Multiple-Star Systems - Constellations

gmaktub (57)in #science • 8 years ago (edited)

Multiple-Star Systems

You begin your trip by heading directly toward the star closest to the sun, Alpha Centauri. Although it is close by space standards, Alpha Centauri is still about 4.3 light years from Earth.

Because our sun is a single star system, astronomers believed for many years that most stars form individual star systems. For example, Alpha Centauri, when viewed from Earth, appears as a single speck in the sky. As you approach Alpha Centauri, however, you quickly discover that early astronomers were wrong. Alpha Centauri is not a single star at all, but three stars that make up a triple-star system. So Alpha Centauri is a multiple star system. In fact, only one of the stars, called Proximi Centauri, is actually the closest to Earth.

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As you continue your journey, you begin to realize that Alpha Centauri is not unusual. You discover that about half the stars in the sky have at least one companion star. Most of these stars are double star systems in which two stars revolve around each other. Double star systems are called binary stars (the prefix bi means two).

Thousands of years ago Arab shepherds discovered that about every three days a certain bright star suddenly became dim and disappeared, only to brighten again. In fear of this strange star, they named it Algol, the ghoul. Since your journey steers you by Algol, you will be able to discover the reason for Algol’s winking on and off. Algol is a binary-star system. One of Algol's stars is a small, bright blue star. It is visible from Earth. The other star is a large, dim, yellow star. It is not visible from Earth, so the Arabs could not have known of its existence. About every three days the large star passes between the smaller star and Earth, blocking off some of the smaller star's light. So every three days the smaller star appears to disappear.

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Constellations: Star Groups That Form Patterns

For Algol you can continue your jorney in any direction. One path may take you past the dog Star-Sirius-which is more than 8 light years from Earth. Another path may take you to the North. Star-Polaris-more than 700 light years from Earth. Polaris has long been an important star to navigators at sea because they knew if they steered toward Polaris they were heading north.

Polaris is at the end handle of group of stars called the Little Dipper. The Little Dipper, in turn, makes up the constellation of stars called Ursa Minor, or the Little Bear. Constellations are groups of stars in which people at one time thought they saw imaginary figures of animals or people at one time thought they saw imaginary figures of animals or people.

One of the best-know constellations is the Big Bear, or Ursa Major. The seven stars in the back end and tail of the Big Bear form the Big Dipper, which can be easily seen in the northern sky. Two bright stars in the cup of the Big Dipper are known as the pointer stars because they point toward Polaris.

On clear winter night, you can see the large constellation Orion, the Hunter. There are two bright star in this constellation: Betelgeuse and Rigel. Nearby are other constellations: Gemini, Canis Major, Or the Big Dog, and Canis Minor, or the Little Dog. Some of the summer constellations that are easy to recognize are Scorpios, Leo, and Virgo.

What constellations do you know?

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Novas

A Nova is a star that suddenly increases in brightness up to 100 times in just a few hours or days. Soon after brightens, the nova slowly begins to grow dim again. Astronomers believe that almost all novas are members of binary-systems. Gases from the companion star in the system occasionally strike the surface of the nova star. When this happens, a nuclear explosion results, and heat, light, and gases burst into space.

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Star Clusters

There are two types of star cluster. Open clusters such as the Pleiades are not well organized and contain hundreds of stars. Globular clusters, which are more common, are arranged in a spherical, or round, shape. Globular clusters, such as the clusters in the constellations Hercules, contain more than 100,000 stars. Star clusters appear to the unaided eye on Earth as one star or as a faint, white cloud.

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Composition of stars

By using the spectroscope, astronomers have found that almost all stars have the same general composition. The most common element in stars is hydrogen. Hydrogen is the lightest element. It makes up 60 to 80 percent of the total mass of a stars. Helium is the second most common element in a typical star. It is the second lightest element. In fact, the combination of hydrogen and helium make up about 96 to 99 percent of a star's mass. All other elements in a star total little more than 4 percent of the star's mass. These other elements often include oxygen, nein, carbon, and nitrogen.