The Carina Constellation

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 these constellations, known as Argo Navis, would eventually be divided into three asterism  – one of which became the southern constellations of Carina. Bordered by the Vela, Puppis, Pictor, Volans, Chamaeleon, Musca and Centaurus constellations, Carina is one of 88 modern constellations that are currently recognized by the IAU.

Name and Meaning:

The stellar southern constellation Carina is part of the ancient constellation known as Argo Navis. It is now abbreviated and represents the “Keel”. While Carina has no real mythological connection, since its stars weren’t visible to the ancient Greeks and Romans, it does have a fascinating history. Argo Navis (or simply Argo) was a large southern constellation representing the Argo, the ship used by Jason and the Argonauts in Greek mythology.

Johannes Hevelius’ Argo Navis from Uranographia (1690). Credit: NASA/Chandra/Harvard University

The Argo was built by the shipwright Argus, and its crew were specially protected by the goddess Hera. The best source for the myth is the Argonautica by Apollonius Rhodius. According to a variety of sources of the legend, the Argo was said to have been planned or constructed with the help of Athena.

According to other legends it contained in its prow a magical piece of timber from the sacred forest of Dodona, which could speak and render prophecies. After the successful journey, the Argo was consecrated to Poseidon in the Isthmus of Corinth. It was then translated into the sky and turned into the constellation of Argo Navis. The abbreviation for it was “Arg”, and the genitive was “Argus Navis”.

History of Observation:

Carina is the only one of Ptolemy’s list of 48 constellations that is no longer officially recognized as a constellation. In 1752, French astronomer Nicolas Louis de Lacaille subdivided Argo Navis into Carina (the keel of the ship), Puppis (the Poop deck), and Vela (the sails). Were this still considered to be a single constellation, it would be the largest of all, being larger than Hydra.

When Argo Navis was split, its Bayer designations were also split. Whereas Carina got the Alpha, Beta and Epsilon stars, Vela got Gamma and Delta, Puppis got Zeta, and so on. The constellation Pyxis occupies an area which in antiquity was considered part of Argo’s mast. However, Pyxis is not typically considered part of Argo Navis, and in particular its Bayer designations are separate from those of Carina, Puppis and Vela.

Canopus (alpha Carinae), the brightest star in the Carina constellation and the second brightest star in the night sky. Credit: NASA

Notable Features:

The Carina constellation consists of 9 primary stars and has 52 Bayer/Flamsteed designated stars. It’s alpha star, Canopus, is not only he brightest star in the constellation, but the second brightest in the night sky (behind Sirius). This F-type giant is 13,600 times brighter than our Sun, with an apparent visual magnitude of -0.72 and an absolute magnitude of -5.53.

The name is the Latinized version of the Greek name Kanobos, presumably derived from the pilot of the shop that took Menelaus of Sparta to Troy to retrieve Helen in The Iliad. It is also known by its Arabic name, Suhail, which is derived from the Arabic name for several bright stars.

Before the launching of the Hipparcos satellite telescope, distance estimates for the star varied widely, from 96 light years to 1200 light years. Had the latter distance been correct, Canopus would have been one of the most powerful stars in our galaxy. Hipparcos established Canopus as lying 310 light years (96 parsecs) from our solar system; this is based on a parallax measurement of 10.43 ± 0.53 mas.

The difficulty in measuring Canopus’ distance stemmed from its unusual nature. Canopus is too far away for Earth-based parallax observations to be made, so the star’s distance was not known with certainty until the early 1990s. Canopus is 15,000 times more luminous than the Sun and the most intrinsically bright star within approximately 700 light years.

Sky as seen from central South America showing the approximate location of the new comet on August 19 in Puppis near the bright star Canopus. Credit: Stellarium

For most stars in the local stellar neighborhood, Canopus would appear to be one of the brightest stars in the sky. Canopus is outshone by Sirius in our sky only because Sirius is far closer to the Earth (8 light years). Its surface temperature has been estimated at 7350 ± 30 K and its stellar diameter has been measured at 0.6 astronomical units 65 times that of the sun.

If it were placed at the centre of the solar system, it would extend three-quarters of the way to Mercury. An Earth-like planet would have to lie three times the distance of Pluto! Canopus is part of the Scorpius-Centaurus Association, a group of stars which share similar origins.

Next up is Miaplacidus (beta Carinae), an A-type subgiant located approximately 111 light years from Earth. It is the second brightest star in the constellation and the 29th brightest star in the sky. The star’s name means “placid waters”, which is derived from the combination of the Arabic word for waters (miyah) and the Latin word for placid (placidus).

Then there’s Eta Carinae, a luminous blue variable (LBV) binary star that is between 7,500 and 8,000 light years distant from Earth. The combined luminosity of this system is four million times that of our Sun, and the most massive star in the system has between 120 and 250 Solar Masses. It is sometimes known by its traditional names, Tseen She (“heaven’s altar” in Chinese) and Foramen.

Eta Carinae, one of the most massive stars known. Image credit: NASA
Eta Carinae, one of the most massive stars in the known Universe. Credit: NASA

Also, it is believed that Eta Carinae will explode in the not-too-distant future, and it will be the most spectacular supernovae humans have ever seen. This supernova (or hypernova) might even affect Earth, since the star is only 7,500 light years away, causing disruption to the upper layers of the atmosphere, the ozone layer, satellites, and spacecraft could be damaged and any astronauts who happen to be in space could be injured.

Avior (epsilon Carinae) is another double star system, consisting of a K0 III class orange giant and a hot hydrogen-fusing B2 V  blue dwarf. With an apparent magnitude of 1.86 and is 630 light years distant, it is the 84th brightest star in the sky.  The name Avior was assigned in the late 1930s by Her Majesty’s Nautical Almanac Office as a navigational aid, at the request of the Royal Air Force.

Aspidiske (aka. Iota Carinae) is a rare spectral type A8 Ib white supergiant located 690 light years from Earth. With a luminosity of 4,900 Suns (and seven Solar Masses), it is the 68th brightest star in the sky and is estimated to be around 40 million years old. It is known by the names Aspidiske, Turais and Scutulum, all diminutives of the word “shield,” (in Greek, Arabic and Latin, respectively).

Since the Milky Way runs through Carina, there are a large number of Deep Sky Objects associated with it. For instance, there’s the Carina Nebula (aka. the Eta Carinae Nebula, NGC 3372), a large nebula surrounding the massive stars Eta Carinae and HD 93129A. In addition to being four time as bright as the Orion Nebula (Messier 42), it is one of the largest diffuse nebulae known.

The Eta Carinae Nebula, one of the largest nebulae in the known Universe. Credit: ESO, IDA, Danish 1.5 m, R. Gendler, J-E. Ovaldsen, C. Thöne, and C. Feron

The nebula is between 6,500 and 10,000 light years from Earth, and has an apparent visual magnitude of 1.0. It contains several O-type stars (extremely luminous hot, bluish stars, which are very rare). The first recorded observation of this nebula was made by the French astronomer Nicolas Louis de Lacaille in 1751-52, who observed it from the Cape of Good Hope.

The Carina Nebula contains two smaller nebulae – the Homunculus Nebula and the Keyhole Nebula. The Keyhole Nebula – a small, dark cloud of dust and with bright filaments of fluorescent gas, was named by John Herschel in the 19th century. It is about seven light years in diameter, and appears contrasted against the bright nebula in the background.

The Homunculus Nebula (Latin for “Little Man”) is an emission nebula embedded within the Eta Carinae Nebula, immediately surrounding the star Eta Carinae. The nebula is believed to have formed after an enormous outburst from the star, which coincided with Eta Carinae becoming the second brightest star in the night sky. The light of this outburst was visible from Earth by 1841.

There’s also the Theta Carinae Cluster (aka. the Southern Pleiades, because of its resemblance to the Pleiades cluster. This open cluster was discovered by Lacaille in 1751,  is located approximately 479 light years from Earth and is visible to the naked eye. The brightest star in the cluster, as the name indicates, is Theta Carinae, a blue-white dwarf.

The Keyhole Nebula, part of the larger Carina Nebula. Credit: NASA/The Hubble Heritage Team (AURA, STScI)

Then there’s the Wishing Well Cluster (aka. NGC 3532), an open cluster in Carina. Approximately 1,321 light years distant, the cluster is composed of about 150 stars that appear through a telescope like silver coins twinkling at the bottom of a wishing well. The cluster lies between the constellation Crux (the Southern Cross) and the False Cross asterism in Carina and Vela, and was first object observed by the Hubble Space Telescope in May 1990.

Finding Carina:

Carina is the 34th largest constellation in the sky, occupying an area of 494 square degrees. It lies in the second quadrant of the southern hemisphere (SQ2) and is visible at latitudes between +20° and -90° and is best seen during the month of March. Before you even begin with a telescope or binoculars, be sure to stop and just take a good look at Alpha Carinae – Canopus.

Canopus is essentially white when seen with the naked eye (though F-type stars are sometimes listed as “yellowish-white”). The spectral classification for Canopus is F0 Ia (Ia meaning “bright supergiant”), and such stars are rare and poorly understood; they are stars that can be either in the process of evolving to or away from red giant status. This in turn made it difficult to know how intrinsically bright Canopus is, and therefore how far away it might be.

Since the Milky Way runs through Carina, there are a large number of open clusters in the constellation, making it a binocular observing paradise. NGC 2516 is a magnitude 3.1 open cluster originally discovered by Abbe Lacaille in 1751 with a 1/2″ spyglass. This gorgeous 30 arc minute spread of stars is also known as Caldwell 96 and graces many observing lists, including the Astronomical League Open Cluster, Deep Sky and Southern Observing Clubs.

Location of the Carina Constellation in the southern skies. Credit: IAU/Sky&Telescope magazine

It is commonly known as the “Southern Beehive Cluster” (for it does resemble northern Messier 44) and it contains about 100 stars the brightest of which is an fifth magnitude red giant that lies near the center. As far as stellar age goes, this star cluster is very young – only about 140 million years old!

Now hop to IC 2602, popularly known as the “Southern Pleiades” for is resemblance to northern Messier 45. This galactic cluster contains more than 50 stars and is approximately 500 light years away from Earth. At its heart is blue-white star Theta Carinae, and it can be found by forming a triangle in the sky with Beta and Iota Carinae. With a stellar magnitude of 2.0, this object is easily seen as a nebulous patch to the unaided eye!

Another nebula that can been seen unaided but is better in binoculars is the Homunculus, an emission nebula surrounding the massive star Eta Carinae. The nebula is embedded within a much larger H II region, the Eta Carinae Nebula. Even though Eta Carinae is about 7,500 light-years away, structures only 10 billion miles across (about the diameter of our solar system) can be distinguished.

Dust lanes, tiny condensations, and strange radial streaks all appear with unprecedented clarity. Excess violet light escapes along the equatorial plane between the bipolar lobes. While there is relatively little dusty debris between the lobes down by the star; most of the blue light is able to escape. The lobes, on the other hand, contain large amounts of dust which absorb blue light, causing the lobes to appear reddish.

The gas pillar in the Carina Nebula, known as the “Mystic Mountain”. Credit: NASA/ESA/M. Livio and the Hubble 20th Anniversary Team (STScI)

The Eta Carinae Nebula, or NGC 3372 itself is fascinating. It is a hypergiant luminous blue variable star in the Carina constellation, one of the most massive stars yet discovered. Because of its mass and the stage of life, it is expected to explode in a supernova in the “near” future. Stars in the stellar mass class of Eta Carinae, with more than 100 times the mass of the Sun, produce more than a million times as much light as the Sun.

They are quite rare — only a few dozen in a galaxy as big as the Milky Way. They are assumed to approach (or potentially exceed) the Eddington limit, i.e., the outward pressure of their radiation is almost strong enough to counteract gravity. Stars that are more than 120 solar masses exceed the theoretical Eddington limit, and their gravity is barely strong enough to hold in their radiation and gas.

Now hop just three degrees away to NGC 3532 – known as the “Wishing Well Cluster”. This open star cluster is one of the jewels of the southern sky and is also referred to as Caldwell 91 and is on many observing lists. Want another? Try globular cluster NGC 2808, also known as Bennett 41. Beautiful NGC 2808 is a fine example of a symmetrical and strongly compressed globular cluster.

Viewable in binoculars and totally resolvable in a 6″ telescope, this is another of Dreyer’s remarkable objects described as very large extremely rich, and gradually reaching an extremely condensed status in the middle. NGC 2808 contains thousands of magnitude 13-15 stars!

The NGC 2808 star cluster, Credit: NASA, ESA, A. Sarajedini (University of Florida) and G. Piotto (University of Padova)

For double star fans, take on Epsilon Carinae, also known by the name Avior. Epsilon Carinae is a binary star located 630 light years away from our solar system. The primary component is a dying orange giant of spectral class K0 III, and the secondary is a hot hydrogen-fusing blue dwarf of class B2 V. The stars regularly eclipse each other, leading to brightness fluctuations on the order of 0.1 magnitudes.

Now try Upsilon Carinae – part of the Diamond Cross asterism in southern Carina. It’s name is Vathorz Prior, a name of Old Norse-Latin origin meaning “Preceding One of the Waterline”. Located approximately 1623 light years from Earth, the star system is made of two components. Upsilon Carinae A, is a white A-type supergiant with an apparent magnitude of +3.01 while its companion, Upsilon Carinae B, is a blue-white B-type giant 5 arc seconds away.

But no constellation would be complete without a true telescope challenge. Planetary nebula NGC 3211 (RA 10h 17m 50.4s Dec -62° 40´ 12″) heralds in at about 12th magnitude. For even more fun, try NGC 2867 (R.A. 09h 21m 25.3s Dec. -58° 18′ 40.7″). You’ll find it about a degree north/northeast of Iota. Iota Carinae. NGC 2867 may be no more than 2,750 years old.

Strangely, it is one of only a few dozen objects known to have a Wolf-Rayet star (type WC6) as its central star. NGC 2867 was discovered by John Herschel from Felhausen observatory at the Cape of Good Hope on April’s Fools Day, 1834 – appropriate since Herschel was almost fooled into thinking it was a new planet. Its size and appearance were certainly planet-like and it was only after careful checking that Herschel was convinced it was a nebula.

The NGC 3247 nebur. Credit NASA/JPL-Caltech/E. Churchwell (University of Wisconsin)

Now try NGC 3247 (RA 10 : 25.9 Dec -57 : 56 ). This is a very cool, very small galactic cluster with associated nebulosity. At around magnitude 8, you won’t find the rich little cluster much of a problem, but use minimal magnifcation to appreciate the true field!

While at the telescope, also look up NGC 3059 (9 : 50.2 Dec -73 : 55). Now, we’ve got a spiral galaxy cutting its way through the dust of the Milky Way! With an apparent magnitude of 12, and a 3.2 arc minute diameter, this barred spiral galaxy is going to present a nice, unique challenge to southern hemisphere observers.

There are myriad other things to look at in Carina as well, so don’t see this lovely constellation short! There is also a meteor shower associated with the constellation of Carina, too. The Eta Carinids are a lesser known meteor shower lasting from January 14 to 27 each year. The activity peaks on or about January 21. It was first discovered in 1961 in Australia. Roughly two to three meteors occur per hour at its maximum. It gets its name from the radiant which is close to the nebulous star Eta Carinae.

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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What Are The Most Famous Stars?

While there are untold billions of celestial objects visible in the nighttime sky, some of them are better known than others. Most of these are stars that are visible to the naked eye and very bright compared to other stellar objects. For this reason, most of them have a long history of being observed and studied by human beings, and most likely occupy an important place in ancient folklore.

So without further ado, here is a sampling of some of the better-known stars in that are visible in the nighttime sky:

Polaris:
Also known as the North Star (as well as the Pole Star, Lodestar, and sometimes Guiding Star), Polaris is the 45th brightest star in the night sky. It is very close to the north celestial pole, which is why it has been used as a navigational tool in the northern hemisphere for centuries. Scientifically speaking, this star is known as Alpha Ursae Minoris because it is the alpha star in the constellation Ursa Minor (the Little Bear).

The Polaris star system, as seen within the Ursa Minor constellation and up close. Credit: NASA, ESA, N. Evans (Harvard-Smithsonian CfA), and H. Bond (STScI)
The Polaris star system, as seen within the Ursa Minor constellation and up close. Credit: NASA, ESA, N. Evans (Harvard-Smithsonian CfA), and H. Bond (STScI)

It’s more than 430 light-years away from Earth, but its luminosity (being a white supergiant) makes it highly visible to us here on Earth. What’s more, rather than being a single supergiant, Polaris is actually a trinary star system, comprised of a main star (alpha UMi Aa) and two smaller companions (alpha UMi B, alpha UMi Ab). These, along with its two distant components (alpha UMi C, alpha UMi D), make it a multistar system.

Interestingly enough, Polaris wasn’t always the north star. That’s because Earth’s axis wobbles over thousands of years and points in different directions. But until such time as Earth’s axis moves farther away from the “Polestar”, it remains our guide.

Because it is what is known as a Cepheid variable star – i.e. a star that pulsates radially, varying in both temperature and diameter to produce brightness changes – it’s distance to our Sun has been the subject of revision. Many scientific papers suggest that it may be up to 30% closer to our Solar System than previously expected – putting it in the vicinity of 238 light years away.

Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King
Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King

Sirius:
Also known as the Dog Star, because it’s the brightest star in Canis Major (the “Big Dog”), Sirius is also the brightest star in the night sky. The name “Sirius” is derived from the Ancient Greek “Seirios“, which translates to “glowing” or “scorcher”. Whereas it appears to be a single bright star to the naked eye, Sirius is actually a binary star system, consisting of a white main-sequence star named Sirius A, and a faint white dwarf companion named Sirius B.

The reason why it is so bright in the sky is due to a combination of its luminosity and distance – at 6.8 light years, it is one of Earth’s nearest neighbors. And in truth, it is actually getting closer. For the next 60,000 years or so, astronomers expect that it will continue to approach our Solar System; at which point, it will begin to recede again.

In ancient Egypt, it was seen as a signal that the flooding of the Nile was close at hand. For the Greeks, the rising of Sirius in the night sky was a sign of the”dog days of summer”. To the Polynesians in the southern hemisphere, it marked the approach of winter and was an important star for navigation around the Pacific Ocean.

Alpha Centauri System:
Also known as Rigel Kent or Toliman, Alpha Centauri is the brightest star in the southern constellation of Centaurus and the third brightest star in the night sky. It is also the closest star system to Earth, at just a shade over four light-years. But much like Sirius and Polaris, it is actually a multistar system, consisting of Alpha Centauri A, B, and Proxima Centauri (aka. Centauri C).

Artist’s impression of the planet around Alpha Centauri B. Credit: ESO
Artist’s impression of the planet around Alpha Centauri B. Credit: ESO

Based on their spectral classifications, Alpha Centauri A is a main sequence white dwarf with roughly 110% of the mass and 151.9% the luminosity of our Sun. Alpha Centauri B is an orange subgiant with 90.7% of the Sun’s mass and 44.5% of its luminosity. Proxima Centauri, the smallest of the three, is a red dwarf roughly 0.12 times the mass of our Sun, and which is the closest of the three to our Solar System.

English explorer Robert Hues was the first European to make a recorded mention of Alpha Centauri, which he did in his 1592 work Tractatus de Globis. In 1689, Jesuit priest and astronomer Jean Richaud confirmed the existence of a second star in the system. Proxima Centauri was discovered in 1915 by Scottish astronomer Robert Innes, Director of the Union Observatory in Johannesburg, South Africa.

In 2012, astronomers discovered an Earth-sized planet around Alpha Centauri B. Known as Alpha Centauri Bb, it’s close proximity to its parent star likely means that it is too hot to support life.

Betelgeuse:
Pronounced “Beetle-juice” (yes, the same as the 1988 Tim Burton movie), this bright red supergiant is roughly 65o light-year from Earth. Also known as Alpha Orionis, it is nevertheless easy to spot in the Orion constellation since it is one of the largest and most luminous stars in the night sky.

Betelgeuse, as seen by the Hubble Space Telescope. Credit: NASA
Betelgeuse, as seen by the Hubble Space Telescope, and in relation to the Orion constellation. Credit: NASA

The star’s name is derived from the Arabic name Ibt al-Jauza’, which literally means “the hand of Orion”. In 1985, Margarita Karovska and colleagues from the Harvard–Smithsonian Center for Astrophysics, announced the discovery of two close companions orbiting Betelgeuse. While this remains unconfirmed, the existence of possible companions remains an intriguing possibility.

What excites astronomers about Betelgeuse is it will one day go supernova, which is sure to be a spectacular event that people on Earth will be able to see. However, the exact date of when that might happen remains unknown.

Rigel:
Also known as Beta Orionis, and located between 700 and 900 light years away, Rigel is the brightest star in the constellation Orion and the seventh brightest star in the night sky. Here too, what appears to be a blue supergiant is actually a multistar system. The primary star (Rigel A) is a blue-white supergiant that is 21 times more massive than our sun, and shines with approximately 120,000 times the luminosity.

Rigel B is itself a binary system, consisting of two main sequence blue-white subdwarf stars. Rigel B is the more massive of the pair, weighing in at 2.5 Solar masses versus Rigel C’s 1.9. Rigel has been recognized as being a binary since at least 1831 when German astronomer F.G.W. Struve first measured it. A fourth star in the system has been proposed, but it is generally considered that this is a misinterpretation of the main star’s variability.

Rigel A is a young star, being only 10 million years old. And given its size, it is expected to go supernova when it reaches the end of its life.

Vega:
Vega is another bright blue star that anchors the otherwise faint Lyra constellation (the Harp). Along with Deneb (from Cygnus) and Altair (from Aquila), it is a part of the Summer Triangle in the Northern hemisphere. It is also the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere (after Arcturus).

Characterized as a white dwarf star, Vega is roughly 2.1 times as massive as our Sun. Together with Arcturus and Sirius, it is one of the most luminous stars in the Sun’s neighborhood. It is a relatively close star at only 25 light-years from Earth.

Vega was the first star other than the Sun to be photographed and the first to have its spectrum recorded. It was also one of the first stars whose distance was estimated through parallax measurements, and has served as the baseline for calibrating the photometric brightness scale. Vega’s extensive history of study has led it to be termed “arguably the next most important star in the sky after the Sun.”

Artist's concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around the star Vega. Credit: NASA/JPL/Caltech/T. Pyle (SSC)
Artist’s concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around the star Vega. Credit: NASA/JPL/Caltech/T. Pyle (SSC)

Based on observations that showed excess emission of infrared radiation, Vega is believed to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk. For this reason, stars that display an infrared excess because of circumstellar dust are termed “Vega-like stars”.

Thousands of years ago, (ca. 12,000 BCE) Vega was used as the North Star is today, and will be so again around the year 13,727 CE.

Pleiades:
Also known as the “Seven Sisters”, Messier 45 or M45, Pleiades is actually an open star cluster located in the constellation of Taurus. At an average distance of 444 light years from our Sun, it is one of the nearest star clusters to Earth, and the most visible to the naked eye. Though the seven largest stars are the most apparent, the cluster actually consists of over 1,000 confirmed members (along with several unconfirmed binaries).

The core radius of the cluster is about 8 light years across, while it measures some 43 light years at the outer edges. It is dominated by young, hot blue stars, though brown dwarfs – which are just a fraction of the Sun’s mass – are believed to account for 25% of its member stars.

Pleiades by Jamie Ball
Pleiades, also known as M45, is a prominent open star cluster in the sky. Image Credit: Jamie Ball

The age of the cluster has been estimated at between 75 and 150 million years, and it is slowly moving in the direction of the “feet” of what is currently the constellation of Orion. The cluster has had several meanings for many different cultures here on Earth, which include representations in Biblical, ancient Greek, Asian, and traditional Native American folklore.

Antares:
Also known as Alpha Scorpii, Antares is a red supergiant and one of the largest and most luminous observable stars in the nighttime sky. It’s name – which is Greek for “rival to Mars” (aka. Ares) – refers to its reddish appearance, which resembles Mars in some respects. It’s location is also close to the ecliptic, the imaginary band in the sky where the planets, Moon and Sun move.

This supergiant is estimated to be 17 times more massive, 850 times larger in terms of diameter, and 10,000 times more luminous than our Sun. Hence why it can be seen with the naked eye, despite being approximately 550 light-years from Earth. The most recent estimates place its age at 12 million years.

A red supergiant, Antares is about 850 times the diameter of our own Sun, 15 times more massive, and 10,000 times brighter. Credit: NASA/Ivan Eder
A red supergiant, Antares is over 850 times the diameter of our own Sun, 15 times more massive, and 10,000 times brighter. Credit: NASA/Ivan Eder

Antares is the seventeenth brightest star that can be seen with the naked eye and the brightest star in the constellation Scorpius. Along with Aldebaran, Regulus, and Fomalhaut, Antares comprises the group known as the ‘Royal stars of Persia’ – four stars that the ancient Persians (circa. 3000 BCE) believed guarded the four districts of the heavens.

Canopus:
Also known as Alpha Carinae, this white giant is the brightest star in the southern constellation of Carina and the second brightest star in the nighttime sky. Located over 300 light-years away from Earth, this star is named after the mythological Canopus, the navigator for king Menelaus of Sparta in The Iliad. 

Thought it was not visible to the ancient Greeks and Romans, the star was known to the ancient Egyptians, as well as the Navajo, Chinese and ancient Indo-Aryan people. In Vedic literature, Canopus is associated with Agastya, a revered sage who is believed to have lived during the 6th or 7th century BCE. To the Chinese, Canopus was known as the “Star of the Old Man”, and was charted by astronomer Yi Xing in 724 CE.

An image of Canopus, as taken by crewmembers aboard the ISS. Credit: NASA
Image of Canopus, as taken by crew members aboard the ISS. Credit: NASA

It is also referred to by its Arabic name Suhayl (Soheil in persian), which was given to it by Islamic scholars in the 7th Century CE. To the Bedouin people of the Negev and Sinai, it was also known as Suhayl, and used along with Polaris as the two principal stars for navigation at night.

It was not until 1592 that it was brought to the attention of European observers, once again by Robert Hues who recorded his observations of it alongside Achernar and Alpha Centauri in his Tractatus de Globis (1592).

As he noted of these three stars, “Now, therefore, there are but three Stars of the first magnitude that I could perceive in all those parts which are never seene here in England. The first of these is that bright Star in the sterne of Argo which they call Canobus. The second is in the end of Eridanus. The third is in the right foote of the Centaure.”

This star is commonly used for spacecraft to orient themselves in space, since it is so bright compared to the stars surrounding it.

Universe Today has articles on what is the North Star and types of stars. Here’s another article about the 10 brightest stars. Astronomy Cast has an episode on famous stars.