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Stars and Magnitude

The stars are hot balls of glowing gas just like our own sun.  Most of the visible stars are much brighter than our sun, but because of there great distances they appear as pinpoints of light to us. The most apparent distinction of a star is its brightness. Although stars have color is hard to discern at first but in time you may see the subtle hues. Good color star atlases are available to help in this. The brightness of stars is express by it's magnitude. The ancient Greeks referred to the brightest stars as 'stars of the first magnitude', and then the next brightest as 'stars of the second magnitude'. The visible stars extend down to the 6th magnitude.

Notices how fainter stars will have larger numbers for their magnitudes. A star of magnitude 6 will be fainter than a star of magnitude 5. Stars of the 6th magnitude are just visible to the naked eye. These 6th magnitude stars are 100 times fainter than stars of the 1st magnitude. Each magnitude 2.512 times fainter than its preceding number. A difference of five magnitudes yields 100-fold in brightness. In telescopes we are able to see magnitudes below the visible limit of 6. Most small scopes can view stars down to the 12th magnitude which is 100 times fainter then what can be seen with the naked eye. Sirius is the brightest star in the sky with a magnitude of -1.42. Venus one of the our solar systems planets can be as bright as -4.3. Full moon has a magnitude of -12.5 and the sun has a magnitude of -26.7.

A stars actual brightness is determined by it's size and surface temperature. Naturally how bright it appears to us has to due with these factors plus how distant is is from us. This is the stars visual magnitude. If a star was at a standard distance from us we could put a value on its actual brightness. This is known as a stars absolute magnitude. Normally when using a star chart it is showing a stars apparent visual magnitude rather then its absolute magnitude. The visual magnitude is how we normally perceive its brightness because it has the added factor of distance. Its the visual magnitude that enables us to identify individual stars from our fixed position here on planet earth.

Some small hot stars radiate as much light as larger cooler stars do. The color of a star is a good indication of its surface temperature. However a stars spectrum is the measurable method that astronomers use to determine a stars surface temperature. A spectrum is the rainbow of colors the stars light splits up into. We are all familiar with our own suns colors when passed through a glass prism.  All elements exhibit properties that are exclusive to them, it is like there finger prints that allows us to identify them. A stars spectrum is its finger print.

All the stars then can be categorized into seven common classes. These class are denoted by letters and subdivided by a decimal system. Star Classification

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