stars

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The thousands of twinkling stars that we observe in the clear night sky are part of our Milky Way. Some of the stars that we see are bright whereas others are faint. Stars radiating different colours such as blue, white, yellow and reddish can be seen in the sky. We also see stars with varying brightness (luminance).

When we look at stars in the night sky, we are looking back in time. Many stars formed billions of years ago. The star-light that reaches to earth left those faraway stars some time ago, ranging from a few minutes ago (The sun) to four year ago (Alpha centuari, the sun nearest star neighbor). The light see today from the Andromeda galaxy is left it two and half million years ago.

Stars contain mostly Hydrogen and Helium. They create energy by fusion of hydrogen and turning in to helium and resulting energy of starlight. Generally, the surface temperature of stars ranges from 3500° C to 50000° C. The colour of stars changes according to their temperature.

THE BIRTH PLACE OF STARS : NEBULAE  

Stars are born in an enormous cloud of interstellar dust and hydrogen gas called nebulae. Nebulae forms when star die. When the end comes for star, its outer layer will heat, swell and eventually blow of. The hot, dead core creates a glowing nebula, which will turn become a nursery for new stars.  

Type of stars:-

a) Sun-like stars: These stars can be slightly smaller or bigger than the sun. But there is a lot of difference in their temperatures. Examples : stars like Sirius, Alpha Centauri.

b) Red Giants: The temperature of these stars ranges between 3000°C and 4000°C. But their luminance can be 100 times that of the sun. Their diameter is 10 to 100 times that of the sun and they are red in colour.

c) Super Nova: These are even brighter and larger than the red giant stars. Their temperature is between 3000°C to 4000°C but their diameter can be more than a hundred times greater than that of the Sun.

d) Binary or Twin Stars : More than half of the stars in sky are binary stars. They consist of two stars that revolve around each other. At times, three or four stars that revolve around each other have also been located.

e) Variable Stars : The luminance and shape of these stars is not stable. They are constantly contracting or expanding. When a star expands, it emits less energy and at such times its brightness decreases. As against this, when a star contracts, its surface temperature increases and the star emits greater energy and appears brighter. For example, Polaris (Pole Star).

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