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How are stars formed?

A star is a celestial body that is composed of gas. It derives its energy from thermonuclear reactions in its hot dense core. The sun is a typical star.

A star’s mass determines its luminosity, surface temperature, size and other properties as well as its lifetime. The higher the mass, the brighter and hotter, and also the shorter its life. Stars begin their lives as very thin clouds of hydrogen gas. As each cloud shrinks, the centre grows very hot due to the atoms of gas being pushed together. Eventually the clouds become so hot that they shine as stars.

Stars are usually formed in clusters, just as the sun probably was, but its companion stars have drifted and can’t be identified. Although star formation is still appearing in our galaxy, in others where there is little gas left there are no stars being formed.

It may appear that out in space stars actually seem to twinkle; this is not the case. When their light passes through the earth’s atmosphere, it is made to flicker by the hot and cold ripples of air.

Although stars are only visible only at night, they are still in the sky during the day; the blue sky just does a good job at hiding them. When the Sun sets the blue fades away and the stars can then be seen. A powerful telescope can still see the stars, even when the sun is shining. Even the planet Venus can be seen with the naked eye if it is bright enough. Some keen astronomers have claimed to have seen Jupiter and Mars. The sky would have had to be perfectly transparent for this to happen and is fairly unlikely.

Some stars are brighter than others are; this is due to the fact that many stars give out more light. Most of the brighter stars are closer to the Earth and then even a dim star can appear brighter than a very luminous distant one. The nearest star to the Sun is approximately 4.3 light years away. The star’s brightness is called the ‘magnitude’. The brightest stars are measured as having a magnitude of 0, while the dimmest stars are scaled as a 6.

Dying Stars
Not all stars live for the same length of time. Dimmer stars tend to use less fuel than the brighter ones and therefore can continue their lives for many millions of years, often as many as 10,000. Hot and shinier stars all tend to burn out sooner, dying after just a few million years. Then they explode, leaving wreckage floating in space. Others gradually blow their surfaces outward like a red-hot cloud in the ‘red-giant’ stage. In the far future, the sun may become a red giant.