What Can You See in the Night Sky This Week?

1 December 2011 by Philip James Ma...

Andromeda - the Milky Way’s twin galaxy - is the closest spiral galaxy to us. However, it’s still a long way away! If the Milky Way was the size of a 2p coin, Andromeda would be the size of another 2p coin just over half a metre away. And that’s our nearest neighbour! Unsurprisingly, the Andromeda galaxy is located in the constellation of Andromeda and can be seen from dusk till about 2:30am every night this week, writes Jas Virdee.

In Greek mythology Andromeda was a princess, daughter of Cepheus and Cassiopeia. Scientifically, Andromeda has a rich history. In the nineteenth century, objects in the night sky could only be broadly classified as “point-like” (i.e stars) or “diffuse” (extended and resolved). It was unclear whether these diffuse objects were clumps of cold gas and dust, or separate galaxies containing hundreds of billions of their own stars (so called “Island Universes” at the time). Many Astronomers were uncomfortable with the idea that some of these diffuse objects could be separate galaxies, because the distances involved were truly enormous.

Andromeda is 2.5 million light years away from us - which means that light takes 2.5 million years to get to here from there. When you look at Andromeda you are seeing light which is older than the human race. You could imaging the controversy that would have caused over a hundred years ago! The debate was finally settled by Curtis Olson, Ernest Opik and Edwin Hubble who independently measured the distance to Andromeda, forever changing our understanding of the Universe and our place in it. You can print out a star map to help you locate Andromeda on the sky - we've shown its position relative to the moon as it will be on Saturday, 3rd December, at 8pm.

So what does the future hold for Andromeda? Well, it certainly isn’t a boring one: Andromeda is expected to collide with the Milky Way in approximately 4.5 billion years! Using both ground and space based telescopes (like the Hubble Space Telescope) astronomers have taken stunning pictures of what happens when galaxies collide. From this, we know that our collision with Andromeda will be violent, with stars being flung out into deep space never to be seen again. However, mergers also stimulate the formation of new stars and planets, and so possibly life. Andromeda is the only galaxy that we can see with the naked eye (although a very dark night is needed). However, if the earth is still supporting life in 4.5 billion years time then our descendants night sky will be dominated by Andromeda and its hundreds of billions of stars!

This photo of Andromeda (otherwise known as M31) was taken with a small telescope by Robert Gendler, and was featured on NASA’s Astronomy Picture of the Day. You can see how Andromeda has spiral arms much like the Milky Way’s. The dark wisps are dust lanes which block background optical star light. The two fussy blobs directly above and below Andromeda are its dwarf satellite galaxies, M32 and M110 respectively.

Don’t forget that if you want to know about other objects up in the night sky this week, visit the Blackett Observatory’s What’s Up page.

Categories: what's up | night sky | galaxies | andromeda | stargazing