Galaxies are large systems of stars and interstellar matter, typically containing several million to 
some trillion stars.  Some masses are between several million and several trillion times that of 
our Sun.  Some galaxies contain extensions of a few thousand to several hundred thousand light 
years, typically separated by millions of light years.  They come in a variety of flavors: Spiral, 
lenticular, elliptical and irregular. Besides simple stars, they typically contain various types of star 
clusters and nebulae.

We live in a giant spiral galaxy, the Milky Way Galaxy, that measures 100,000 light years in 
diameter, and has a mass of roughly a trillion solar masses. The nearest dwarf galaxies, satellites 
of the Milky Way, are only a few 100,000 light years distant, while the nearest giant neighbor, the 
Andromeda Galaxy, also a spiral, is about 2-3 million light years distant.

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