Bigger Stuff
Stars, galaxies and black holes.
Stars
The Sun is a star. There could be more than one septillion stars in the Universe and the Sun is quite a small and typical one.
A star is a super-hot ball of gas, mostly hydrogen. It is so massive that the hydrogen is squeezed by the star’s own gravity until it turns into another element, helium. This is nuclear fusion and it releases huge amounts of heat.
The intense heat inside a star balances the squeeze from its gravity, keeping the star from collapsing. It also makes the star shine, emitting visible light and radiation across the electromagnetic spectrum - `radio waves, infra-red, ultra-violet, x-rays and more.
Find out more about stars at Nasa Science - Universe - Stars.
Betelgeuse is over 1000 times the diameter of the Sun. It is 548 light years away. The picture above is the first time the surface of a distant star has been imaged using a very sophisticated radio telescope.
The Moon in the picture of Andromeda shows the sizes that the two objects would appear in the sky. Unfortunately, we can’t see the beautiful structure of our companinon galaxy without a powerful telescope - it is just too faint.
Galaxies
The septillion stars in the Universe are not spread out evenly. They are gathered together it vast spinning structures called galaxies.
The Solar System is in a galaxy called the Milky Way. We can’t see exactly what it looks like from the outside, but we know enough to be sure that it is is spiral galaxy. It would look similar to our closest large galatic neighbour, M32 Andromeda.
When astronomers looked at distant galaxies, the light showed they were all rushing away from us (and us from them). The scientists realised that this meant the Universe is expanding.
More about galaxies from Nasa Science - Universe - Galaxies
Black Holes
What is a black hole? This video from NASA’s Space Place, explains.
Nasa Science - Universe - Black Holes has even more information and scary facts.