Astronomers have pieced together the story of how stars form by observing the many different stars that can be seen from Earth. Stars change throughout their life and eventually die.
A starís birthplace
New stars form
within vas clouds of gas and dust, called nebulae. Some nebulae are bright and
some are dark. Dark nebulae are made mostly of dust and so they blot out the
light of stars behind them. They look like dark patches of starless sky.
nebulae can only be seen through a telescope, but you can see the nebula M42,
with binoculars. It lies in Orion. There is another nebula dark nebula, called
the Horseís Head Nebula is silhouetted against a bright nebula. The Horseís
Head also lies in the constellation Orion. You need a powerful telescope to see
Another bright Nebula is the Trifid Nebula. The gases in it are so hot that they make the surrounding gas clouds glow in beautiful shades. Hydrogen glows pink, while oxygen glows green-blue. You need a good telescope to see it.
Before stars begin to form in a nebula, the clouds of gases and dust swirl around and around. They then form into clumps which grow larger and larger.
something causes the clouds to collapse. Some astronomers think that this might
happen when the clouds pass through the arms of a spiral galaxy. Some
suggest that the shock waves from an exploding star might start the collapse.
the cloud collapses, the temperature rises inside. After tens of thousands of
years of collapse, a hot core forms. The core gets hotter and hotter until
nuclear reactions begin inside, making the clump of gases start to shine. The
new star has been born. Most new stars are hot and bright, but some are cooler
At first, most
new stars burn very brightly. They appear either blue or white. This state
continues for millions of years.
get older, they settle down and shine less brightly but more steadily, like our
Sun. The Sun is only halfway through its lifespan of around 10,000 million