Milky Way

 

The Milky Way (a translation of the Latin Via Lacteal, in turn derived from the Greek Γαλαξίας (Galaxias) sometimes referred to simply as "the Galaxy"), 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, its special significance to humanity is that it is the home galaxy of our 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. 

Composition and structure

  The Galaxy consists of a bar-shaped core region surrounded by a disk of gas, dust and stars forming four distinct arm structures spiralling outward in algorithmic spiral shape . The mass distribution within the Galaxy closely resembles the Sbc Hubbell classification, which is a spiral galaxy with relatively loosely-wound arms. Astronomers first began to suspect that the Milky Way is a barred spiral galaxy in the 1990 slather than an ordinary spiral galaxy. Their suspicions were confirmed by the Spritzer Space Telescope observations in 2005 .which showed the Galaxy's central bar to be larger than previously suspected. The Milky Way's mass is thought to be about 5.8×10¹¹ solar masses (M_☉) comprising 200 to 400 billion stars. Its integrated absolute visual magnitude has been estimated to be −20.9. Most of the mass of the Galaxy is thought to be dark matter, forming a dark matter halo of an estimated 600–3000 billion M_☉ which is spread out relatively uniformly.