In the depths of the southern sky, where the stars appear brighter and more numerous, there once existed a constellation so vast and majestic that modern astronomers were forced to divide it.

In ancient times, sailors would look up to a sky studded with stars, identifying patterns that helped them navigate both the seas and their own mythologies. Among these celestial figures, one stood out for its size and splendor: Argo Navis, the stellar representation of the legendary ship on which Jason and the Argonauts embarked on their quest for the Golden Fleece.

This colossal constellation, which occupied nearly 28% more space in the sky than Hydra, the next largest constellation, was not purely a Greek creation. Its origins date back even further, to ancient Egypt, where it was known as the Boat of Osiris. Some scholars have even suggested connections to the Sumerian epic of Gilgamesh, although this theory lacks solid evidence.

The constellation Argo Navis, by Johann Bayer (1603)
The constellation Argo Navis, by Johann Bayer (1603). Credit: Public domain / Wikimedia Commons

Ptolemy, the 2nd-century Alexandrian astronomer, described it in his work Almagest, detailing how the constellation spanned a vast region of the Milky Way between Canis Major and Centaurus. With remarkable precision, Ptolemy identified stars that marked specific details of the ship, such as the “little shield”, the “rudder”, the “mast”, and the “stern ornaments”.

Aratus, the famous Greek poet-astronomer of the 3rd century B.C., noted that the constellation appeared to turn sternward, nautically reversed: Argo is dragged by the tail of the Great Dog, Canis Major; for its course is not a usual one, but it comes turned backward….

The magnitude of Argo Navis was not only visually impressive but also posed practical challenges for astronomers. With more than 160 stars easily visible to the naked eye, the constellation became difficult to manage in terms of cataloging and referencing. This problem persisted for centuries until, in 1763, French astronomer Nicolas Louis de Lacaille made a decision that would forever change celestial cartography.

The constellation Argo Navis and its three parts: Carina, Vela and Puppis.
The constellation Argo Navis and its three parts: Carina, Vela and Puppis. Credit: Kovayashi / Wikimedia Commons

Lacaille, recognizing the complexity of working with such an extensive constellation, proposed dividing Argo Navis into three parts: Carina (the keel), Puppis (the stern), and Vela (the sails). The bow was not represented in the constellation because, according to legend, it was the part that rotted away and fell on Jason, causing his death.

This division of the constellation was not immediately adopted by the entire astronomical community, and for almost two centuries, Argo Navis continued to exist in parallel with its constituent parts.

It wasn’t until 1930 that the International Astronomical Union officially formalized the division, marking the end of Argo Navis as a unified constellation. This act of “celestial dismantling” had fascinating consequences.

Carina Constellation
Carina Constellation. Credit: Till Credner / AlltheSky.com / Wikimedia Commons

For example, the brightest star of Argo Navis, Canopus, became alpha Carinae, the jewel of the Carina constellation. Canopus, the second-brightest star in the night sky after Sirius, is named after the navigator who piloted King Menelaus of Sparta’s ship during the Trojan War.

The fragmentation of Argo Navis also left curiosities in the star-naming system. The division respected the Bayer designation system, resulting in an unconventional distribution of Greek letters among the new constellations. Thus, Carina has alpha, beta, and epsilon; Vela has gamma and delta; while Puppis has zeta. This is a constant reminder of the original unity of these stars.

But the story of Argo Navis does not end with its division. In the following decades, astronomers have continued to study this region of the sky with renewed interest. Technological advances, such as space telescopes and radio telescopes, have enabled surprising discoveries in the areas once occupied by the great celestial ship.

Puppis Constellation
Puppis Constellation. Credit: Till Credner / AlltheSky.com / Wikimedia Commons

For example, in the Carina region, astronomers have identified the Carina Nebula, one of the most active and spectacular stellar nurseries in our galaxy. This vast cloud of gas and dust, stretching over 300 light-years, is home to some of the most massive and luminous stars known, including the volatile Eta Carinae, a hypergiant that could go supernova at any moment.

In Vela, researchers have discovered the remnants of a supernova that exploded about 11,000 years ago. These remnants, known as the Vela Remnant, are an invaluable source of information about stellar evolution and the processes that shape our universe.

Puppis, for its part, hosts numerous star clusters and nebulae, offering astronomers unique windows to study the formation and evolution of stars at different stages of their life cycles.

Vela Constellation
Vela Constellation. Credit: Till Credner / AlltheSky.com / Wikimedia Commons

For amateur stargazers in the Southern Hemisphere, the constellations that once formed the great ship remain an impressive sight. On clear, dark nights, far from the light pollution of cities, it is still possible to imagine the outline of Argo Navis majestically sailing along the celestial river of the Milky Way.

The precession of the equinoxes, a slow wobble of Earth’s axis that occurs over thousands of years, has caused the apparent position of these stars to shift southward. As a result, much of what was once Argo Navis is no longer easily visible from the Northern Hemisphere, adding a touch of mystery and exclusivity for those living in more southern latitudes.

This is the only constellation described by Claudius Ptolemy that is not currently recognized as a singular constellation. But, of course, that does not mean we cannot continue to contemplate it.

This article was first published on our Spanish Edition on September 5, 2024: Argo Navis, la antigua constelación que era tan grande que hubo que dividirla en tres

SOURCES

Ian Ridpath, Argo Navis, the ship Argo

Pam Eastlick, Argo Navis

John C. Barentine, The Lost Constellations: A History of Obsolete, Extinct, or Forgotten Star Lore

Morton Wagman, Lost Stars

Wikipedia, Argo Navis

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