Milky Way Galaxy

Type                               SBbc (barred spiral galaxy)

Diameter                           100,000 light years

Thickness                          1,000 light years (stars)

Number of stars                    200 to 400 billion

Oldest star                        13.2 billion years

Mass                               5.8×1011 M

Sun's distance to galactic center  26,000 ± 1400 light-years

Sun's galactic rotation period     220 million years (negative rotation)

Spiral pattern rotation period     50 million years

Bar pattern rotation period        15 to 18 million years

The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. Although the Milky Way is one of billions of galaxies in the observable universe, the Galaxy has special significance to humanity as it is the home galaxy of the Solar System. The plane of the Milky Way galaxy is visible from Earth as a band of light in the night sky, and it is the appearance of this band of light which has inspired the name for our galaxy.

Some sources hold that, strictly speaking, the term Milky Way should refer exclusively to the observation of the band of light, while the full name Milky Way Galaxy, or alternatively the Galaxy should be used to describe our galaxy as an astrophysical whole. It is unclear how widespread the usage of this convention is, however, and the term Milky Way is routinely used in either context.