NORTHERN CIRCUMPOLAR STARS
from Latitude 50 Degrees North.
By far the most well known star pattern in the Northern heavens is "The Plow, or Big Bear" in the constellation
of Ursa Major. The familiar seven stars which form the Plow are of significant importance to the amateur astronomer
as they can be used as direction finders to locate many other constellations and more important so, the Pole star,
called Polaris which is located in Ursa Minor, often called the Little Bear.
It would be easy to locate the Pole star if we were at the Earths North pole at latitude 90 degrees North. We could
look straight up and above us at the Zenith point where we would immediately see the 2nd magnitude star Polaris.
Polaris appears to remain quite stationary in the sky and will do so for many centuries to come. It will also be
noticed over a period of many hours that all the stars away from this star appear to form huge circles in an anti-
clockwise East West direction. This is due to our Earths West to East daily rotation.
To find Polaris from latitude 50 degrees North on the Earths surface is just as easy. Locate the two end stars
of the Plow, or Big Bear in Ursa Major. The two at the opposite end to the tail or handle of the familiar seven
star pattern. These two stars are named rightly so "The Pointers" and are " Alpha "Dubhe"
and Beta "Merak". Take a line from these until you arrive at the next bright naked eye star. This is
Polaris. It will be noticed that at this latitude its position will remain at all times at 50 degrees altitude
above the Northern horizon. When observed through a telescope of 3 inch diameter or larger with a moderate magnification
you will notice that it has a faint companion star of 9th magnitude. The angular separation of the two is 18 seconds
of arc. Also using very low magnifications or binoculars the little circlet of magnitude 7 to 8 stars meeting the
brighter Polaris named "The Diamond Ring" can be viewed. See Link on Homepage.
Now it will be quite apparent that stars with a greater Southern Declination than 50 degrees North will at some
stage or another throughout the year dip below the Northern horizon. However the stars that hug the Pole star within
the 50 degree circle will never ever set from this Latitude on Earth. These are the circumpolar stars. Having located
Polaris using the Pointers carry on in a relatively straight line and one will arrive at the M or the W shaped
constellation called Cassiopeia.
With Polaris sat at the centre like the hub of a giant wheel Ursa Major and Cassiopeia located at opposite sides
at any one time of the night can be seen to turn anti clockwise a full 360 degrees throughout the period of one
year taking on a different position in the sky. Hence when Ursa Major sits low down at the North horizon in Early
Winter Cassiopeia takes on the "M" high above at the Zenith.
In the constellation of Ursa Major one can view numerous deep sky objects. The four most viewed objects are Messier
81 (NGC 3031) an Sb type edge on spiral which in recent times boasted the supernova named 1993J of which many amateur
astronomers had occasion to observe and photograph. A supernova is a giant star ( type two) that has ended its
life in such a violent explosion that it can often outshine the parent galaxy system. A type one supernova is the
death of a companion white dwarf star in a binary star system that ends its life in a catastrophic split second
detonation. Close to Messier 81 lies the unusual elongated galaxy Messier 82 (NGC3034). A 4 inch telescope is necessary
to show them clearly as hazy patches of light. Move round the shape of the seven stars in the Plow from Dubhe and
Merak and take a straight line onto the third naked eye star Gamma. About a quarter of the way along one will arrive
at the planetary nebula Messier 97 (NGC 3556) called "The Owl nebula". This object requires at least
a 6 inch reflector and a low magnification. Much larger instruments are needed to reveal the two dark patches which
resemble eyes, hence its name. However deep sky astrophotographers are able to record the features using relatively
small apertures. Close to Messier 97 lies the illusive nearly edge on magnitude 10.8 galaxy Messier 108 (NGC3556)
which can be seen well in an 8.5 inch reflector. A good clear Monocles night however like so many deep sky objects
is required to see these two objects well. Now onto the last but one star of the tail of the Plow,or Big Bear and
one will view one of the most interesting of double stars in the heavens named "Mizar. Mizar has a companion
called "Alcor" which is of 4th magnitude. See photograph. I often use this star as a guide to determine
how transparent the sky is prior to an astrophotography session. If difficult to view with the naked eye clearly,
with the exception of when Ursa Major sits on the Northern horizon in Early Winter and is hampered by light pollution
and low altitude haze, I don't consider astrophotography as sky fog levels would render exposures of many minutes
or longer useless. Mizar itself is double star system consisting of 4th and 2.4 magnitude components. They have
an angular separation of 14.4 seconds of arc. A moderate magnification is needed in a small telescope to separate
them.
Now about Cassiopeia. The whole region is particularly rich in stars and nebulous regions and many fine classes
of objects can be found using small telescopes. Open star cluster NGC 581 known as Messier 103 is a fan shaped
cluster whereby open star clusters NGC 7654 known as Messier 52 is somewhat triangular in shape. Close to and below
the middle of the "W" is the open cluster NGC 457 which is very rich in stars and one of the brightest
in the sky. To sweep the skies with a good pair of small binoculars in this area will give much pleasure as stars
will be seen in their millions. next to Cassiopeia lies the Northern portion of the constellation of Perseus and
within this Northern portion in line with Cassiopeia lies the famous double cluster NGC 869 and NGC 884 These are
also called H and X Perseus. The double misty condensations can be glimpsed with the naked eye but through an 8
inch telescope stand out in magnificence.
On round the circumpolar skies and one will arrive at the constellation of Camelopardalis. One leaves the richness
of the Milky Way when entering this constellation but it may be worthy to observe the long period variable star
"S Cam" at position (2000) 05hrs41mins +68deg47min. It has a period of around 326 days. This is a star
that has been known to brighten to 8th magnitude, some three complete magnitudes brighter than its normal intensity.
The visual observers popularity in using the standard 6 inch reflector is armed with an ideal size of telescope
for this type of observation. I am sure that most societies variable star sections would be pleased to receive
any of your observations. Of the galaxies in this region IC 342 at position (2000) 03hrs46min49sec + 68deg05min
is one of my favourites for supernova hunting. In extremely good sky conditions the 12th magnitude central hub
surrounded by a very faint nebulosity can be observed using an 8 inch telescope. On astrophotographs the spiral
arms spread out into fine dusty spiral arms and are revealed in their full glory.
From Camelopardalis we pass through the Northern tip of the Constellation of Lynx and on into Ursa Major and the
seven stars of The Big Dipper. North of these lies the long trailing constellation of Draco which takes a path
from between The Pointers and Polaris right round the smaller constellation of Ursa Minor to a Declination a little
North of 70 degrees. From this point the stars of Draco head Southwards and ends just North of the non circumpolar
constellation of Hercules in the formation of a conspicuous asterism. At the head of Ursa Minor is a faint rectangle
of stars of which two namely Gamma and Beta are nicknamed "The Guards". Take a line from The guards and
arrive at Mizar in the Plow. Midway along the line is the star Alpha Draconis also known as Thuban. It is interesting
to note that Thuban was the Pole star back in 3500BC. Polaris at present is positioned just under 1 degree from
the true pole in the sky and will arrive at its closest true polar position in the year 2002AD. Even then it will
lie at about 27.5 minutes of arc distance.
From Draco we move onto the constellation of Cepheus with the Northern tip of Lacerta just in the circumpolar region.
Here we move into a more interesting area as the main plain of the Milky Way stars run through it. In Cepheus one
cannot go on without locating the beautiful red variable star Mu Cephei named "The Garnet star" by William
Herschel an English astronomer who discovered the planet Uranus. Positioned at 21hr43min +58deg46min (2000) The
Garnet Star is amongst the reddest stars to be seen with the naked eye. It is a variable star of a somewhat irregular
nature. Its magnitude ranges from 3.7 to 5.0 magnitude. Another object of interest is the open cluster NGC188 which
lies only about 4 degrees from Polaris. The cluster containing some 150 stars can be detected in an 8 inch telescope
but larger apertures are needed to detect all but a luminous patch and a few of the brighter members as most of
the stars are fainter than 13th magnitude. The galaxy NGC 6946 a large face on Sc type spiral galaxy lies only
38 minutes away from the open star cluster NGC 6939. These can be viewed in the same field using a low power. However
the 11th magnitude galaxy nucleus and a little surrounding nebulosity is all that can be viewed in average amateur
telescope.
I am sure that you will find a great deal more deep sky objects within the circumpolar skies and I trust that it
will spur you all on to observe These Constellations That Never Set.
NB:
The Volume 1 Uranometria 2000 star atlas is highly recommended to all who wish to discover for themselves the wonders
of the night sky.
Clear Skies and good star hunting.
By John R Fletcher. Mount Tuffley Observatory. UK