As far as you can see

Time lapse photography captures M31’s transit above the Southern Alps. IMAGE: IAN GRIFFIN
Time lapse photography captures M31’s transit above the Southern Alps. IMAGE: IAN GRIFFIN
Next weekend I will be at the University of Canterbury’s Mount John Observatory. With the new moon occurring on Friday morning I will be hoping to enjoy some wonderful views of the heavens in a sky devoid of moonlight, writes Ian Griffin.

Ian Griffin
Ian Griffin
One object I am particularly looking forward to seeing is the Great Andromeda galaxy. Astronomers call this object Messier 31 (M31) because it was the 31st object catalogued by Charles Messier, a prominent 18th-century French comet hunter. M31 rises just after 9pm and reaches its highest point in the sky, just a few degrees above the northern horizon, at about 11.30pm.

Normally, I wouldn’t encourage you to look for objects that are low in the sky. That is because, even when the sky is clear, their light is attenuated by thick layers of our atmosphere.

However, the Andromeda galaxy is definitely worth making the effort to spot in order to gain some pretty cool bragging rights. You can tell your friends you have seen the most distant object humans can see without a telescope.

M31 is a very long way away. Astronomers calculate that the distance to this object is 2.5 million light-years. The light you see when looking at this dim celestial smudge - travelling at a speed of 300,000km every second - began its journey at a time before hominids knew how to make fire!

To observe M31, you will need to find a location with an unobscured northern horizon. As noted earlier, the galaxy is highest in the sky at 11.30pm which is the best time to try to find it. Look for a really dim fuzzy smudge a few degrees above the horizon.

From Dunedin, the galaxy’s peak altitude is just three degrees, while from Tekapo it will appear a little higher. This week’s accompanying photograph shows M31 above the Southern Alps as seen from Mount John in September 2020.

Astronomers tell us that M31 is on course to collide with our own Milky Way galaxy in about six billion years time. The views of this object are going to get better and better!


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