Milky Way's Spiral Arms Are the Product of an Intergalactic Collision Course; Models Show Dark Matter Packs a Punch
The Milky Way is a barred spiral galaxy which forms part of the Local Group.
Although the Milky Way is but one of billions of galaxies in the universe, the Galaxy has special significance to humanity as it is the home of the solar system.
The term "milky" originates from the hazy band of white light appearing across the celestial sphere visible from Earth, which comprises stars and other material lying within the galactic plane.
The galaxy appears brightest in the direction of Sagittarius, towards the galactic center.
Relative to the celestial equator, the Milky Way passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic relative to the galactic plane.
The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the solar system lies close to the galactic plane.
The main disk of the Milky Way Galaxy is about 80,000 to 100,000 light-years in diameter, about 250,000 to 300,000 light-years in circumference, and outside the Galactic core, about 1,000 light-years in thickness.
It is composed of 200 to 400 billion stars.
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