Astronomer Book
By city of the stars we mean our own particular Galaxy, the
Milky Way, though technically the Milky Way is the main plane
of our Galaxy where a great many stars lie in roughly the
same direction. When we look up into the night sky with the
naked eye we see the 88 star patterns, or constellations, that
fill the sky. The constellations were originally maps made by
astronomers in ancient times.CITY OF THE STARS
night sky lie within our own galaxy in a "bubble" of visibility which is
approximately 10,000 light years in diameter. There are many other stars- several hundred billion in total in the Milky Way Galaxy alone – lying
outside of this bubble which are too far to be seen individually with the
naked eye. The light from these distant suns merges together to form the
misty path that we sometimes see running across a dark moonless night.
It is amazing to reflect that some people who live in city centres have
never seen the Milky Way at all. Not long ago a party of school children
from inner London came to Patrick Moore’s observatory and when shown
the Milky Way crossing the sky they were incredulous. Light pollution is
a serious problem and although some councils are doing their best to
limit the damage it is fair to say there are not many areas left into which
artificial lights do not intrude in some way or other.
There are many different types of stars in our galaxy, including so
called main sequence stars like our Sun, huge red giants, supergiants and
hypergiants. At the other end of the scale there are stars which are much
smaller than our own Sun, such as white dwarfs, red dwarfs and exotic
objects such as neutron stars. There is a tremendous range in luminosity
too and with the naked eye one can see stars which are many thousands
of times brighter than our own Sun which appear like dim twinkling
points simply because they are very distant indeed.
Once we go beyond the Solar System, our own particular part of the
Universe, we have to deal with distance of quite a different order. This is
where we use light years rather than miles or kilometres which are far
too short. An important point here is that no one can really understand
these huge distances. Can you picture a million miles, let alone 24 million
million – the distance to the next nearest star to the Sun? We certainly
cannot and it’s virtually impossible to put these distances meaningfully
into plain language.
The distance to the nearest star, Proxima Centauri, becomes
somewhat trivial as you head out into the deepest depths of space. At
4.2 light years distant Proxima is a near neighbour in the gravitationally
bound island city of stars that we call our Galaxy. Measuring
approximately 100,000 light years in diameter, the best model for the
Milky Way is to think of two fried eggs slapped back to back. The bulge in
the middle represents the core of the galaxy, while the flatter whites are
where the spiral arms are located – vast regions of star birth. The stars in
the arms are younger than those at the core so from a distance, the core
of a spiral galaxy such as ours appears redder than the hot blue stars
which give the spiral arms their form.
Our Sun lies approximately two-thirds of the way from the core
towards the edge of the galaxy. All of the individual stars we see in the[1] The star Sirius (the "Dog Star")
is the brightest night time star in the
entire sky. It lies in the constellation of
Canis Major, the Great Dog.
[2] Planetary nebulae, seen by the
Hubble Space Telescope. NASA.
[3] Sirius is the brightest star in the
sky in this photograph taken from the
Canary Islands by Nik Szymanek.
[4] The Dumbbell Nebula (Messier
27) is located in the constellation of
Vulpecula, the Fox. (RGB filtered mono-
CCD camera image).1