From Earth, we gaze out on the spectacular "city
of stars" that we call our Milky Way galaxy. Only the nearest
stars in our galaxy can be seen as individual points of light.
The rest are so distant and so numerous that they seem to form
a continuous band of light across the sky. Dark splotches hide
some of the light; these are immense regions of dust and gas
from which new stars are continually born.
Our galaxy is
huge: On the scale of the drawing at upper left, the whole solar
system -- Earth, Sun, and planets -- would be smaller than an