Andromeda is a constellation in the Northern sky. It is home to the Andromeda galaxy, which is the nearest comparably-sized galaxy to ours. The Andromeda galaxy is also called M31, Messier 31, or the Great Spiral Galaxy.
It is one of the most faraway objects in the night sky the naked human eye can see. It is much easier to see with a telescope or binoculars though.
The Andromeda galaxy is estimated to contain anywhere between a few thousand and a trillion stars. It is about 2.5 million light years away.
The first written evidence of its existence was noted by a Persian astronomer known as Abd al-Rahman al-Sufi in A.D. 964. He described it in his Book of Fixed Stars as “a small cloud”.
In 1612, not long after the telescope was invented, Simon Marius spotted Andromeda. He was a German astronomer and described it as “a candle flame seen through [a] transparent horn [lantern]”.
What are the best conditions to see Andromeda?
A clear night sky is the best time to see Andromeda. The best time of year to see it is in the autumn or winter months.
It is easier to spot in the Northern Hemisphere than the Southern. In the Northern Hemisphere, October to December is the best time. In the Southern Hemisphere it is August to September.
Try to stargaze away from light pollution. Where possible, try to get away from urban areas with lots of streetlights, like cities.
Try to look for it on a night without the moon - such as the new moon. A crescent moon will also make it easier to spot. You can work out what phase of the moon you are in by looking at a lunar calendar.
Try to look for Andromeda on a cloudless night. Clouds can obstruct your view of the stars.
You should allow some time for your eyes to adjust to the darkness of the night. Andromeda is one of the less bright galaxies and can be difficult to spot immediately. We recommend allowing 15 minutes without screens or artificial lights for your eyes to adapt.
How do you find Andromeda using Cassiopeia?
We recommend looking at a star chart to identify what Andromeda looks like.
Below is one we found on Space.com to indicate the rough shape and the stars involved.
If you are looking at a star chart, we suggest printing it out to get a better idea of the scale. If you choose to do this, we suggest buying a red flashlight to look at it. This will not ruin your dark perception
If these charts confuse you (don’t worry, they take time to learn to read) there are alternatives. There are many smartphone applications that can be used to help you find constellations.
These will use your location, the season, and the time of day to adjust the star charts. This helps you track and identify stars, galaxies, and constellations with ease.
Some of our favorite apps include Star Walk 2, SkyView Lite, and Sky Safari.
If you know what the Big Dipper constellation looks like, try to find this first. Look for a very bright star to one side of it. This is known as the North Star, or Polaris. Look to the right of this star for 5 more stars arranged in the shape of a W. This is the Cassiopeia constellation.
In the Northern Hemisphere, Cassiopeia is known as a circumpolar constellation. This means it can always be seen above the horizon.
Directly underneath the 3rd star in Cassiopeia, you should see the Andromeda constellation. If you are still struggling, look for a large rectangle to the right. This should have 2 lines of stars coming out of the top left corner. This is the Andromeda constellation.
Look at the smudge labeled M31 on the star chart below, from Universe Today. This is the Andromeda Galaxy. It is a blurry, oval shape.
Once you have found the constellation or galaxy with your naked eye, we suggest using a telescope set to the lowest magnification.
It will appear huge and a large magnification will mean you cannot see the entire thing at once.
How do you find Andromeda using the Great Square of Pegasus?
If you cannot find Cassiopeia, try looking for the Great Square of Pegasus, as shown below in a Skyledge star chart.
The Andromeda constellation begins at the top left corner of the Great Square from the star labeled Alpheratz. It appears as 2 lines of stars coming out of the corner.
The 2 images below show different labelings of the constellations. If you draw a line straight from Mirach to Mu Andromedae, you will hit the Andromeda galaxy.
How fast is Andromeda moving towards us?
According to Astronomy.com, we can figure this out by looking at what color the light is Doppler shifted towards. Objects moving towards us have light Doppler shifted towards the red end of the spectrum, and away from us it is shifted towards the blue end.
Using this information, we can work out Andromeda is moving towards the Milky Way at a speed of 68 miles a second (110 kilometers). The light from the galaxy is speeding at 186,000 miles (300,000 kilometers) a second.
The closer Andromeda becomes to the Milky Way, the stronger the gravitational attraction between the galaxies becomes. This forces the Andromeda galaxy to speed up towards us.
Estimates suggest Andromeda is on course to collide with the Milky Way in about 4 billion years time. This will likely be catastrophic to all life in both galaxies and the remnants will merge to form a new galaxy.
Is Andromeda larger than the Milky Way?
For a while, it was believed Andromeda is bigger than the Milky Way. In 2019, a European Space Agency report published a calculated mass of our galaxy.
This estimate is more accurate than any before and proves the Milky Way is larger than Andromeda.