Collection of
nebulae,
stars,
dust, and other
matter that is typically
tens or
hundreds of
thousands of
light years in
diameter.
Galaxies come in all sorts of different
shapes and
sizes. Our galaxy, which we call
the Milky Way is a
spiral galaxy, so named because, suprisingly enough, it looks somewhat like a spiral.
IIRC begin cluelessness , our galaxy has 3 spiral arms, each with a particular name - the spiral arm we are in is called the Saggitarius arm. (?)(sp?)
end cluelessness
Galaxies are typically described by their form. Some common types:
I used to know a lot more, but it has been years since I was an astronomy nut...sorry :)
Galaxies are organised into
groups and
superclusters of anywhere from a few to millions of galaxies. Our galaxy's group, the oh-so-originally named
Local Group, contains many galaxies, of which ours is the second largest. The largest galaxy in the
Local Group is the
Andromeda galaxy, which is visible to the naked eye on a good night.
Our galaxy has two smaller galaxies
orbiting it: the Small and Large Magellanic Clouds, or
LMC and
GMC for short. Galaxies are generally thought to have
black holes at the center; ours, apparently, is no
exception.
One more fact (?): apparently, the
arms of a spiral galaxy are not 'really' there. The illusion is caused by 'waves' of star formation which 'ripple' around the galaxy, propelled by
supernovae
triggering nearby
nebulae to
contract into new
stars.
Components of a galaxy do, however,
orbit the
center - just not at the same
speed as the
arms.