Our own star , the Sun, looks bigger and brighter
than all the other stars because it is much closer to us .
The Sun is a medium sized star.
It is bigger than all nine planets
in our solar system put together.
But there are stars that are thousands
of times bigger than the Sun.
The largest stars are supergiants
and very small stars are dwarfs.
There are many stars hotter than the Sun.
The hottest stars are bluish in color.
Stars with a medium temperature are yellowish
and the coolest stars are reddish.
Why do stars twinkle ?
As starlight travels through Earth's atmosphere
it makes some stars look like they are twinkling.
Stars live for billions of years.
Some fade away when they are ready to die; others explode.
After a star explodes it is called a supernova .
The light it gives off when it explodes
is brighter than a million stars.
A neutron star ( pulsar ) is a small body that spins
with great speed and sends out radio waves.
A black hole is the collapse of a supernova
under the force of its own gravity.
Nothing nearby can escape from the black hole .
Stars are so far from Earth that their distances
are measured in light years (how far light travels in a year).
The Sun is eight light minutes from us.
The next star is four light years away.
Some stars are billions of light years away.
The stars are always in the sky, even during the day.
We can't see them because the sun is too bright.
As the Sun starts to set and the sky darkens,
the stars seem to appear.