reminds me sharply of the “Andromeda Galaxy”. The center is very concentrated and the spiral arms wrap their way around it beautifully! Dust lanes and bright hints of concentration are most evident. and its most endearing feature is that it seems to be set within a mini “Trapezium” of stars. A very worthy study…
Now, let’s hop off to Delta Ceti, shall we? I want to rock your world – because spiral galaxy M77 rocked mine! Once again, easily achieved in the small telescope, Messier 77 comes “alive” with aperture. This one has an incredible nucleus and very pronounced spiral arms – three big, fat ones! Underscored by dark dust lanes, the arms swirl away from the center in a galactic display that takes your breath away!
The “mottling” inside the structure is not just a hint in this ovalish galaxy. I guarantee you won’t find this one “ho hum”… how could you when you know you’re looking at something that’s 47.0 million light-years away! Messier 77 is an active galaxy with an Active Galactic Nucleus (AGN) and one of the brightest Seyfert galaxies known.
Now, return to Delta and the “fall line” runs west to east on the north side. First up is galaxy NGC 1073, a very pretty little spiral galaxy with a very “stretched” appearing nucleus that seems to be “ringed” by its arms! Continuing along the same trajectory, we find the NGC 1055. Oh, yes… Edge-on, lenticular galaxy! This soft streak of light is accompanied by a trio of stars. The galaxy itself is cut through by a dark dust lane, but what appears so unusual is the core is to one side!
Now we’ve made it to back to the incredible M77, but let’s keep on the path and pick up the NGC 1087 – a nice, even-looking spiral galaxy with a bright nucleus and one curved arm. Ready to head for the beautiful variable Mira again? Then let her be the guide star, because halfway between there and Delta is the NGC 936 – a soft spiral galaxy with a “saturn” shaped nucleus. Nice starhoppin’!
Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with the “keel of the ship”, the Carina 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 the most famous of these constellations is Cassiopeia, which is easily recognized by its W-shape in the sky. As one of the 48 constellation included in the Almagest, it is now one of the 88 modern constellations recognized by the IAU. Located in the norther sky opposite of the Big Dipper (Ursa Major), it is bordered by Camelopardalis, Cepheus, Lacerta, Andromeda and Perseus.
Name and Meaning:
In mythology, Cassiopeia the wife of King Cepheus and the queen of the mythological Phoenician realm of Ethiopia. Her name in Greek means “she whose words excel”, and she was renowned for her beauty but also her arrogance. This led to her downfall, as she boasted that both she and her daughter Andromeda were more beautiful than all the Nereids – the nymph-daughters of the sea god Nereus.
This led the Nerieds to unleash the wrath of Poseidon upon the kingdom of Ethiopia.Accounts differ as to whether Poseidon decided to flood the whole country or direct the sea monster Cetus to destroy it. In either case, trying to save their kingdom, Cepheus and Cassiopeia consulted a wise oracle, who told them that the only way to appease the sea gods was to sacrifice their daughter.
Accordingly, Andromeda was chained to a rock at the sea’s edge and left there to helplessly await her fate at the hands of Cetus. But the hero Perseus arrived in time, saved Andromeda, and ultimately became her husband. Since Poseidon thought that Cassiopeia should not escape punishment, he placed her in the heavens in such a position that, as she circles the celestial pole, she is upside-down for half the time.
History of Observation:
Cassiopeia was one of the traditional constellations included by Ptolemy in his 2nd century CE tract, the Almagest. It also figures prominently in the astronomical and astrological traditions of the Polynesian, Indian, Chinese and Arab cultures. In Chinese astronomy, the stars forming the constellation Cassiopeia are found among the areas of the Purple Forbidden enclosure, the Black Tortoise of the North, and the White Tiger of the West.
Chinese astronomers also identified various figures in its major stars. While Kappa, Eta, and Mu Cassopeiae formed a constellation called the Bridge of the Kings, when combined with Alpha and Beta Cassiopeiae – they formed the great chariot Wang-Liang. In Indian astronomy, Cassiopeia was associated with the mythological figure Sharmishtha – the daughter of the great Devil (Daitya) King Vrishparva and a friend to Devavani (Andromeda).
Arab astronomers also associated Cassiopeia’s stars with various figures from their mythology. For instance, the stars of Alpha, Beta, Gamma, Delta, Epsilon and Eta Cassiopeiae were often depicted as the “Tinted Hand” in Arab atlases – a woman’s hand dyed red with henna, or the bloodied hand of Muhammad’s daughter Fatima. The arm was made up of stars from the neighboring Perseus constellation.
Another Arab constellation that incorporated the stars of Cassiopeia was the Camel. Its head was composed of Lambda, Kappa, Iota, and Phi Andromedae; its hump was Beta Cassiopeiae; its body was the rest of Cassiopeia, and the legs were composed of stars in Perseus and Andromeda.
In November of 1572, astronomers were stunned by the appearance of a new star in the constellation – which was later named Tycho’s Supernova (SN 1572), after astronomer Tycho Brahe who recorded its discovery. At the time of its discovery, SN1572 was a Type Ia supernova that actually rivaled Venus in brightness. The supernova remained visible to the naked eye into 1574, gradually fading until it disappeared from view.
The “new star” helped to shatter stale, ancient models of the heavens by demonstrating that the heavens were not “unchanging”. It helped speed the the revolution that was already underway in astronomy and also led to the production of better astrometric star catalogues (and thus the need for more precise astronomical observing instruments).
To be fair, Tycho was not even close to being the first to observe the 1572 supernova, as his contemporaries Wolfgang Schuler, Thomas Digges, John Dee and Francesco Maurolico produced their own accounts of its appearance. But he was apparently the most accurate observer of the object and did extensive work in both observing the new star and in analyzing the observations of many other astronomers.
This zig-zag shaped circumpolar asterism consists of 5 primary stars (2 of which are the most luminous in the Milky Way Galaxy) and 53 Bayer/Flamsteed designated stars. It’s brightest star – Beta Cassiopeiae, otherwise known by its traditional name Caph – is a yellow-white F-type giant with a mean apparent magnitude of +2.28. It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +2.25 to +2.31 with a period of 2.5 hours.
Now move along the line to the next bright star – Alpha. Its name is Schedar and its an orange giant (spectral type K0 IIIa), a type of star cooler but much brighter than our Sun. In visible light only, it is well over 500 times brighter than the Sun. According to the Hipparcos astrometrical satellite, distance to the star is about 230 light years (or 70 parsecs).
Continue up the line for Eta, marked by the N shape and take a look in a telescope. Eta Cassiopeiae’s name is Achird and its a multiple is a star system 19.4 light years away from Earth. The primary star in the Eta Cassiopeiae system is a yellow dwarf (main sequence star) of spectral type G0V, putting it in the same spectral class as our Sun, which is of spectral type G2V. It therefore resembles what our Sun might look like if we were to observe it from Eta Cassiopeiae.
The star is of apparent magnitude 3.45. The star has a cooler and dimmer (magnitude 7.51) orange dwarf companion of spectral type K7V. Based on an estimated semi major axis of 12″ and a parallax of 0.168 mas, the two stars are separated by an average distance of 71 AU. However, the large orbital eccentricity of 0.497 means that their periapsis, or closest approach, is as small as 36 AU.
The next star in line towards the pole is Gamma, marked by the Y shape. Gamma Cassiopeiae doesn’t have a proper name, but American astronaut Gus Grissom nicknamed it “Navi” since it was an easily identifiable navigational reference point during space missions. The apparent magnitude of this star was +2.2 in 1937, +3.4 in 1940, +2.9 in 1949, +2.7 in 1965 and now it is +2.15. This is a rapidly spinning star that bulges outward along the equator. When combined with the high luminosity, the result is mass loss that forms a disk around the star.
Gamma Cassiopeiae is a spectroscopic binary with an orbital period of about 204 days and an eccentricity alternately reported as 0.26 and “near zero.” The mass of the companion is believed to be comparable to our Sun (Harmanec et al. 2000, Miroschnichenko et al. 2002). Gamma Cas is also the prototype of a small group of stellar sources of X-ray radiation that is about 10 times higher that emitted from other B or Be stars, which shows very short term and long-term cycles.
Now move over to Delta Cassiopeiae, the figure 8. It’s traditional name is Ruchbah, the “knee”. Delta Cassiopeiae is an eclipsing binary with a period of 759 days. Its apparent magnitude varies between +2.68 mag and +2.74 with a period of 759 days. It is of spectral class A3, and is approximately 99 light years from Earth.
Last in line on the end is Epsilon, marked with the backward 3. Epsilon Cassiopeiae’s tradition name is Segin. It is approximately 441 light years from Earth. It has an apparent magnitude of +3.38 and is a single, blue-white B-type giant with a luminosity 720 times that of the Sun.
Cassiopeia constellation is located in the first quadrant of the northern hemisphere (NQ1) and is visible at latitudes between +90° and -20°. It is the 25th largest constellation in the night sky and is best seen during the month of November. Due to its distinctive shape and proximity to the Big Dipper, it is very easy to find. And the constellation has plenty of stars and Deep Sky Objects that can be spotted using a telescope or binoculars.
First, let’s begin by observing Messier 52. This one’s easiest found first in binoculars by starting at Beta, hopping to Alpha as one step and continuing the same distance and trajectory as the next step. M52 (NGC 7654) is a fine open cluster located in a rich Milky Way field. The brightest main sequence star of this cluster is of mag 11.0 and spectral type B7.
Two yellow giants are brighter: The brightest is of spectral type F9 and mag 7.77, the other of type G8 and mag 8.22. Amateurs can see M52 as a nebulous patch in good binoculars or finder scopes. In 4-inch telescopes, it appears as a fine, rich compressed cluster of faint stars, often described as of fan or “V” shape; the bright yellow star is to the SW edge. John Mallas noted “a needle-shaped inner region inside a half-circle.” M52 is one of the original discoveries of Charles Messier, who cataloged it on September 7, 1774 when the comet of that year came close to it.
For larger telescopes, situated about 35′ southwest of M52 is the Bubble Nebula NGC 7635, a diffuse nebula which appears as a large, faint and diffuse oval, about 3.5×3′ around the 7th-mag star HD 220057 of spectral type B2 IV. It is difficult to see because of its low surface brightness. Just immediately south of M52 is the little conspicuous open cluster Czernik 43 (Cz 43).
Now let’s find Messier 103 by returning to Delta Cassiopeiae. In binoculars, M103 is easy to find and identify, and well visible as a nebulous fan-shaped patch. Mallas states that a 10×40 finder resolves the cluster into stars; however, this is so only under very good viewing conditions. The object is not so easy to identify in telescopes because it is quite loose and poor, and may be confused with star groups or clusters in the vicinity.
But telescopes show many fainter member stars. M103 is one of the more remote open clusters in Messier’s catalog, at about 8,000 light years. While you are there, enjoy the other small open clusters that are equally outstanding in a telescope, such as NGC 659, NGC 663 and NGC 654. But, for a real star party treat, take the time to go back south and look up galactic star cluster NGC 457.
It contains nearly one hundred stars and lies over 9,000 light years away from the Sun. The cluster is sometimes referred by amateur astronomers as the Owl Cluster, or the ET Cluster, due to its resemblance to the movie character. Those looking for a more spectacular treat should check out NGC 7789 – a rich galactic star cluster that was discovered by Caroline Herschel in 1783. Her brother William Herschel included it in his catalog as H VI.30.
This cluster is also known as “The White Rose” Cluster or “Caroline’s Rose” Cluster because when seen visually, the loops of stars and dark lanes look like the swirling pattern of rose petals as seen from above. At 1.6 billion years old, this cluster of stars is beginning to show its age. All the stars in the cluster were likely born at the same time but the brighter and more massive ones have more rapidly exhausted the hydrogen fuel in their cores.
Are you interested in faint nebulae? Then try your luck with IC 59. One of two arc-shaped nebulae (the other is IC 63) that are associated with the extremely luminous star Gamma Cassiopeiae. IC 59 lies about 20′ to the north of Gamma Cas and is primarily a reflection nebula. Other faint emission nebulae include the “Heart and Soul” (LBN 667 and IC 1805) which includes wide open star clusters Collider 34 and IC 1848.
Of course, no trip through Cassiopeia would be complete without mentioning Tycho’s Star! Given the role this “new star” played in the history of astronomy (and as one of only 8 recorded supernovas that was visible with the naked eye), it is something no amateur astronomer or stargazer should pass up!
While there is no actual meteoroid stream associated with the constellation of Cassiopeia, there is a meteor shower which seems to emanate near it. On August 31st the Andromedid meteor shower peaks and its radiant is nearest to Cassiopeia. Occasionally this meteor shower will produce some spectacular activity but usually the fall rate only averages about 20 per hour. There can be some red fireballs with trails. Biela’s Comet is the associated parent with the meteor stream.
Welcome back to Constellation Friday! Today, we will be dealing with one of the best-known constellations, that crabby asterism known as “Cancer”!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of the then-known 48 constellations. His treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come. One of these constellations is Cancer, which is represented by “the Crab”.
In mythology, Cancer was part of the Twelve Labors of Hercules. While Hercules was busy fighting the multi-headed monster (Hydra), the goddess Hera – who did not like Hercules – sent the Crab to distract him. Cancer grabbed onto the hero’s toe with its claws, but was crushed by Hercule’s mighty foot. Hera, grateful for the little crustacean’s heroic sacrifice, gave it a place in the sky. Given that the crab did not win, the gods didn’t give it any bright stars.
History of Observation:
The first recorded examples of the Cancer constellation come from the 2nd millennium BCE, where it was known to Akkadian astronomers as the “Sun of the South”. This was most likely due to its position at the summer solstice during ancient antiquity. By classical antiquity, Cancer came to be called the “Gate of Men”, based on the beleif that it was the portal through which souls came and went from the heavens.
Given its relative faintness in the night sky, Cancer was often described as the “Dark Sign” throughout history. For instance, the medieval Italian poet Dante alluded to its faintness and position of Cancer in heavens as follows (in the Paradiso section of The Divine Comedy):
“Then a light among them brightened, So that, if Cancer one such crystal had, Winter would have a month of one sole day.”
Cancer’s stature as a constellation of the Zodiac has remained steadfast over the millennia, thought its position has changed. Over two thousand years ago, the sun shone in front of the constellation during the Northern Hemisphere’s summer solstice. Today, the Sun resides in front of the constellation Taurus when the summer solstice sun reaches its northernmost point.
Though comparatively faint, the Cancer constellation contains several notable stars. For starters, there is Beta Cancri, which is also known by the Arabic name of Al Tarf (“the eye” or “the glance”). Beta Cancri is the brightest star in Cancer and is about 660 times brighter than our Sun.
This K-class orange giant star is about 290 light years away from Earth, and is part of a binary system that includes a 14th magnitude star. This second star is so far away – about 65 times the distance of Pluto from the Sun – that their orbital period is at least 76,000 years!
Then there is Delta Cancri – an orange giant star approximately 180 light-years away. This is the second-brightest star in the Cancer constellation, and also where the famous Beehive Cluster (Messier 44) can be found (see below). It is also known by its Latin name of Asellus Australis, which means “southern donkey colt” (or “southern ass” if you’re feeling comedic!).
A bit further north is Gamma Cancri, an A-type white subgiant located 158 light years from Earth. Its Latin name is Asellus Borealis, which means (you guessed it!) “northern ass”. Both this star and Delta Cancri are significant because of their mythological connection and proximity to Messier 44.
Next up is Alpha Cancri, the fourth brightest star in the constellation, which is also known as Acubens. The star also goes by the names of Al Zubanah or Sertans, which are derived from the Arabic az-zub?nah (which means “claws”), while Sertan is derived from sara??n, which means “the crab.” Located approximately 174 light years from Earth, Alpha Cancris is actually a multiple star system – Alpha Cancri A and B (a white A-type dwarf and an 11th magnitude star, respectively.
Cancer is also home to many Deep Sky Objects. For instance, there is the aforementioned Beehive Cluster (Messier 44). This open cluster is the nearest of its type relative to our Solar System, and contains a larger star population than most other nearby clusters. Under dark skies the Beehive Cluster looks like a nebulous object to the unaided eye; thus it has been known since ancient times.
The classical astronomer Ptolemy called it “the nebulous mass in the heart of Cancer,” and it was among the first objects that Galileo studied with his telescope. The cluster’s age and proper motion coincide with those of the Hyades stellar association, suggesting that both share a similar origin. Both clusters also contain red giants and white dwarfs, which represent later stages of stellar evolution, along with main sequence stars of spectral classes A, F, G, K, and M.
So far, eleven white dwarfs have been identified, representing the final evolutionary phase of the cluster’s most massive stars, which originally belonged to spectral type B. Brown dwarfs, however, are extremely rare in this cluster, probably because they have been lost by tidal stripping from the halo.
Then there’s M67, which can be viewed due west of Alpha Cancri. M67 is not the oldest known galactic cluster, but there are very few in the Milky Way known to be older. M67 is an important laboratory for studying stellar evolution, since all its stars are at the same distance and age, except for approximately 30 anomalous blue stragglers, whose origins are not fully understood.
M67 has more than 100 stars similar to the Sun and many red giants, though the total star count has been estimated at over 500. The cluster contains no main sequence stars bluer than spectral type F, since the brighter stars of that age have already left the main sequence. In fact, when the stars of the cluster are plotted on the Hertzsprung-Russell diagram, there is a distinct “turn-off” representing the stars which are just about to leave the main sequence and become red giants.
It appears that M67 does not contain an unbiased sample of stars. One cause of this is mass segregation, the process by which lighter stars (actually, systems) gain speed at the expense of more massive stars during close encounters, which causes the lighter stars to be at a greater average distance from the center of the cluster or to escape altogether.
Then there’s NGC 2775, which is positioned some 60 million light years away. NGC 2775 is a peculiar blend of spiral galaxy with a smooth bulge in the center. The star formation is confined to this ring of tightly wound arms, and the galaxy has been the location of 5 supernovae explosions in the past 30 years!
Next up is DX Cancri, a faint, magnitude 14, cool red dwarf star that has less than 9% the mass of our Sun. It is a flare star that has intermittent changes in brightness by up to a five-fold increase. This star is far too faint to be seen with the naked eye, even though it is the 18th closest star system to the Sun at a distance of 11.82 light years, and is the closest star in the constellation Cancer.
Now set your mark on 55 Cancri (located at RA 8 52 35 Dec +28 19 59). Also known as Rho1 Cancri, this binary star system is located approximately 41 light-years away from Earth and has a whole solar system of its own! The system consists of a yellow dwarf star and a smaller red dwarf star, separated by over 1,000 times the distance from the Earth to the Sun.
As of 2007, five extrasolar planets have been confirmed to be orbiting the primary – 55 Cancri A (the yellow dwarf). The innermost planet is thought to be a terrestrial “super-Earth” planet, with a mass similar to Neptune, while the outermost planets are thought to be Jovian planets with masses similar to Jupiter.
As one of the 12 constellations along the ecliptic, Cancer is relatively easy to find with small telescopes and even binoculars. It lies in the second quadrant of the northern hemisphere (NQ2) and can be seen at latitudes between +90° and -60°. It occupies an area of 506 square degrees, making it the 31st largest constellation in the night sky.
There is only one meteor shower associated with the constellation of Cancer. The peak date for the Delta Cancrids is on or about January 16th. The radiant, or point of origin is just west of Beehive. It is a minor shower and the fall rate averages only about 4 per hour and the meteors are very swift.
Like all of the traditional constellations that belong to the Zodiac family, the significance of Cancer has not waned, despite the passage of several thousand years. Best of luck finding it, though you won’t need much!
Welcome back to constellation Friday! Today, in honor of our dear friend and contributor, Tammy Plotner, we examine the Aries constellation. Enjoy!
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of the then-known 48 constellations. His treatise, known as the Almagest, would serve as the authoritative source of astronomy for over a thousand years to come. Since the development of modern telescopes and astronomy, this list has come to be expanded to include the 88 constellation that are recognized by the International Astronomical Union (IAU) today.
Of these constellations, Aries – named in honor of the Ram from classical Greek mythology – is featured rather prominently. This faint constellation has deep roots, and is believed to date all the way back to the astrological systems of the ancient Babylonians. Positioned on the ecliptic plane, it is bordered by constellations of Perseus, Triangulum, Pisces, Cetus and Taurus, and is also the traditional home of the vernal equinox.
Did you know that there are 88 constellations in the night sky? Over the course of several thousand years, human beings have cataloged and named them all. But only 12 of them are particularly famous and continue to play an active role in our astrological systems. These are known as the zodiac signs, 12 constellations that correspond to the different months of the year.
Each of these occupies a sector of the sky which makes up 30° of the ecliptic, starting at the vernal equinox – one of the intersections of the ecliptic with the celestial equator. The order of these astrological signs is Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. Here are all the zodiac signs and their dates. If your birthday falls within one of those date ranges, that’s your zodiac sign.
Granted, modern science has shown astrology to be an ancient fallacy, a way of connecting patterns in celestial movements to events and behaviors here on Earth. But for ancient people, such patterns were necessary given the fact that they lacked an understanding of human psychology, astronomy, and that Earth was not the center of the universe.
The concept of the zodiac originated in Babylon in the 2nd millennium BCE, and was later influenced by Hellenistic (Ancient Greek), Roman, and Egyptian culture. This resulted in a mix of traditions, where the 12 zodiac symbols were associated with the 12 Houses – different fields of experience associated with the various planets – and the four classical elements (Earth, Wind, Water and Fire).
In essence, astrology maintains that celestial phenomena are related to human activity, so the signs are held to represent certain characteristics of behavior and personality traits. What we know today as astrology comes from the 2nd century AD, as it was formally described by Ptolemy in his work, Tetrabiblos.
This book was responsible for the spread of astrology’s as we know it across Europe and the Middle East during the time of the Roman Empire. These traditions have remained relatively unchanged for over seventeen centuries, though some alterations have been made due to the subsequent discoveries of the other planets in our Solar System.
Naturally, the birth of the modern psychology, biology and astronomy has completely discredited the notion that our personalities are determined by birth signs, the position of the stars or the planets. Given what we know today of the actual elements, the movements of the planets, and the forces that govern the universe, astrology is now known for being little more than superstition.
What’s more, the dates of the ‘star signs’ were assigned over 2,000 years ago, when the zodiac was first devised. At that time, astronomers believed that the Earth’s position was fixed in the universe, and did not understand that the Earth is subject to precession – where Earth’s rotational and orbital parameters slowly change with time. As such, the zodiac signs no longer correspond to constellations of stars that appear in night sky.
And last, but certainly not least, there is the issue of the missing 13th sign, which corresponds to the constellation Ophiuchus. Over 2000 years ago, this constellation was deliberately left out, though the Sun clearly passes in front of it after passing in front of Scorpius (aka. Scorpio) and before reaching Sagittarius.
It is unclear why ancient astrologers would do this, but it is a safe bet that they wanted to divide the 360° path of the Sun into 12 equal parts. But the true boundaries that divide the constellations, as defined by the International Astronomical Union (IAU), are not exact. And Ophiuchus actually spends more time behind the Sun than its immediate neighbor (19 days compared to Scorpius’ 12).
To find out what zodiac sign you were really born under, check out this story from BBC’s iWonder. And in the meantime, here are the zodiac signs, listed in order along with what they mean, and some interesting facts associated with their respective constellations:
Aries: March 21 – April 19
The sign of Aries, which covers 0° to 30° of celestial longitude, is represented by The Ram, which is based on the Chrysomallus – the flying ram that provided the Golden Fleece in Greek mythology. Aries is associated with the First House, known traditionally as Vita (Latin for life) and in the modern context as the “House of Self”. Aries is associated with Fire, and the ruling celestial body of Aries is Mars.
The Aries constellation is also home to Teegarden’s Star, one of Sun’s closest neighbors, located approximately 12 light years away. It appears to be a red dwarf, a class of low temperature and low luminosity stars. And then there’s Alpha Areitis, which is easily spotted by the naked eye. Also known as “Hamal” – literally “head of the sheep” in Arabic – this star is located at the point where constellations angles downward to form an arc.
For those with telescopes, several galaxies can be spotted within the Aries constellation as well. These include the spiral galaxy NGC 772 and the large 13th magnitude NGC 697 spiral galaxy. NGC 972 is another, which is faint (at magnitude 12) and part of a galaxy group. And then there’s the dwarf irregular galaxy NGC 1156, which is considered a Magellanic-type galaxy with a larger than average core.
Aries is also home to several meteor showers, such as the May Arietids. This daylight meteor shower begins between May 4th and June 6th with maximum activity happening on May 16th. The Epsilon Arietids are also a daylight occurrence, and are active between April 25th to May 27th with peak activity on May 9th. And then there are the Daytime Arietids, which occur from May 22nd to July 2nd with a maximum rate of one a minute on June 8th.
To top it off, the Aries constellation contains several stars with extrasolar planets. For example, HIP 14810, a G5 type star, is orbited by three confirmed exoplanets, all of them giant planets (all Super-Earths). HD 12661, also a G-type main sequence star, has two orbiting planets (which appear to be Super-Jupiters). And HD 20367, a G0 type star, has one orbiting gas giant that roughly the same size as Jupiter.
Taurus: April 20 – May 20
The sign of Taurus, which covers 30° to 60° of celestial longitude, is represented by The Bull – which is based on the Cretan Bull that fathered the Minotaur and was killed by Theseus. Taurus is associated with the Second House, known by the Latin name of Lucrum (wealth) and by the modern name, “House of Value”, and the element Earth. The ruling celestial body of Taurus is Venus.
Taurus’ brightest star, Alpha Tauri, is also known by its traditional name, Al Dabaran (which was Latinized to become Aldebaran). The name, which is Arabic, literally means “the Follower” because of the way the Taurus constellation appears to follow the Pleiades star cluster across the sky. In Latin, it was traditionally known as Stella Dominatrix, but to Medieval English astronomers, it was known as Oculus Tauri – literally the “eye of Taurus.”
There is one major annual meteor shower associated with the constellation of Taurus: the annual Taurids, which peak on or about November 5th of each year and have a duration period of about 45 days. The maximum fall rate for this meteor shower is about 10 meteors per hour, with many bright fireballs often occurring when the parent comet – Encke – has passed near perihelion.
And speaking of Pleiades (aka. Messier 45, The Seven Sisters) this cluster of stars is located perpendicular to Aldebaran in the night sky, and is visible to the unaided eye. Although it is made up of over 1000 confirmed stars, this object is identifiable by its seven particularly bright blue stars (though as many as 14 up can be seen with the naked eye depending on local observing conditions).
Gemini: May 21 – June 20
The sign Gemini covers 60° to 90° of the celestial longitude, and is represented by The Twins. These are based on the Dioscuri of Greek mythology, two mortals that were granted shared godhood after death. Gemini is part of the Third House, traditionally named Fratres (Brothers) and currently known as the House of Communications. The associated element for Geminis is Air, and the ruling celestial body is Mercury.
Gemini’s alpha and beta stars – aka. Castor and Pollux (“The Twins”) – are the easiest to recognize and can be spotted with the naked eye. Pollux is the brighter of the two, an orange-hued giant star of magnitude 1.2 that is 34 light-years from Earth. Pollux has an extrasolar planet revolving around it, as do two other stars in Gemini, a super-Jupiter which was confirmed in 2006.
There are two annual meteor showers associated with the constellation of Gemini. The first is the March Geminids, which peaks on or around March 22nd. The average fall rate is generally about 40 per hour (but this varies) and the meteors appear to be very slow, entering our atmosphere unhurriedly and leaving lasting trails.
The second meteor shower are the Geminids themselves, which peak on or near the date of December 14th, with activity beginning up to two weeks prior and lasting for several days. The Geminids are one of the most beautiful and mysterious showers, with a rate of about 110 per hour during a moonless night.
The Gemini constellation is also associated with Messier 35, a galactic open star cluster that is easily spotted with the naked eye. The star cluster is quite young, having formed some 100 million years ago, and is quite bright due to it having blown away most of its leftover material (i.e. nebular dust and gas) that went into the star formation process. Other open clusters in Gemini include NGC 2158, which lies directly southwest of M35 in the night sky.
Cancer: June 21 – July 22
Cancer, which covers 90° to 120° of celestial longitude, is represented by The Crab – or Karkinos, a giant crab from Greek mythology that harassed Hercules during his fight with the Hydra. The sign is associated with the Fourth House – Genitor (Parent) in Latin, or the House of Home and Family in modern times. In terms of the elements, Cancers are characterized by the element of Water, and the ruling celestial body of Cancer is The Moon.
Cancer’s best known star is Beta Cancri, also known by its Arab name Altarf (“the End”). This 3.5 magnitude star is located 290 light-years from Earth and is a binary star system that consists of a spectral type K4III orange giant and a magnitude 14 red dwarf. This system is also home to a confirmed exoplanet, beta Cancri b, which is a Super-Jupiter with an orbital period of over 600 days.
In terms of deep-sky objects, Cancer is best known as being the home of Messier Object 44 (aka. Praesepe, or the Beehive Cluster), an open cluster located in the center of the constellation. Located 577 light-years from Earth, it is one of the nearest open clusters to our Solar System. M44 contains about 50 stars, the brightest of which are of the sixth magnitude.
The smaller, denser open cluster of Messier Object 67 can also be found in Cancer, which is 2500 light-years from Earth and contains approximately 200 stars. And so can the famous quasar, QSO J0842+1835, which was used to measure the speed of gravity in the VLBI experiment conducted by Edward Fomalont and Sergei Kopeikin in September 2002.
The active galaxy OJ 287 is also found in the Cancer constellation. Located 3.5 billion light years away from Earth, this galaxy has a central supermassive black hole that is one of the largest known (with 18 billion solar masses), and produces quasi-periodic optical outbursts. There is only one meteor shower associated with the constellation of Cancer, which is the Delta Cancrids. The peak date for this shower is on or about January 16t, and has been known to average only about 4 comets per hour (and the meteors are very swift).
Leo: July 23 – Aug. 22
Those born under the sign of Leo, which covers 120° to 150° of celestial longitude, carry the sign of The Lion – which is based on the Nemean Lion of Greek mythology, a lion that had an impenetrable hide. The sign of Leo is tied to the Fifth House, known in Latin as Nati (Children), or by its modern name, House of Pleasure. The sign of Leo is also associated with the element of Fire and the ruling celestial body of Leo is The Sun.
There are five annual meteor showers associated with the constellation Leo. The first is the Delta Leonid meteor stream, which begins between February 5th through March 19th every year. The activity peaks in late February, and the maximum amount of meteors averages around 5 per hour. The next is the Sigma Leonid meteor shower, which begins on April 17th. This is a very weak shower, with activity rates no higher than 1 to 2 per hour.
The next is the November Leonids, the largest and most dependable meteor shower associated with the Leo constellation. The peak date is November 17th, but activity occurs around 2 days on either side of the date. The radiant is near Regulus and this is the most spectacular of modern showers.
The shower is made more spectacular by the appearance of the Temple-Tuttle comet, which adds fresh material to the stream when it is at perihelion. The last is the Leo Minorids, which peak on or about December 14th, which is believed to produce around 10 faint meteors per hour.
Leo is also home to some of the largest structures in the observable universe. This includes many bright galaxies, which includes the Leo Triplet (aka. the M60 group). This group of objects is made up of three spiral galaxies – Messier 65, Messier 66, and NGC 3628.
The Triplet is at a distance of 37 million light-years from Earth and has a somewhat distorted shape due to gravitational interactions with the other members of the Triplet, which are pulling stars away from M66. Both M65 and M66 are visible in large binoculars or small telescopes, but seeing them in all of their elongated glory requires a telescope.
In addition, it is also home to the famous objects Messier 95, Messier 96, and Messier 105. These are spiral galaxies, in the case of M95 and M96 (with M95 being a barred spiral), while Messier 105 is an elliptical galaxy which is known to have a supermassive black hole at its center. Then there is the Leo Ring (aka. Cosmic Horseshoe) a cloud of hydrogen and helium gas, that orbits two galaxies found within this constellation.
Virgo: Aug. 23 – Sept. 22
The sign of Virgo, which covers 150° to 180° of celestial longitude, is represented by the The Maiden. Based on Astraea from Greek mythology, the maiden was the last immortal to abandon Earth at the end of the Silver Age, when the gods fled to Olympus. Virgo is part of the Sixth House – Valetudo (Health) in Latin, or House of Health in modern times. They are also associated with the element of Earth and the ruling celestial body of Virgo is Mercury.
The brightest star in the Virgo constellation is Spica, a binary and rotating ellipsoidal variable – which means the two stars are so close together that they are egg-shaped instead of spherical – located between 240 and 260 light years from Earth. The primary is a blue giant and a variable star of the Beta Cephei type.
The star 70 Virginis was one of the first planetary systems to have a confirmed exoplanet discovered orbiting it, which is 7.5 times the mass of Jupiter. The star Chi Virginis has one of the most massive planets ever detected, at a mass of 11.1 times that of Jupiter. The sun-like star 61 Virginis has three planets: one is a super-Earth and two are Neptune-mass planets.
Libra: Sept. 23 – Oct. 22
The sign of Libra covers 180° to 210° of celestial longitude. It is represented by the symbol of The Scales, which is based on the Scales of Justice held by Themis, the Greek personification of divine law and custom and the inspiration for modern depictions of Lady Justice. Libra is part of the Seventh House – Uxor (Spouse) or House of Partnership, are associated with the element of Air, and the ruling celestial body is Venus.
Two notable stars in the Libra constellation are Alpha and Beta Librae – also known as Zubenelgenubi and Zubeneschamali, which translates to “The Southern Claw” and “The Northern Claw”. Alpha Libae is a double star consisting of an A3 primary star with a slight blue tinge and a fainter type F4 companion, both of which are located approximately 77 light years from our Sun.
Beta Librae is the brighter of the two, and the brightest star in the Virgo constellation. This is a blue star of spectral type B8 (but which appears somewhat greenish) which is located roughly 160 light years from Earth. Then there’s Gamma Librae (also called Zubenelakrab, which means “the Scorpion’s Claw”) which completes the Scorpion sign. It is an orange giant of magnitude 3.9, and is located 152 light-years from Earth.
Libra is home to the star Gliese 581, which has a planetary system consisting of at least 6 planets. Both Gliese 581 d and Gliese 581 g are considered to be some of the most promising candidates for life. Gliese 581 c is considered to be the first Earth-like exoplanet to be found within its parent star’s habitable zone. All of these exoplanets are of significance for establishing the likelihood of life outside of the Solar System.
Libra is also home to one bright globular cluster, NGC 5897. It is a fairly large and loose cluster, has an integrated magnitude of 9, and is located 40,000 light-years from Earth.
Scorpio: Oct. 23 – Nov. 21
The sign of Scorpio covers 210° to 240° of celestial longitude. Scorpio is represented by The Scorpion, which is based on Scorpius – a giant scorpion in Greek mythology sent by Gaia to kill Orion. Scorpio is part of the Eighth House – Mors (Death), known today as the House of Reincarnation – and is associated with the element of Water. Traditionally, the ruling celestial body of Scorpio was Mars, but has since become Pluto.
The Scorpius constellations includes many bright stars, the brightest being Alpha Scorpii (aka. Antares). The name literally means “rival of Mars” because of its distinct reddish hue. Other stars of note include Beta Scorpii (Acrab, or “the scorpion”), Delta Scorpii (Dschubba, or “the forehead”), Xi Scorpii (Girtab, also “the scorpion”), and Sigma and Tau Scorpii (Alniyat, “the arteries”).
Lambda Scorpii (Shaula) and Upsilon Scorpii (Lesath) – whose names both mean “sting”- mark the tip of the scorpion’s curved tail. Given their proximity to one another, Lambda Scorpii and Upsilon Scorpii are sometimes referred to as “the Cat’s Eyes”.
The Scorpius constellation, due to its position within the Milky Way, contains many deep-sky objects. These include the open clusters Messier 6 (the Butterfly Cluster) and Messier 7 (the Ptolemy Cluster), the open star cluster NGC 6231 (aka. Northern Jewel Box), and the globular clusters Messier 4 and Messier 80 (NGC 6093).
The constellation is also where the Alpha Scorpiids and Omega Scorpiids meteor showers take place. The Alphas begin on or about April 16th and end around May 9th, with a peak date of most activity on or about May 3rd. The second meteor shower, the Omega (or June) Scorpiids peaks on or about June 5th of each year. The radiant for this particular shower is closer to the Ophiuchus border and the activity rate on the peak date is high – with an average of about 20 meteors per hour and many reported fireballs.
Sagittarius: Nov. 22 – Dec. 21
The sign of Sagittarius covers 240° to 270° of celestial longitude and is represented by The Archer. This symbol is based on the centaur Chiron, who according to Greek mythology mentored Achilles in the art of archery. Sagittarius is part of the Ninth House – known as Iter (Journeys) or the House of Philosophy. Sagittarius’ associated element is Fire (positive polarity), and the ruling celestial body is Jupiter.
Stars of note in the Sagittarius constellation include Alpha Sagittarii, which is also known as Alrami or Rukbat (literally “the archer’s knee”). Then there is Epsilon Sagittarii (“Kaus Australis” or “southern part of the bow”), the brightest star in the constellation – at magnitude 1.85. Beta Sagittarii, located at a position associated with the forelegs of the centaur, has the traditional name Arkab, which is Arabic for “achilles tendon.”
The second-brightest star is Sigma Sagittarii (“Nunki”), which is a B2V star at magnitude 2.08, approximately 260 light years from our Sun. Nunki is the oldest star name currently in use, having been assigned by the ancient Babylonians, and thought to represent the sacred Babylonian city of Eridu. Then there’s Gamma Sagittarii, otherwise known as Alnasl (the “arrowhead”). This is actually two star systems that share the same name, and both stars are actually discernible to the naked eye.
The Milky Way is at its densest near Sagittarius, since this is the direction in which the galactic center lies. Consequently, Sagittarius contains many star clusters and nebulae. This includes Messier 8 (the Lagoon Nebula), an emission (red) nebula located 5,000 light years from Earth which measures 140 by 60 light years.
Though it appears grey to the unaided eye, it is fairly pink when viewed through a telescope and quite bright (magnitude 3.0). The central area of the Lagoon Nebula is also known as the Hourglass Nebula, so named for its distinctive shape. Sagittarius is also home to the M17 Omega Nebula (also known as the Horseshoe or Swan Nebula).
This nebula is fairly bright (magnitude 6.0) and is located about 4890 light-years from Earth. Then there’s the Trifid Nebula (M20 or NGC 6514), an emission nebula that has reflection regions around the outside, making its exterior bluish and its interior pink. NGC 6559, a star forming region, is also associated with Sagittarius, located about 5000 light-years from Earth and showing both emission and reflection regions (blue and red).
Capricorn: Dec. 22 – Jan. 19
The sign of Capricorn spans 270° to 300° of celestial longitude and is represented by the Mountain Sea-Goat. This sign is based on Enki, the Sumerian primordial god of wisdom and waters who has the head and upper body of a mountain goat, and the lower body and tail of a fish. The sign is part of the Tenth House – Regnum (Kingdom), or The House of Social Status. Capricorns are associated with the element Earth, and the ruling body body is Saturn.
The brightest star in Capricornus is Delta Capricorni, also called Deneb Algedi. Like other stars such as Denebola and Deneb, it is named for the Arabic word for “tail”, which in this case translates to “the tail of the goat’. Deneb Algedi is a eclipsing binary star with a magnitude of 2.9, and which is located 39 light-years from Earth.
Another bright star in the Capricorni constellation is Alpha Capricorni (Algedi or Geidi, Arabic for “the kid”), which is an optical double star (two stars that appear close together) – both o which are binaries. It’s primary (Alpha² Cap) is a yellow-hued giant of magnitude 3.6, located 109 light-years from Earth, while its secondary (Alpha¹ Cap) is a yellow-hued supergiant of magnitude 4.3, located 690 light-years from Earth.
Beta Capricorni is a double star known as Dabih, which comes from the Arabic phrase “the lucky stars of the slaughter” a reference to ritual sacrifices performed by ancient Arabs. Its primary is a yellow-hued giant star of magnitude 3.1, 340 light-years from Earth, while the secondary is a blue-white hued star of magnitude 6.1. Another visible star is Gamma Capricorni (aka. Nashira, “bringing good tidings”), which is a white-hued giant star of magnitude 3.7, 139 light-years from Earth.
Several galaxies and star clusters are contained within Capricornus. This includes Messier 30 (NGC 7099) a centrally-condensed globular cluster of magnitude 7.5. Located approximately 30,000 light-years from our Sun, it cannot be seen with the naked eye, but has chains of stars extending to the north that can be seen with a telescope.
And then there is the galaxy group known as HCG 87, a group of at least three galaxies located 400 million light-years from Earth. It contains a large elliptical galaxy, a face-on spiral galaxy, and an edge-on spiral galaxy. These three galaxies are interacting, as evidenced by the high amount of star formation in the face-on spiral, and the connecting stream of stars and dust between edge-on spiral and elliptical galaxy.
The constellation of Capricornus has one meteor shower associated with it. The Capricornid meteor stream peaks on or about July 30th and is active for about a week before and after, with an average fall rate is about 10 to 30 per hour.
Aquarius: Jan. 20 – Feb. 18
Aquarius, which spans 300° to 330° of celestial longitude, is represented by the Water Bearer. In ancient Greek mythology, Aquarius is Ganymede, the beautiful Phrygian youth who was snatched up by Zeus to become the cup-bearer of the Gods. Aquarius is part of the Eleventh House – Benefacta (Friendship), or House of Friendship, is associated with the element of Air. Traditionally, the ruling celestial body of Aquarius was Saturn, but has since changed to Uranus.
While Aquarius has no particularly bright stars, recent surveys have shown that there are twelve exoplanet systems within the constellation (as of 2013). Gliese 876, one of the nearest stars (15 light-years), was the first red dwarf start to be found to have a planetary system – which consists of four planets, one of which is a terrestrial Super-Earth. 91 Aquarii is an orange giant star orbited by one planet, 91 Aquarii b, a Super-Jupiter. And Gliese 849 is a red dwarf star orbited by the first known long-period Jupiter-like planet, Gliese 849 b.
Aquarius is also associated with multiple Messier objects. M2 (NGC 7089) is located in Aquarius, which is an incredibly rich globular cluster located approximately 37,000 light-years from Earth. So is the four-star asterism M73 (which refers to a group of stars that appear to be related by their proximity to each other). Then there’s the small globular cluster M72, a globular cluster that lies a degree and half to the west of M73.
Aquarius is also home to several planetary nebulae. NGC 7293, also known as the Helix Nebula, is located at a distance of about 650 light years away, making it the closest planetary nebula to Earth. Then there’s the Saturn Nebula (NGC 7009) so-named because of its apparent resemblance to the planet Saturn through a telescope, with faint protrusions on either side that resemble Saturn’s rings.
There are five meteor showers associated with the constellation of Aquarius. The Southern Iota Aquarids begin around July 1st and end around September 18th, with the peak date occurring on August 6th with an hourly rate of 7-8 meteors average. The Northern Iota Aquarids occur between August 11th to September 10th, their maximum peak occurring on or about August 25th with an average of 5-10 meteors per hour.
The Southern Delta Aquarids begin about July 14th and end around August 18th with a maximum hourly rate of 15-20 peaking on July 29th. The Northern Delta Aquarids usually begin around July 16th, and last through September 10th. The peak date occurs on or around August 13th with a maximum fall rate of about 10 meteors per hour.
Then there is the Eta Aquarid meteor shower, which begins about April 21th and ends around May 12th. It reaches its maximum on or about May 5th with a peak fall rate of up to 20 per hour for observers in the northern hemisphere and perhaps 50 per hour for observers in the southern hemisphere. Last, there is the March Aquarids, a daylight shower that may be associated with the Northern Iota Aquarid stream.
Pisces: Feb. 19 – March 20
The sign of Pisces covers 330° to 360° of celestial longitude and is represented by the The Fish. This symbol is derived from the ichthyocentaurs – a pair of centaurian sea-gods that had the upper body of a male human, the lower front of a horse, and the tail of a fish – who aided Aphrodite when she was born from the sea. Pisces is part of the Twelfth House of Carcer (Prison), or The House of Self-Undoing, and are associated with the element of Water. The ruling celestial body of Pisces is traditionally Jupiter, but has since come to be Neptune.
Beta Piscium, also known as Samakah (the “Fish’s Mouth”), is a B-class hydrogen fusing dwarf star in the Pisces constellation. Located 495 light years from Earth, this star produces 750 times more than light than our own Sun and is believed to be 60 million years old. The brightest star in the constellation, Eta Piscium, is a bright class B star that is located 294 years away from our Solar System.
This star is also known by its Babylonian name, Kullat Nunu (which translates to “cord of the fish”), the Arab name Al Pherg (“pouring point of water”), and the Chinese name Yòu Gèng – which means “Official in Charge of the Pasturing“, referring to an asterism consisting of Eta Piscium and its immediate neighbors – Rho Piscium, Pi Piscium, Omicron Piscium, and 104 Piscium.
And then there’s van Maanen’s Star (aka. Van Maanen 2) a white dwarf that is located about 14 light years from our Sun, making it the third closest star of its kind to our system (after Sirius B and Procyon B). Gamma Piscium is a yellow-orange giant star located about 130 light years away, and is visible with just binoculars.
The Pisces constellationis also home to a number of deep-sky objects. These include M74, a loosely-wound spiral galaxy that lies at a distance of 30 million light years from our Sun. It has many clusters of young stars and the associated nebulae, showing extensive regions of star formation. Also, there’s CL 0024+1654, a massive galaxy cluster that is primarily made up of yellow elliptical and spiral galaxies. CL 0024+1654 lies at a distance of 3.6 billion light-years from Earth and lenses the galaxy behind it (i.e. it creates arc-shaped images of the background galaxy).
Last, there the active galaxy and radio source known as 3C 31. Located at a distance of 237 million light-years from Earth, this galaxy has a supermassive black hole at its center. In addition to being the source of its radio waves, this black hole is also responsible for creating the massive jets that extend several million light-years in both directions from its center – making them some of the largest objects in the universe.
There is one annual meteor shower associated with Pisces which peaks on or about October 7 of each year. The Piscid meteor shower has a radiant near the Aries constellation and produces an average of 15 meteors per hour which have been clocked at speeds of up to 28 kilometers per second. As always, the meteoroid stream can begin a few days earlier and end a few days later than the expected peak and success on viewing depends on dark sky conditions.
Currently, the Vernal Equinox is currently located in Pisces. In astronomy, equinox is a moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system. Due to the precession of the equinoxes, the Vernal Equinox is slowly drifting towards Aquarius.
Astrology is a tradition that has been with us for thousands of years and continues to be observed by many people and cultures around the world. Today, countless people still consult their horoscope to see what the future has in store, and many more consider their birth sign to be of special significance.
And the fact that many people still consider it to be valid is an indication that superstitious and “magical” thinking is something we have yet to completely outgrow. But this goes to show how some cultural traditions are so enduring, and how people still like to ascribe supernatural powers to the universe.
We have a complete guide to all 88 constellations here at Universe Today. Research them at your leisure, and be sure to check out more than just the “zodiac sign” ones!
We also have a comprehensive list of all the Messier Objects in the night sky.
The zodiac represents the constellations that the Sun passes through in its apparent path across Earth’s sky. Because the Sun (and the planets) are all on about the same plane in the Solar System, they pass through the same constellations and at times, can even eclipse each other.
While traditionally the zodiac is considered to have 12 constellations, technically the Sun passes through 13, according to this NASA page. In order, the constellations are Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius and Ophiuchus.
The reason there are now 13 constellations that the Sun passes through is that the axis of the Earth has changed over the millennia. Earth’s axis precesses or moves in a cycle that takes about 26,000 years. Over time, this means the direction of north has changed with respect to the sky. Vega was the North Star several thousand years ago, and will become it again in about 13,000 years, according to NASA. Today, the North Star is Polaris.
Because different cultures see different shapes in the stars of the sky, the number of constellations varied in ancient definitions of the zodiac. It has been used in cultures ranging from Greece to Babylon to China to India. It should also be noted that the constellations are of different size, so the Sun does not spend the same amount of time in each.
The number of constellations was fixed at 12 when mathematics was added to astronomy, according to Encyclopedia Britannica. While we don’t know when the symbols were first used, the first known instance is in Greek manuscripts used during the late Middle Ages, the encyclopedia added. Briefly, according to the encyclopedia, these are what each of the constellations are:
Aries (the ram), which has no bright stars and traditionally governs the period from March 21 to April 19. In Greek mythology, it represents the ran with the golden fleece. Phrixus sacrificed a ram to Zeus (the chief god) after safely fleeing Thessaly to Colchis on its back. Jason (the chief of the Argonauts) later recovered the fleece.
Taurus (the bull), whose brightest star Aldebaran is the 14th-brightest in the sky. Also in Taurus are two bright star clusters (the Pleiades and the Hyades) and the Crab Nebula. It traditionally governs April 20 to May 20. In Greek mythology, Taurus represents the bull form that Zeus (the chief god) took upon to abduct Europa.
Gemini (the twins), whose brightest stars are Castor and Pollux. It’s the current location of the northern summer solstice, when the Sun reaches its highest point in the sky. It traditionally represents May 21 to June 21. In Greek mythology, the twins were gods who “succored shipwrecked sailors and received sacrifices for favorable winds,” the encyclopedia stated.
Cancer (the crab), which also has no bright stars but contains a prominent star cluster known as the Beehive (Praesepe). It traditionally governs June 22 to July 22. In Greek mythology, it refers to a crab that was crushed after pinching Heracles while he was fighting a hydra. Hera (an enemy of Heracles) rewarded the crab by immortalizing it in the sky.
Leo (the lion), whose brightest star is Regulus — sometimes called the “little king.” It traditionally governs July 23 to August 22 and in Greek mythology, represents a lion that Heracles killed.
Virgo (the virgin), whose brightest star is Spica — the 15th-brightest seen in Earth’s sky. It’s also known for the Virgo cluster of galaxies and the pulsar PSR 1257+12, where astronomers found the first confirmed extrasolar planets in 1992. It traditionally represents August 23 to September 22 and in Greek mythology, is associated with the harvest maiden (Persephone).
Libra, which has no bright stars. It traditionally governs Sept. 22 to Oct. 23 and is associated with balance or justice, such as with the Roman goddess Astraea.
Scorpius, whose brightest star Antares is known as the “rival of Mars” due to its red color and similar appearance to the Red Planet. It also contains Scorpius X-1, the brightest X-ray source in the sky. It traditionally governs Oct. 24 to Nov. 21 and in Greek mythology, refers to one of two legends. The first is said to be a scorpion that killed Orion, and the second refers to one that spooked horses being controlled by Phaeton as the young man was trying to drive the Sun.
Sagittarius (the archer), which contains a prominent radio source known as Sagitarrius A. It is considered to govern Nov. 22 to Dec. 21, and is considered a mounted archer in several cultures (starting with the Babylonians in the 11th century).
Capricornus (the goat), which has no bright stars. It traditionally governs Dec. 22 to Jan. 19. In Greek mythology, it is associated with the god Pan. He leaped into the water to get away from a monster called Typhon, just as Pan was changing shape. This made him a goat with a fish tail.
Aquarius (the water bearer), which has no bright stars. It is considered to rule over Jan. 20 to Feb. 18 and is traditionally associated with a man pouring water out of a jug. The symbolism likely arises from the Middle East, whose astronomers noted that the constellation rises with the rainy season.
Pisces (the fish), which has no bright stars. It traditionally rules over Feb. 19 to March 20 and in Greek mythology, refers to Aphrodite and Eros. They went into a river to avoid a monster called Typhon. Some versions of the myth say they changed into fish, while others say they rode fish to get away.
We don’t put much stock in astrology or horoscopes here at Universe Today, but there’s one thing related to the zodiac that’s all science and no superstition: zodiacal light, captured here in a gorgeous photo by astronomer Alan Fitzsimmons above ESO’s La Silla Observatory.
Created by sunlight reflected off fine particles of dust concentrated inside the plane of the Solar System, zodiacal light appears as a diffuse, hazy band of light visible in dark skies stretching away from a recently-set Sun (or before the Sun is about to rise).
The Moon is located just outside the frame of this picture, bathing the observatory in an eerie light that is reflected off the clouds below.
The La Silla Observatory is located at the outskirts of the Chilean Atacama Desert at an altitude of 2400 meters (7,900 feet). Like other observatories in this area, La Silla is located far from sources of light pollution and, like ESO’s Paranal Observatory, it has some of the darkest night skies on the Earth.
The dome in the foreground, just to the right, is the Swiss 1.2-metre Leonhard Euler Telescope named in honor of the famous Swiss mathematician Leonhard Euler (1707–83).