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Astronomy terms meaning :



Annual Motion – the Earth’s orbital motion around the sun every year

Asteroid Belt – the area between the inner and outer planets that is filled with asteroids

Asteroids – chunks of rock that vary in size from very large (1030km diameter) to very small. About 3000 asteroids have been discovered

Astronomical Unit – the distance from the Earth to the Sun (150 million km) used to measure distances within the solar system

Astronomy – the study of the universe and all of the bodies that appear in the skies

Atmosphere – a layer of air between the Earth and outer space

Axis – an imaginary straight line that an object or body rotates, or seems to rotate, around

Binary Stars – when two relatively close stars revolve around each other, often appearing as single stars because they are so far away from Earth

Black Hole – an intense gravitational field created when a star runs out of fuel and collapses. Nothing, not even light can escape its pull

Blue Moon – the second full moon in a month

Celestial Equator – an imaginary line in the sky directly above the Earth’s equator in the heavens surrounding the Earth

Comet – a large ball of ice, dust, rock and gas that orbits the Sun, circling the dark edges of the Solar system

Crater – a hole created on the surface of an object or body, made by falling meteorites or by erupting volcanoes

Emit – to send or to give out

Eclipse – Comes from the word meaning ‘hidden’. There are two types – solar and lunar. A solar eclipse is when the moon passes in front of the sun either partially or totally covering it. A lunar eclipse is when the Earth passes between the sun and moon, creating a shadow on the moon which makes it appear dark on Earth.

Ecliptic – the apparent annual path of the Sun, as seen from the Earth. It is called the ecliptic because eclipses only occur when the Moon is on or near this path.

Equator – an imaginary circle around the centre of the Earth, separating the northern hemisphere from the southern hemisphere

Equinox – the two days in which the day on earth is equally divided between 12hrs of sunlight and darkness, caused as the sun passes the celestial equator at one of two points – on or around the 21st of March and 23rd of September

Galaxy – a spiral island of stars in space – our galaxy is called the Milky Way

Gibbous – a phase of the Moon’s cycle when more than half the moon but not the entire face is illuminated

Hemispheres – either the north half or the south half of the Earth divided by the equator, or the east half or west half divided by the prime meridian

Inner Planets – the four hard rocky planets – Mercury, Venus, Earth, Mars – closest to the Sun

Light Year – the distance light travels in a year, approximately 9.5 trillion km. Used to measure distances in space

Lunar Month – the time it takes the Moon to go around the Earth (27 1/3 days)

Magnitude – a six class scale used to measure the brightness of stars. The brightest are 1st magnitude, the faintest are 6th.


Meteors are what enter Earth’s atmosphere and burn up – aka ‘shooting star’

Meteorites are larger meteors that make it to the surface

Meteroids are rocks which are in space as small as sand but smaller than asteroids and sometimes enter Earth’s atmosphere

Orbit – the path of a planet or other heavenly body as it revolves around another body in space

Outer planets – the four giant, gaseous planets – Jupiter, Saturn, Uranus, Neptune – that orbit the Sun

Planets – large bodies that can only be seen by reflected light as they revolve around the Sun. Comes from the Greek word meaning ‘wanderer’

Pole Star – a bright star, also known as Polaris, useful as a benchmark as it always stays in the same position in the northern sky

Revolution – the motion of a planet as it orbits around the Sun

Rotation – the motion of a planet satellite, or the Sun, as it turns on its axis. For example, the Earth’s rotation takes 24 hours (23 hrs 56 mins)

Satellite – a man-made or heavenly body (moon, etc) that orbits around a larger object

Solar Noon – the time of the day when the Sun casts its shortest shadow and shadows face true north

Solstices – the two days in which the Sun reaches its highest and lowest points in the sky at noon, occurring at or about June 21st and December 21st

Star – a gaseous body that produces its own energy, releasing it as light and heat

Sublimate – turn directly from a solid to a gas

Sun – the closest star to Earth, measuring more than a million kilometers across

Sundial – a device that uses shadow to tell time

Universe – everything that exists: the Earth, Sun, Moon, satellites, stars, asteroids, all the galaxies and space in between

Waning Moon – when the Moon grows gradually less illuminated when passing from Full Moon to New Moon

Waxing Moon – when the Moon grows gradually more illuminated when passing from New Moon to Full Moon

Year – the time it takes for a planet to go all the way around the Sun ie. Earth is 365 days, Uranus is 84 earth years


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