Argo Navis – a giant constellation cut into three – to be observed during Festival of the Stars 29 & 30 May 2009

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The constellation Argo Navis as drawn by Johannes Hevelius and published in 1690

The basis of the constellations used by astronomers is the list of 48 classical constellations compiled by the Greek astronomer Ptolemy in the second century of our era. The largest of these is Argo Navis – the Ship Argo – that relates to the story of Jason and the Argonauts. The ship was called Argo after its builder Argus.

Jason was a Greek hero that had been raised by the Centaur (half-horse half-man) Chiron. His task along with his 50 or so Argonauts was to retrieve the Golden Fleece – if you want to know what the Golden Fleece was and the dragon that guarded it day and night, read the full details in Wikipedia.

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Eta Argus, now better known as Eta Carinae, pictured by Henry Chamberlain Russell of Sydney Observatory in 1891. Printed from the original negative plate as a very deep image by David Malin

One of the favourite celestial objects for Sydney Observatory director Henry Chamberlain Russell (1870-1905) was one he called Eta Argus. Today this object is better known as Eta Carinae and it consists of nebulosity surrounding a massive star also known as Eta Carinae, all at a distance of about 800 light years.

It is a little surprising that Russell still referred to Eta Argus as the giant constellation of Argo Navis had been divided into three over a century earlier.

French astronomer and abbé, Nicholas Louis de Laicaille, observed the southern stars from Cape Town in South Africa between 1750 and 1754. From his observations he prepared a catalogue of 10 000 southern stars and divided these into new constellations. He obviously considered Argo Navis as too unwieldy and divided it into three: Carina the Keel, Puppis the Poop Deck and Vela the Sails. These three constellations nicely keep the nautical flavour of the original constellation.

For his work Nicholas Louis de Lacaille has been honoured by a crater on the Moon being named after him. This crater is located in the south-central lunar highlands and can be seen around first quarter Moon.

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First quarter Moon with La Caille crater marked. Image Nick Lomb

During the two nights of the 2009 Festival of the Stars at Sydney Observatory the Moon will be almost at first quarter phase. Maybe it will be possible to view both the celestial delights of the old Argo Navis high in the southern sky and Lacaille’s crater on the Moon!

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