Orbit of dwarf planets - Pluto and Charon
Credit: SuperBlackCircle from YouTube

An orbit is when one object in the universe (for example a planet or a star) goes round another one without touching it.

Lots of things in the universe orbit others. The Moon orbits the Earth, the Earth orbits the Sun, the Sun orbits around the Milky Way and so on.

Orbits happen because of a mixture of gravity and momentum.

If, say, a spaceship starts to fly past the Earth, the momentum wants it go in a straight line, but the gravitational pull of the Earth tries to pull it down to the surface. If the spaceship is going very fast, the momentum is enough for the ship to fly past anyway, but if it is going slowly, the momentum isn't enough and the gravity will win and it will crash into the Earth.

You might want to have a look at this demonstration to see more clearly.

For things to orbit around each other the momentum and the gravity need to balance.

A lot of orbits are almost circular, but some are stretched out to make elliptical orbits.

Cosmology is the name we give to the study of the origin (the Big Bang) and evolution of the Universe. It’s looking at the universe on the large scale rather than the smaller objects within it. To learn more about the different aspects of cosmology explore the sections below.

Earth's Orbit

Credit: NASA

Solar Eclipse

Credit: Takeshi Kuboki

Lunar Eclipse

Credit: HeIios