Glossary
Common words you will meet in star charts and astronomy apps.
- Altitude
- How high an object is above the horizon, measured in degrees from 0° (horizon) to 90° (straight up).
- Asterism
- A recognisable star pattern that is not an official constellation, such as the Big Dipper or the Summer Triangle.
- Conjunction
- When two objects appear close together in the sky, for example the Moon passing near a bright planet.
- Ecliptic
- The apparent path of the Sun across the sky over a year. The Moon and the planets always stay close to it.
- Light pollution
- Artificial light that brightens the night sky and hides fainter stars. A dark site outside town can reveal thousands more stars.
- Light-year
- The distance light travels in one year, roughly 9.46 trillion kilometres. It is a measure of distance, not time.
- Magnitude
- A scale of brightness where smaller numbers mean brighter objects. The faintest stars visible to the naked eye are around magnitude 6.
- Meteor shower
- A period when many meteors appear to come from one point in the sky, as Earth passes through debris left by a comet.
- Opposition
- When a planet is on the opposite side of Earth from the Sun. It is then closest, brightest and visible all night.
- Terminator
- The line between day and night on the Moon or a planet. Craters near it show the best shadows in a telescope.
- Zenith
- The point in the sky directly above your head.