It is a huge glowing globe of gas. It shines by its own light, rather than reflecting light (like planets) or glowing from heat friction (like meteors). Seen from earth, stars look like points of light. A normal star's size and temperature can be judged from its colour and brightness:

• A RED STAR is the coolest type of star (about 2,600-3,000 degree C). The red colour is produced by the relatively cool gases near the surface of a very large stars or by the cooling surface of dying stars.
• A YELLOW STAR is hotter than the red star (about 5,000-11,000 degree C).
• A BLUE STAR is very hot and very bright star (about 19,000-30,000 degree C). Often a new star.

All stars are born in huge clouds of gas and dust. The gases and dust swirl around and form into clumps and the clumps start to shine. Stars become unstable after sometime. Some stars shrink into small and very dense stars known as White dwarfs and others explode and turn into black holes. A black hole cannot be seen because nothing can escape a black hole. Anything that comes near it is pulled in and disappears. The life of a star is about 10,000,000,000 years.

Stages of the Star

• A white dwarf is a dying star that has collapsed to planet size. It burns brightly.
• A giant star is a star that is much bigger than the size of the sun. It burns with all the brightness of at least one hundred suns.
• A super giant is a star which is billions of kilometer in diameter. It burns thousands of times brighter than our sun.
• A pulsating star is a star which expands and shrinks periodically.
• A nova is a star whose surface layer explode. The star survives and explodes repeatedly.
• A supernova is a huge explosion which release as much energy in 24 hours as our sun would in a billion years. It can outshine hundreds of billions of stars.

Star Brightness

The brightness of stars can be described in two ways: actual and apparent. Actual brightness can be caused by the difference in the temperature between the stars themselves. Apparent brightness depends upon how bright the star appears from Earth.

Distance of the Stars

Sun is the nearest star. Its light reaches us in about 8 minutes. Other stars are so far away that their light takes years to reach us. The distance of the star from the earth is too far to be measured directly. The distance of the star can be measured by light year. LIGHT YEAR is a distance light travels in one year at about 186,000 miles per second. For example:

• Sirius is 8.7 light year.
• Altair is 16 light year.
• Vega is 25 light year.
• Antares is 520 light year.
• North Star is 400 light year.
• Orion constell is 1,300-1,500 light year.
• Globular cluster Hercules is 23,500 light year.
• Quasar (farthest body visible) is 10 billion light year.