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Facts About Spiral Galaxies

A spiral galaxy is a star system bound by gravity that resembles a pinwheel, best described as a disc with a bulging center that possesses brighter arms wheeling out from it in a spiral pattern.

Milky Way
- The galaxy our solar system exists within is the Milky Way galaxy, an example of a spiral galaxy.
Size
- According to the Sloan Digital Sky Survey website, over three-quarters of the galaxies that man has observed--some 77 percent--are spiral galaxies.
Rotation
- The NASA website states that all spiral galaxies rotate, with some taking eons to make one single rotation. For example, it takes the Milky Way 250 million years to complete one rotation.
Angles
- An edge-on spiral galaxy has a bright central bulging area.
  
  A spiral galaxy that has an angle that allows an observer from Earth to see the spiral shape with little difficulty is a "face-on" spiral. Those that someone can only view from the side, obscuring the fact that it is a spiral galaxy, are "edge-on" spirals; their bright middle bulge gives away that they are a spiral galaxy.
Types
- A tightly wrapped "type a" spiral
  
  How tightly wound the "arms" of a spiral galaxy appear help astronomers to classify further these groups of stars. A "type a" spiral has extremely tightly wound arms, a "type b" has less tightly wound spirals and the "type c" galaxy has very loose spirals.
Features
- Within the typical spiral galaxy, many new stars come into existence and there are large amounts of gases and dust. Globular clusters, smaller star formations that usually have as many as 100,000 stars in them, frequently encircle spiral galaxies.

Astronomy