ANDROMEDA pronounced an-DROM-eh-dah.

The constellation Andromeda represents the daughter of Queen Cassiopeia and King Cepheus, who was chained to a rock as a sacrifice to the sea monster Cetus, until saved by the hero Perseus, whom she subsequently married.

This large northern constellation was recognised by the Greek astronomer Ptolemy in 150 AD. The unaided eye only sees an irregular line of the four brightest stars extending north-east (right and down) from the great square of Pegasus. Alpheratz (α Andromedae) forms one corner of the great square. This star, which is also known as Sirrah, marks the head of the chained Andromeda; another star in the line, Mirach, represents her waist, and a third, Almach, is her chained foot.

The most celebrated object in the constellation is the Andromeda Galaxy M 31, a spiral galaxy like our Milky Way, but larger, recognised as the most distant object visible to the unaided eye. Two stars leading from Mirach act as a guide to finding it. It is low down in the northern sky in New Zealand, and virtually impossible to see from the lower part of the South Island.

Chart showing Triangulum, Pegasus, and Andromeda in mid November.

To find Andromeda look north in the late evening sky and find the Great Square of Pegasus. The lower right corner of the Great Square is Alpheratz. The diagram is the view from Wellington. Aucklanders will see more of Andromeda, but conversely, South Islanders will see less.

Triangulum, Pegasus, and Andromeda

Some stars and interesting objects in the Constellation.

α Andromedae (Alpheratz or Sirrah) is a magnitude 2.1 blue-white star 97.1 light years away.

β And (Mirach) is a magnitude 2.1 red giant star 199 light years away.

γ And (Almak or Almach), is an outstanding triple star 355 light years away. Its two brightest components (mags. 2.2 and 5.0) form one of the finest pairs elegantly seen on small telescopes, with colours of orange-yellow and pale blue (by contrast). The fainter blue star has close 6th mag. blue companion. Unfortunately it is very close to the horizon for New Zealand observers.

M 31 (NGC 224) the celebrated Andromeda Galaxy is visible to the unaided eye from a dark sky site in the northern hemisphere. It was recorded in the 10th century by the Persian astronomer Al Sufi. It is an immense spiral galaxy, similar to the Milky Way in size and general composition. Binoculars or low magnification in a telescope help show the brightest central portion of this famous galaxy from northern parts of New Zealand. If the entire Andromeda Galaxy were bright enough to be seen by the unaided eye, it would appear five or six times the diameter of the full Moon. M 31 is accompanied by two small satellite galaxies, M 32 (NGC 221) and NGC 205, the equivalent of our Magellanic Clouds.

Visibility

Being a northerly constellation, Andromeda is, at best, only visible for a few hours each night. From the South Island, the most northerly parts of the constellation do not rise above the horizon.

Alpheratz, α And, is about 24° above the horizon at its highest as seen from Auckland. From the extreme south of New Zealand its maximum height is 14°. Most of the rest of the constellation is lower.

In terms of time the galaxy is above the horizon for about 6 hours 40 minutes as seen from Auckland, 5 hours 30 minutes from Wellington and 4 hours 40 minutes from Christchurch. Thus there is only a fairly brief window of opportunity to see the galaxy during the night. For New Zealand, it is due north, and highest, at about 10:30 pm (NZDT) in mid November, an hour later at the beginning of the month and an hour earlier by the end of the month. By the latter date it will be running into evening twilight. For each month before November, the galaxy will be at its highest two hours later. This means it is visible from New Zealand during the hours of darkness from about the beginning of July to the end of November.