Argo Navis

Written by Pam Eastlick of the University of Guam.

Low on the southern horizon lies the crown jewel of spring equatorial skies. There are now six constellations among these stars. They are Puppis the Poop, Vela the Sails, Pyxis the Compass, Carina the Keel, Volans the Flying Fish and Columba the Dove. These six constellations are the dismembered parts of a much larger constellation outlined by the ancient Greeks. They called it the Great Ship Argo Navis.

Because of a phenomenon called precession, more southern stars were visible to the ancient sailors of the Mediterranean than are visible today. Low on their horizon, in spring skies, there appeared the apparition of a great ship. This ship sailed ever westward skimming along the southern horizon. The ancient Greeks said it was Argo Navis, the ship sailed by Jason and his Argonauts in search of the Golden Fleece.

The entire ship is not visible from the mainland U.S. You must travel south of 15 degrees North to see all of Carina the Keel and Volans the Flying Fish. The other four parts are visible in their entirety from the mainland U.S. If you are lucky enough to be able to see the whole ship, the easiest way to find it is to locate Canis Major, the Big Dog, Orion's hunting companion. The triangle of stars that form the dog's hind legs is your jumping-off point. There are two stars to the east and slightly north of the triangle. They are the top of the ship's high stern. The ship then sweeps down toward the southern horizon, virtually filling the southern sky with stars in the spring. The great ship is traditionally shown without a prow. This strange state of affairs is usually explained by the ship having lost its prow in the Clashing Rocks. However, the author H.A. Rey finds a perfectly good prow and figure-head in the ship's eastern end in his delightful and informative book "The Stars".

Puppis the Poop is the high stern of the Great Ship Argo Navis. The Milky Way runs right through the middle of this constellation, and Puppis contains many double and triple stars, 25 open clusters and several star-forming regions as well as condensations of stars in the Milky Way main body. Puppis also contains Puppis A, the remnant of a supernova that exploded about 4,000 years ago.

At right angles to the deck of the Great Ship Argo Navis there is a faint line of stars. This is Pyxis the Ship's Compass. Since no compass is a straight line, there are those who call Pyxis the Ship's Tiller. It was named by La Caille in the 1700's. He considered it separate from the ship. The Milky Way runs through the western edge of Pyxis and there are several open clusters in the constellation. Pyxis also contains T Pyxidis the most active of all known recurring novae. T Pyxidis brightens roughly every twenty years from its normal 14th magnitude to magnitude 6. Since the last maxima was in 1967, we're overdue for another.

Above the deck of the Great Ship Argo Navis is a ragged circle of stars. This is Vela the Ship's Sail, fully opened to catch the wind. Although many references call this constellation Vela the Sails, there appears to be only one sail. The Milky Way runs through Vela from northwest to southeast and Vela contains what appears to be the only complete break in the glowing band of light. This is called the Great Rift and it is caused by dark nebulae composed of dust and cold gas. Vela also contains many double and triple stars, several small star clusters and one of the most famous supernova remnants in the sky. The Vela supernova remnant, a large wispy filamentous nebula is all that remains of a star that blew itself into rather spectacular pieces about 12,000 years ago. It is as wide as ten full moons. Vela also contains part of the Gum Nebula, the largest nebula in the sky. The Gum Nebula has a diameter of about 30 degrees. There is speculation that the Gum Nebula glows because of the supernova explosion that produced the Vela supernova remnant.

Carina the Keel is the bottom of the Great Ship Argo Navis, and it can be seen in its entirety only from south of 15 degrees north. The Milky Way flows though the entire constellation and the whole area is full of many astounding deep sky objects. Carina also contains Canopus, the second brightest star in the sky. Canopus is not visible from most of the mainland U.S. and it reaches its highest point above the horizon in early evening skies in March. Canopus is the only star named for a real person (if you don't count Rotanev and Sualocin in Delphinus the Dolphin). He was the pilot of the Greek fleet of King Menelaus, and he sailed the ships to the destruction of Troy. Canopus is a blue-white super giant and its estimated distance is from 74 to 300 light years depending on which source you consult. Obviously, some distance measuring still needs to be done on southern hemisphere stars!

Carina also contains Eta Carinae. A century ago, Eta Carinae abruptly brightened to an apparent magnitude of -0.8 and was, briefly, the second brightest star in the sky. The star is now surrounded by a glowing nebula that makes viewing difficult but Eta Carinae appears to be one of the largest stars we know about, perhaps larger than the orbit of Saturn. Astronomers feel that Eta Carinae is very unstable and may soon become a supernova. Perhaps we'll see Eta Carinae become the brightest star in the sky in our lifetimes. Eta Carinae is associated with the diffuse nebula NGC 3372. NGC 3372 is about 300 light years across, over twenty times the Great Nebula in Orion. At 9,000 light years away it's over six times more distant than Orion's nebula. Perhaps someday, the Hubble Space Telescope will turn its cameras on this awesome star forming region.

Carina also contains NGC 2516, a beautiful globular cluster, best in binoculars and NGC 2808, a naked-eye globular cluster. The prow of the ship contains four stars that are often called the False Cross. From Guam's latitude (13 degrees North) these stars look more like a house roof viewed in perspective. The real Southern Cross is immediately to the east of Carina the Keel.

There are two animals associated with the Great Ship Argo Navis. One is Columba the Dove, forever leading the way westward for the ship. Columba can be viewed as either sitting on the stern of the ship or flying before it. Columba is easy to find, it lies just below Lepus the Hare, who in turn is lying at the feet of Orion the Hunter.

One of the stars just above the dove's head is Mu Columbae and it is one of three "runaway" stars. These stars (the others are AE Aurigae and 53 Arietis) are all fleeing the area of Orion's belt at incredible speeds. Mu Columbae is travelling at 72 miles per second! Astronomers think these three stars were scattered from a common point by a supernova explosion in a multiple star system.

Our sun is heading away from Columba as fast as it can go. Columba contains the "solar antapex" which is the opposite of the solar apex, which is the direction the sun is headed. Right now, we seem to be journeying toward the constellation Hercules.

The Great Ship Argo Navis also has another animal associated with it. This is Volans, the Flying Fish. Volans looks more like a kite headed for the ground (the way most of my kites go!), here on Guam than a sleek and slim flying fish. The kite's center contains NGC 2442 a rather lovely face-on spiral galaxy, but since Volans is too far south to contain any of the Milky Way, it doesn't have too many deep space objects. Volans was invented by Pieter Dirksz Keyser and Frederick de Houtman in the late 1500's.

The great ship Argo Navis has now been officially divided into four constellations. They are Puppis the Poop or stern of the ship, Vela the Sails (even though there only appears to be one); Pyxis the Ship's Compass (which more closely resembles a tiller); and Carina the Keel. The animals Columba the Dove and Volans the Flying Fish are also associated with this magnificent star group.

If you are lucky enough to see it in its entirety, find a dark clear sky and an unobstructed view to the south and watch the Great Ship Argo Navis glide silently on its endless voyage across the sky. After you have found the great ship and watched its silent sailing, turn your attention to that bright star low on the keel. That's Canopus the second brightest star in the sky. Here on Guam we enjoy skies that are virtually free of air pollution and relatively free of light pollution but no matter what your location or latitude, the stars are still out there. Turn off the T.V. tonight or tomorrow night and go outside to enjoy the evening's entertainment of your ancestors. Look up tonight, the universe awaits you!

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