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Additional Information

1. In the late 1920's, after examining the photographs of the structural appearance

2. of galaxies, Edwin P. Hubble, the American astronomer, classified the galaxies

3. into three distinct groups. These galaxies are comprised of stars that have

4. diverse structure, unequal degree of brightness, and definitely varied sizes.

5. One group, spirals, is highly luminous and has either a normal or a barred

6. structure. Normal spirals have two arms which radiate from the center of the

7. galaxy to the exterior edges. The two contrasting arms are enclosed in a disk

8. structure made up of stars; however, in the barred structure the arms radiate

9. from the top and the bottom of a bright bar that goes through the nucleus of the

10. galaxy. Barred spirals account for nearly 25 percent of all spirals. Over two-

11. thirds of eminent, highly luminous galaxies are Spirals. The Milky Way and

12. The Andromeda are examples of spiral galaxies. Another group referred to as

13. elliptical galaxies exhibits soft, but dim brightness and has two subgroups: The

14. giant and the dwarf. While the giant elliptical galaxies have countless large

15. luminous stars, the dwarf ellipticals have a smaller number of less luminous

16. stars. Together they make up less than one-third of the galaxies. The last group

17. is the irregularly-shaped galaxies, which are non-symmetric, and their pattern is

18. rather chaotic. They account for about 3% of the galaxies and their luminosity is

19. quite grainy. The Magellanic Cloud is an example of an irregularly-shaped galaxy.

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