Astronomy

Andromeda

The Princess Tied to the Rock Routine

In this months focus on a constellation I hope to enlighten you about one of the less recognisable, though no less interesting, constellations now up in our winter skies. To many an amateur astronomer, and even to people only vaguely aware of what is "up there", the name Andromeda can mean only one thing - the great Andromeda Galaxy. It is our twin spiral galaxy in the Local Group of galaxies and our largest extra-galactic neighbour. Whilst the Andromeda Galaxy is indeed a stunning sight this article will try to highlight some of the other less well known objects that also lie in the constellation Andromeda.

At this time of the year Andromeda sits high overhead and stretches between the winged horse Pegasus and her mother and husband, the Queen Cassiopeia and Perseus. In legend Andromeda was the beautiful daughter of King Cepheus and Cassiopeia. She was condemed to be devoured by the sea-monster Cetus, sent by Poseidon who had been enraged by the boasting of Cassiopeia. Perseus, he of Gorgon killing fame, happened on Andromeda tied to a rock by the sea on his journey home. He slew the monster and rescued her and the two were married (though not before a nasty incident involving a Gorgon's head and her rather unfortunate former suitor, Phineus). Perseus and Andromeda went on to rule much of the ancient world and as a result Athena, on their deaths, placed them in the skies along with many other characters from their history.

Actually seeing the feminine figure of Andromeda takes a great deal more imagination than employed by the person who came up with the above tale. The star map shown here gives an idea of the extent of Andromeda, but for a casual observer (and for my purposes here) Andromeda consists of 4 particularly bright stars - alpha, beta, gamma and delta - and one less bright star - mu. Alpha is also one of the corner stars of the great square of Pegasus and the three march away from this point towards Perseus. In the map to the right Pegasus is off to the right and the bottom row of stars are (from right to left) alpha, delta, beta and gamma. A less cluttered star map can be found here at the SEDS page for Andromeda.

Stella Sights

Of the four stars noted above my favourite has to be gamma Andromadae. Also known as Almach, in one of the society scopes this resolves into a very nice double star with good contrast between the white-gold supergiant primary star (mag 2) and its blue secondary partner (mag 5). Further investigation has gone on to show that Gamma Andromadae is in fact a 5-star system.

Mu Andromadae which splits off from the main run at Beta has a planetary system, with 3 planets already discovered orbiting it.

Beta Andromdae - whilst not in itself an exciting target, take a look at this star (called Mirach) and see if you can see its "ghost". The ghost is an elliptical galaxy, NGC 704, which looks to be a trick of the glare given off by Mirach, but is in fact a distant deep sky object. At mag 10.3 this object should be visible in the society scopes on a good deep sky night.

M31: The Andromeda Galaxy

Of course the highlight of any visit to Andromeda has to be the Andromeda Galaxy itself. On a good night in Durham this can be seen as a shimmering blur on the very edge of vision and in fact is the most distant object visible to the naked eye. The reason for this is its immensity (1.5 times the mass of the Milky Way) and its relative proximity to us at a down-to-the-chemists-like 2.5 million light years.

If we could see the full extent of this galaxy it would occupy as much space in the sky as 7 full moons. However because the stars are not tightly packed, with our equipment (eyes, binoculars or telescopes) we can only see the bright central region where the suspected Black Hole lurks. Still, this itself is a magnificent sight through a telescope - the bright region easy to see and the faint hint of more light stretching off beyond the eyepiece's field of view.

M32 and M110: Andromeda's Companions

Whilst viewing M31 through the telescope be sure to look out for M32 and M110. These are both dwarf elliptical galaxies which orbit the Andromeda Galaxy. This image, taken from the Deep Sky Survey, shows the positions of these two targets but ask an observation officer to identify them at the eye piece for you.

M110 is also the last entry in Messier's catalogue and was not in fact added by the great comet hunter himself (it is not known why he did not add this) - it was added in 1966 by Kenneth Jones.

NGC 7662 : The Blue Snowball

Lieing further away from the bright stars of Andromeda, NGC 7662, the Blue Snowball, is a planetary nebula, and one of the finest examples of such in the sky. In the society scopes it should be seen as small disc, distinctly un-star-like with a definite blue tinge. The Nexstar should be able to find this object as it can be a difficult one to hop to with a manual telescope like the 114.

A planetary nebula is formed when a star like our sun can no longer support itself through fusion reactions and collapses. Through gravitation and subsequent heating matter is then blown out to form an outer ring of gases. The remnant core then heats these gases up so that they glow. They are called Planetary Nebulae because they look similar to early views of Neptune and Uranus when seen through a telescope.

NGC 752 : An Open Cluster

This is a bright, but fairly scattered open cluster of stars. Located close to Almach, this is an easy object to find with the binoculars or a telescope. It contains around 80 stars and is thought to be in the region of 1.1 billion years old - old for an open cluster.

NGC 891 : The Outer Limits Galaxy

Named after an appearance in the opening titles of a TV show called the Outer Limits this will be a challenging object for the society scopes. As can be seen from the Deep Sky Survey image shown to the right, it is a very fine, edge-on spiral galaxy and with a listed visual magnitude of 10 should be visible with the Nexstar. It is located beyond Almach towards Perseus.

This concludes my brief look at the constellation Andromeda. As you can see it is a constellation with an interesting range of objects and I hope the society scopes will be turned in its direction over the coming weeks. I also hope this article has encouraged you to look beyond the obvious (c.f The Andromeda Galaxy) to the many other wonders that fill the sky above us.

Clear skies!

Nick Bramhall

November 2005