The second asteroid ever discovered, the little studied Pallas, is at opposition this month. It will be dim this year, requiring a telescope or binoculars to be seen in the constellation of Cetus. Cetus, next door to Pisces and Aquarius, is in a part of the sky with many other watery constellations. It’s named for the sea monster slain by Perseus when he rescued Andromeda. Cetus had been terrorising the coast of Ethiopia at the request of Poseidon, after Andromeda’s mum Cassiopeia had insulted the sea nymphs. Andromeda was chained up to a rock in an attempt to appease the sea monster, when Perseus flew by and saved the maiden and the day!

Cetus and Pallas will be rising in the east after sunset, reaching their highest elevation in the south at about 2 am. Pallas is very dim, but once spotted, moves quite clearly against the background stars each night, passing below bright iota Cetus (the star at the tail of the whale) on September 29. Its dimness this year is due to its rather eccentric orbit – where eccentric is used in the mathematical sense of not round. At this opposition Pallas is nearly 300 million km from the Earth, whereas at a nearer opposition it might be only 184 million km away. February 2014 looks to be a good time to hunt for Pallas – it will be at one of the closest oppositions of the next few decades and so will be much brighter – at just less than seventh magnitude. This will still need binoculars! Pallas is also unusual in that its orbit is highly tilted with respect to the rest of the solar system. This means it can be seen quite far away from the ecliptic, well away from the signs of the Zodiac where we are used to seeing planets.

Pallas, HST image

Given this, it is just luck that Pallas was the second asteroid discovered. Ceres, number 1, was discovered in 1801. At the time Pallas was fairly near Ceres in the ecliptic. The German doctor and astronomer Henrich Olbers was checking for Ceres in 1802 when he discovered Pallas. Dr Olbers went on to discover the fourth asteroid Vesta a few years later. The first  asteroids were given female names – Pallas’ name comes from an alternate name for the goddess Athena. In some stories Athena killed her friend Pallas by accident and in mourning took her name as her own. The Palladium was the wooden statue of Pallas Athena that was stolen by Odysseus and Diomedes from Troy. With this sacred object gone, Troy then fell to the Greeks. This Palladium was taken back to Rome, where it was kept in the temple of Vesta. The chemical element Palladium is named for the asteroid – it was discovered in 1803.

Even though Olbers discovered Pallas and Vesta, he is rather better known for Olbers paradox. This asks “why is the sky dark?” In an infinite and eternal universe, every line of sight from the Earth should end up at a star; the sky should be bright! I’ll leave you to ponder that as you head outside to look for Cetus and Pallas in a dark sky…

This episode of “What is the Stars?” was first broadcast the week of September 17, 2012. Listen live Mondays and Fridays at 22:45 on RTÉ’s lyricfm