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|Table of Contents||Enchanted Learning
All About Astronomy
|Our Solar System||Stars||Glossary||Printables, Worksheets, and Activities|
|The Sun||The Planets||The Moon||Asteroids||Kuiper Belt||Comets||Meteors||Astronomers|
|Lifecycle||Nuclear Fusion||Brightest Stars||Galaxies||Other Solar Systems||Constellations||Why Stars Twinkle|
|Birth||Death||Star Types||Closest Stars||Nebulae||Major Stars||The Zodiac||Activities, Links|
The composition of stars is studied using spectroscopy in which their visible light (the spectrum) is studied.
GROUPS OF STARS
In the universe, most stars occur in groups of at least two stars. Two stars that are locked in elliptical orbit around their center of mass (their barycenter) are called a binary star system. About half of all stars are in a binary star system.
A globular star cluster is a spherical group of up to a million stars held together by gravity. These remote objects lie mostly around the central bulge of spiral galaxies.
WHY DO STARS TWINKLE?
The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation). Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere.
Stars (except for the Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).
Stars closer to the horizon appear to twinkle more than stars that are overhead - this is because the light of stars near the horizon has to travel through more air than stars overhead and subject to more refraction. Also, planets do not usually twinkle - they are big enough that this effect is not noticeable (except when the air is extremely turbulent).
Stars would not appear to twinkle if we viewed them from outer space (or from a planet/moon that didn't have an atmosphere).
Stellar wind is ionized gas that is ejected from the surface of a star (including the Sun). Older (evolved) stars give off stronger stellar winds than younger stars.
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