Star Atlas
Downwards (south), Scheat and Markab point to Fomalhaut in the
Southern Fish, the southernmost of the first magnitude stars visible from
Britain. It is 22 light years away and 13 times as luminous as our Sun. We
already know it is a planetary centre, and one planet, Fomalhaut B, has
been imaged.
Mira
A line drawn from Scheat in the upper right of the square, through
Algenib in the lower left, extended for two times the distance again, will
land you in the constellation of Cetus, the Whale or Sea Monster. The
most famous object here is the variable star Mira. It has a period of 332
days and ranges from magnitudes two to nine. At its best it is prominent
to the naked eye and is clearly red. On average it remains visible only
for a few weeks in the year. Like all stars of its type the maximum
magnitude is never really predictable and there are times when the star
never rises above magnitude three. Patrick Moore had seen it reach the
first magnitude for a few nights. This was the first variable of its type to
be identified. We now know that Mira variables are very common indeed.
Most are a long way away and very few reach naked-eye visibility.
The Andromeda Galaxy
Come back to Andromeda, and we see a line of stars extending away
from Alpheratz, of which two are of special interest. Almaak (Gamma
Andromedae) is a lovely double star, while the orange Mirak (Beta
Andromedae) is a guide to M31 – the great spiral galaxy in Andromeda, the
nearest large external galaxy. It is easily visible with the naked eye when you
know where to look, but in a small telescope it tends to be a disappointment,
because it lies at an unfavourable angle to us and its outer regions are
surprisingly faint. What we see with the naked eye or binoculars is just
the bright core of M31. This was the first galaxy shown to be an external
system rather than part of the Milky Way. The discovery was made by Edwin
Hubble over 80 years ago. He found Cepheid variables using the Mount
Wilson 100-inch telescope, inside galaxies, and these useful stars give
away their distances by their behaviour. This is probably the most important
astronomical discovery of modern time. It showed our Galaxy is only one of
many and is not even exceptional; it may be somewhat smaller than M31.
The Andromeda spiral has two satellite galaxies M32 and M110, easily
seen with binoculars. The whole group is a favourite target for many
astronomical photographers.Autumn Meteors
There are several autumn meteor showers. The Draconids peak on 10
October, are usually weak but do display occasional storms. They are
associated with the periodical comet Giacobini Zinner. The Orionids,
lasting from 16-27 October are associated with Halley’s Comet and are
characterised by swift meteors leaving fine trails.3