Welcome to the sixth of Fun Science‘s CosWatch blog posts, which you can read through with your young scientist and learn how to see Andromeda, our galactic next-door neighbour.

What is CosWatch?

There’s so much to see in the night sky! You may have seen Brian Cox on TV describing the “wonders of the universe”, or Carl Sagan talking about the “awesome machinery of nature”, and they’re absolutely right. But while huge rockets and observatories can help, space isn’t just for people with expensive equipment. You can see amazing things from millions of miles away from your very own back garden. Each week, I’m going to talk about one of these incredible objects, and how you can find them. Today we look for Andromeda, a place far distant from any of our other CosWatch blog focusses.
APOD provides us with this ethereal picture of Andromeda.

What is Andromeda?

We live in a galaxy – a collection of stars, usually in a disk shape – called the Milky Way. Andromeda is simply another such galaxy. Though perhaps the most well-known galaxy other than our own, the Andromeda galaxy isn’t technically the closest; this is because the Milky Way and Andromeda both have “satellite” galaxies, a bit like the moons of a planet. It is, however, the largest galaxy in a big nest of galaxies of which we are a member; this is called the “local group”. Andromeda is sometimes called “M31”. This means it is the 31st entry in something called the “Messier catalogue”. This is a list started by French Astronomer Charles Messier of fuzzy, difficult-to-identify objects in the night sky, including nebulae and star clusters. Andromeda’s satellites have similiar entries in the catalogue – M32, for instance.

The past and the future

Despite being larger, Andromeda is more like our galaxy’s little brother than older sister; it is ten billion years old, some three billion years younger than the Milky Way. It was formed from the collision of several protogalaxies, which you can think of as galaxy babies. Andromeda was first recorded as being observed by human beings in 964 AD. However, it and other spiral galaxies were thought to be nebulae into the 1900s. There was a great debate by two scientists as to whether these “spiral nebulae” were just nebulae or “island universes”. It was settled when Edwin Hubble observed a flashing star, which he was able to use to measure the distance to Andromeda. It became quickly apparent that this object was further away than anything else we had observed, and was probably another galaxy.
An article by Ella Alderson provides this demonstration of a galactic collision.
The Milky Way and Andromeda are heading towards each other at over 68 miles a second – incredibly fast from our perspective, but for objects as big as galaxies, really rather slow. In about 4.5 billion years – when Earth will be twice as old – they will collide and combine into one galaxy, dubbed “Milkdromeda”. This may result in the solar system being ejected from the galaxies. Don’t panic, though; humans as we know them will be long-gone, and any still-existing lifeforms will probably be alright, as Earth will still orbit the Sun.

Visiting Andromeda

Since it was discovered to be another galaxy, Andromeda has featured in many science fiction stories. It is the main setting for the game Mass Effect: Andromeda, as well as the film Guardians of the Galaxy. It’s also the setting of Andromeda, a series by Star Trek creator Gene Roddenberry.
The game map of Mass Effect: Andromeda. The various locations of this game are no match to the actual population of Andromeda, which is estimated to have something like a trillion stars!
Unfortunately, in real life, we probably can’t visit Andromeda. The laws of physics seem to say that we can only travel as fast as the speed of light; even if we did manage to match light with a probe or space ship, it would still take us 2.537 million years to reach the place. Fortunately, there’s plenty we can learn about it from simply observing it in the sky.

How can I see Andromeda?

The Andromeda galaxy is the only galaxy visible with the naked eye, albeit on moonless nights; despite being so far away, the brightness of its collected stars makes it very powerful. It forms part of the conveniently named Andromeda constellation. To find it in the night sky, you need to find the “Mirach” nearby; think of it like using a sign post to choose the right lane on the motorway.
This diagram from WikiHow eloquently demonstrates how to find Mirach (and thus Andromeda) between the Cassiopeia and Pegasus constellations.
Fortunately, Mirach doesn’t move erratically in the way the planets do (there’s a reason “planet” is Greek for “wanderer”), so you should always be able to find it in this spot. Just use a star chart (or website like timeanddate.com) to work out when those constellations will be visible in your area, and you’ll be set! There are some benefits to observing Andromeda with a telescope. You may be able to see some of Andromeda’s twenty dwarf satellite galaxies. The image below was taken in 1899; imagine what you could do from your own garden with a whole century of technology on top!

In conclusion:

  • Andromeda is another galaxy, bigger than the Milky Way but younger.
  • It is the largest galaxy in our galactic “local group”.
  • Sometimes people call it “M31” because it is part of a record of space things called the “Messier catalogue”.
  • It has been observed since the 900s but was only determined to be another galaxy in the 20th century.
  • It will collide with the Milky Way in several billion years.
  • We probably can’t visit it, but we can certainly learn lots about it from observation.
  • It can be seen with the naked eye near the Cassiopeia and Pegasus nebulae.
  • Telescopes can reveal smaller galaxies next to it.

What’s next on CosWatch?

Next time, we’ll look at Comet NEOWISE, a rare Astronomical opportunity this month. Don’t miss it!


Fun Science recently created a “Planets and Space” home kit, available now for only £5.00. Check it out here! If your young scientist is interested, they may like to hear about blue-shifting. Because Andromeda is heading towards us, its light waves are being compressed, which makes them bluer; if it was moving away, they would be being stretched, making it appear redder. It’s quite well-explained in this gif shared on the Fun Science Twitter page.

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