Site Glossary

The magnitude of gravitational acceleration, approximately 9.8 m/s² near Earth’s surface.

The time taken for the Solar System to orbit once around the centre of the Milky Way.

A massive collection of stars, gas, dust, planets, and dark matter held together by gravity.

A group of galaxies bound together by gravity.

a graph showing orbital speed at different distances from a galaxy's centre.

The highest-energy electromagnetic waves with the shortest wavelengths.

a short, extremely energetic burst of gamma radiation from an astronomical source.

an orbit in which a satellite appears stationary above one point on Earth's equator.

A large, luminous star that has exhausted much of its core hydrogen.

the steepness of a line on a graph.