The main types of galaxies are Spiral galaxies, Elliptical galaxies, Lenticular galaxies, and Irregular galaxies.

• Spiral (and Barred-Spiral) galaxies are shaped like pinwheels, with arms that spiral outward. The barred spiral has an elongated bar shape across the middle. Examples of the spiral are our own Milky Way and Andromeda. A barred spiral is the Sculptor Galaxy.
• Elliptical galaxies look like flattened spheres rather than the thinner spiral form. They are observed to have comparatively little interstellar matter. An example is the Maffei 1 galaxy.
• Lenticular galaxies are flattened galaxies without an obvious spiral structure. An example is the Spindle Galaxy in Draco.
• Irregular galaxies do not have any of the common shapes, and may have been disrupted by various forces. These include Hoag's Galaxy (a ring), the Magellanic Clouds, and NGC 1427A (which is speeding toward the Fornax cluster).

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The strongest consensus (nearunanimous of the astronomical community is that the redshifts of distant galaxies indicate that all distant galaxies arerecedingfrom us. This recession is currently the only known mechanism for redshifting light. Take this inference, that all galaxies arereceding and you are led to the idea that the universe is expanding, a phenomena described by Hubble's Law. This is a central tenet to the Big Bang Theory.

I will include the counterpoint originally described below, but I will point out that the papers cited are very old, and a huge number of corroborating observations and predictions of the big bang haveoccurredsince then.


The conclusion that the Universe is expanding is a wrong conclusion. Alan Sandage talks about Hubble's position at the related link below.

To the very end of his writings he maintained this position, favouring (or at the very least keeping open) the model where no true expansion exists, and therefore that the redshift "represents a hitherto unrecognized principle of nature". This viewpoint is emphasized (a) in The Realm of the Nebulae, (b) in his reply (Hubble 1937a) to the criticisms of the 1936 papers by Eddington and by McVittie, and (c) in his 1937 Rhodes Lectures published as The Observational Approach to Cosmology (Hubble 1937b). It also persists in his last published scientific paper which is an account of his Darwin Lecture (Hubble 1953).

• Milky Way Galaxy - Our Galaxy
• Omega Centauri - former galaxy - 0.0183 million light years away
• Canis Major Dwarf - 0.025 million light years away
• Virgo Stellar Stream - 0.03 million light years away
• Sagittarius Dwarf Elliptical Galaxy - 0.81 million light years away
• Large Magellanic Cloud - 0.163 million light years away
• Andromeda Galaxy - Largest - 2.5 million miles away.

The Canis Major Dwarf Galaxy orbits the Milky Way at 42,000 light years from the galactic center. The Sagittarius Dwarf Elliptical Galaxy orbits at 50,000 light years. The Large and Small Magellanic Clouds are also very close to the Milky Way, but there is some debate over whether they are "orbiting" the larger galaxy. However, orbiting or not, they are still considered "satellites" of the Milky Way. All of these galaxies are very small compared to the Milky Way and most are irregular in shape, all of them lacking the spiral structure normally associated with a well-organized galaxy. The Phoenix Dwarf Galaxy is 1.44 million light years from the center of the Milky Way, and NGC 6822 (aka Barnard's Galaxy) is 1.6 million light years away.

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A galaxy is a vast, gravitationally bound collection of billions of stars and their associated "friends."

Their "friends" include nebulae, stellar remnants, planets and a whole host of other smaller particles including the basic elements hydrogen and helium. Galaxies also consist of an important but poorly understood substance called dark matter. It is believed to surround every galaxy and accounts for much of its mass.

Galaxies vary in size and shape. They range from dwarfs that may only consist of a few million stars to giants that can have trillions of them, all orbiting a center of mass. Galaxies are categorized based on their apparent shapes. Elliptical galaxies are bright, featureless spheroids consisting mostly of old, low-mass stars. Spiral galaxies are disk shaped and have a variety of stars, and irregular galaxies are a catch-all for those with no distinct shape.

Many galaxies, including the Milky Way, orbit around what is to believed to be a supermassive black hole--smaller than a pinhead but with the mass of millions or billions of Suns. The supermassive black hole in the center of our galaxy flattens it into a disk with a depth of a few light years, whereas the diameter is about 100,000 light years.

It is estimated that there are between 100-300 billiongalaxies in the observable Universe!

1. A galaxy is system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

The figure of 200 to 400 billion is considered to be

today's most reliable estimate. (late 2012)

(Minor Comment: It's not clear if this question refers to the whole Milky Way Galaxy or to just the band of stars called the Milky Way.)