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Milky Way 
Spiral galaxy composed of 200 to 300 billion stars, including the Sun; thought to be 10 billion years old.
Milky Way (seen from above)
From above, the Milky Way appears as a spiral that rotates on itself around a nucleus.
nucleus
Central region of the bulge; the densest and most luminous region.
spiral arm
Curved grouping of stars influenced by the rotation of the galaxy around its nucleus.
Milky Way (side view)
From the side, the Milky Way appears as a disk because its spiral arms are seen from the same angle.
halo
Region surrounding the galaxy, inhabited by isolated stars or groupings called globular clusters; the halo has a radius of about 50,000 light-years.
disk
The main part of the galaxy, made up of a bulge and attaching arms.
bulge
The central bulge of the Milky Way’s disk; the densest region of the Milky Way, with a depth of 15,000 light-years.
globular cluster
Cluster made up of hundreds of thousands of old stars.
