How Big Are We In This Universe?

EARTH, MOON AND SUN

The Earth is the planet that we all live on.

As with all planets it is spherical in shape, although some ancient civilisations thought that the Earth was flat! It orbits around the Sun, and is the third planet out from the centre of our Solar System. The Sun is the star at the center of the Solar System!

The Moon is a natural satellite of the Earth, meaning that it orbits around the Earth. It is the only place outside of the Earth that humans have ever been! We can often see the Moon on a clear night, but it does appear to change shape during the 29 days it takes to orbit the Earth. 

Both the Earth and Moon orbit around the Sun, which is a star sitting in the centre of our Solar System. The Sun provides the light and heat that we have during the daytime, it is the energy it provides which keeps all things on Earth alive. The Sun is massive, and over a million Earth's could fit inside it!

It is the Earth's movement around the Sun once a year that leads to the four seasons of Spring, Summer, Autumn and Winter.

STAR

Stars come in huge range of different sizes. Neutron stars can be just 20 to 40 km in diameter, whereas white dwarf can be very similar in size to Earth's. The largest supergiants, on the other hand, can be more than 1500 times larger than our Sun. With the Sun having a diameter of 695,000 km, this means that in the extreme cases, we are looking at a star of over 1,000,000,000 km.

However, because supergiants are overly bloated stars in the final stages of their lifetime, they are far less concentrated (or dense) than a typical sun-like star, and so wouldn't actually weigh a great deal more than the Sun. Indeed, the famous red giant, Betelgeuse, is about 1000 times larger than the Sun, and yet only weighs about 15 times as much. With the atmospheres of large stars being so spread out, they tend to be a lot cooler and redder than a typical mid-life star.