In Greek mythology Andromeda was the princess that was chained to a rock as a sacrifice to the sea monster Cetus. Andromeda is also the name of an ancient constellation that contains the most distant object that can be seen with the unaided eye.
Our Sun is a star in the Milky Way Galaxy. We can only see a small fraction of this galaxy because we are embedded within it… We can’t see the forest for the trees. It is over 100,000 light-years in diameter and contains at least 150,000 million stars. Late on a spring evening the Milky Way lays along the Southern horizon. The Southern Cross, which is embedded in the Milky Way, reaches its lowest point in the sky and grazes the southern horizon.
Looking to the north, away from the Milky Way, we have a window into the greater universe. The most prominent feature is a group of four stars that form the ‘Great Square’. Below and a little to the right of the Square, close to the horizon, is the constellation of Andromeda. On a clear dark night you may glimpse a small faint elliptical patch of light. This is M31, the Great Galaxy in Andromeda. With a distance of 2,537,000 light-years it is the most distant object that you can see without optical aid. It is similar to, but slightly larger than our Milky Way galaxy. It has a diameter of 152,000 light-years and contains a trillion stars.
The Andromeda galaxy is on a collision course with the Milky Way. It is approaching us at the rate of 110 kilometers per second. However, don’t panic. Although its approach is much faster than a speeding bullet, the distance is so great that the collision is not due for another 4 billion years.
Richard Hall
Stonehenge Aotearoa
Photo credit – Messier 31, Andromeda Spiral Galaxy, Boris Štromar