AUTUMN (NORTHERN HEMISPHERE)
It is often said that from the northern hemisphere the autumn stars are
the least interesting of the year. We have seen the best of the Summer
Triangle, and Orion has yet to make its entrance, but there is still plenty to
see. Vega is still high up, which means that Capella is low down. The main
autumn constellations are Pegasus and Andromeda, the constellation
which contains the magnificent Andromeda spiral galaxy.1easily seen with binoculars or a small telescope. Look and see how many
stars you can observe inside the square. From a city, you may seen none at
all. Anywhere between four and 12 is good, while above 12 means you have
excellent skies.The First Extrasolar Planet
Before leaving Pegasus, between the top right hand star, the orange Scheat
and the lower right hand star, Markab, not far away from the middle of a line
joining these two, is the inconspicuous star 51 Pegasi, which was the first
star found to be attended by a planet.
This discovery, made only in the 1990s, altered our thinking and
we now know of hundreds of extrasolar planets, but most have been
discovered indirectly and only in a few certain cases has the planet
actually been seen.In mythology Pegasus was a flying horse, and in the sky its main stars make
up a square which is easy to locate, although maps always make it look
smaller and brighter than it really is. For some reason the top left hand star
of the square, Alpheratz, which is obviously part of the Pegasus pattern,
was given a free transfer to the adjacent constellation of Andromeda by the
International Astronomical Union. What was Delta Pegasi, is now known as
Alpha Andromedae.
The stars of the square are not alike. Three of them, Alpheratz, Gamma
Pegasi (Algenib) and Alpha Pegasi (Markab), are bluish white. The top
right-hand star Beta Pegasi (Scheat) is obviously orange and is a semi-
regular variable ranging between magnitudes 2¼ and 2¾. This means
it is sometimes brighter than Markab and sometimes fainter with an
approximate period of 39 days. Outside the square to the west is Epsilon
Pegasi, Enif, and near here there is the fine globular cluster, M15, which is[1] Mira is a double star. Mira A is
the bright red variable giant star
at right, and its companion star a
small hot white dwarf is at left.[2] M31, the Andromeda galaxy,
photographed by Ian Sharp.[3] The sky in Autumn, with the
Square of Pegasus.2Astronomer Book