The diameters of these clusters range from about 75 light years to as much as 400 light years and can be as far as 300,000 light years from the Earth.

In many parts of the Milky Way galaxy, there exist dense concentrations of interstellar matter known as nebula and are generally classified as emission nebula, reflection nebula or dark nebula. Emission nebula are by far the most exotic, for they contain one or more extremely hot and luminous type O or B. stars (i.e. gas giants). The ultraviolet light form the stars within this type of nebula "excites hydrogen and oxygen atoms which gives these nebulae their characteristic greenish-yellow and red glows." An excellent example is the Great Nebula in the constellation of Orion, "where very young, hot stars excite the gases left over from their formation" (Parker, 1988, 256).

Of course, all astronomers have pondered exactly when all of...
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