Below is a picture of an all-sky view
from the ground, with the horizon forming the circle and part of the
Milky Way band stretching from lower left to upper right - note that
most of the stars are concentrated into a flat plane, and that dust
and gas clouds block out a lot of the stars in the plane and prevent
us from seeing very far through our galaxy.
Note: there is a bluish-colored comet to the middle-left side of
this all-sky view.
Closeup of a section of the Milky Way band showing the gas and dust clouds...
A composite view of the entire sky (both hemispheres) centered on the center of the Milky Way - it's easy to see that most of the stars are concentrated into a flat plane, and that dust and gas clouds block out a lot of the stars in the plane.
We can use pictures like these of our galaxy
to determine what it would look like if
we could view it from the outside. From these pictures, we can
tell that we live in a round, flat galaxy, full of dust and gas clouds
that block out the light from some of the stars. How do we know? Well,
think of standing in a crowd of people: when you look around into the crowd,
you see lots of people - in fact you see so many people that
eventually they totally block your view of what's beyond. But, If you
look above, or below, you see few or no people. This is exactly
the same thing that we see in our galaxy: as we look into the plane of
the disk, we are looking into the crowd of stars, but as we look above
and below the plane, we see only a few stars.
To find out more about what our galaxy looks like,
astronomers study other galaxies in the universe, and look for the same
characteristics in other galaxies that we see in our galaxy.
Next: Edge-on
Spiral Galaxies
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