Download 3.1e Finding Polaris and Sirius

3.1e
demonstrate the use of ‘pointers’ and other techniques to find other celestial
objects, including:
i Arcturus and Polaris from the Plough
ii Sirius, Aldebaran and the Pleiades from Orion
iii Fomalhaut and the Andromeda Galaxy from the Great Square of Pegasus
i Arcturus and Polaris from the Plough
Pointers are used by astronomers to help guide people to new regions of the night
sky. There are a number of excellent imaginary lines that can guide a person in a
straight line to locate an important star. Finding Polaris, the Pole Star (to point
north) is an excellent example:-
Finding North, the Pole Star (Polaris) from the Plough
POLARIS - The Pole Star
(part of Ursa Minor)
DUBHE
THE PLOUGH
(part of Ursa Major)
MERAK
To find North, the two stars of the PLOUGH, Dubhe and Merak, are used as
‘pointers’. Following along the line from Merak through Dubhe across the sky will
bring you close to Polaris – the first bright star in the region. The North Star is not
directly on the line because PRECESSION means that Polaris will move away from
being the ‘North Star’ in the future.
Sometimes a straight line will not work and a smooth curve is used.
Arcturus from the Plough is a good example of this:-
Finding
Finding Arcturus, in the constellation Boötes, from the Plough
To Polaris
Boötes
Arcturus
Using the handle of the ‘Big Dipper’ or the ‘saucepan’ gives a
natural curve from the Plough. This brings you down to the
brightest star in the constellation of Boötes, which is the
magnitude -0.05 star Arcturus - the brightest star of the northern
hemisphere and the fourth brightest star in the night sky.
Many people are told of the technique to find north using the ‘pointer’ stars of the
Plough. The same two ‘pointer’ stars can be used to find another important area of
the night sky – particularly useful in spring and summer. If you use the stars as your
line, but this time move in the opposite direction (the same distance that was used
to reach the Pole Star), you come to the constellation of Leo.
ii Sirius, Aldebaran and the Pleiades from Orion
The Pleiades
(M45)
Aldebaran in the
constellation
Taurus, the Bull
Orion, the Hunter
Orion’s Belt
Sirius
To find Sirius, the Dog Star and the brightest star in the night sky, the three stars of
Orion’s Belt are used as ‘pointers’. Following along the line down from Orion’s Belt
across the sky will bring you to Sirius.
Using Orion’s Belt as ‘pointers’, but this time moving in the opposite direction, you
pass through part of the constellation of Taurus which is shaped like a letter V. The
brightest star of the V is Aldebaran – an orange giant star. Carrying further along
the line brings you to the bright Open Cluster (M45), the Pleiades.
iii Fomalhaut and the Andromeda Galaxy from the Great Square of Pegasus
Star hopping is used to find the Andromeda Galaxy (M31). If you live where you
have very dark skies, the Andromeda Galaxy is the furthest object that you can see
with your naked eye – 2.4 million light years away! The galaxy appears as a small,
white, fuzzy patch. When you have found the Great Square of Pegasus, you need to
find the top left hand star of the square (the star does not belong to the
constellation of Pegasus – it actually forms part of the Andromeda constellation).
There are two faint pairs of stars that appear in the order as shown below. If you
move past the first pair and concentrate on the second pair – moving from the
bottom star of the pair to the top star of the pair, move up the same sized gap again
in the same line and you are in the area of the Andromeda Galaxy. Using a pair of
binoculars will allow you to see the large galaxy easily.
Andromeda Galaxy (M 31)
Great Square
of Pegasus
Fomalhaut
(in the Southern Fish
constellation)
The star is at declination -30˚
and so the star will only be
seen easily in the summer
Using the two stars on the
right of the Great Square of
Pegasus - follow the line
down. The first bright star
that you meet is Fomalhaut.