Glossary
Here you will find the definitions of a lot of the terms that you will hear about when you study the planets and space in general.
Asteroid
A rocky body in space that orbits the Sun. Asteroids can be up to 1 km in diameter or a lot smaller. Many appear in the main asteroid belt.
Atmosphere
The atmosphere typically surrounds a planet but it can surround another large body in space. It is the gaseous mantle of a planet or other body.
Big Bang
The big bang is the event that is believed to have triggered the creation of the universe.
Black hole
A black hole is a massive region in space that is so dense that no light or radiation can escape from it.
Comet
A comet is a small icy object that orbits the Sun in a very long eccentric orbit.
Constellation
A constellation is a group of stars that are named after a mythological character or object. Examples include Gemini, Orion, Sagittarius, etc.
Corona
The corona is the outermost part of the Sun’s atmosphere. This area can be seen during solar eclipses.
Cosmology
Cosmology is the study of the universe as a whole. It includes all individual disciplines.
Day
A day is the total time that it takes a planet to complete one full spin on its axis.
Eccentricity
This is a term that you will often hear when studying orbital paths. An eccentric orbit occurs when a planet, moon or object does not orbit in a perfect circle.
Equator
The equator is an imaginary line that is drawn down a planet where there is an equal distance at all point on the line between the north and south poles of the planet.
Galaxy
A collection of stars dust and gas that are held together by gravity. Different galaxies can be different shapes such as elliptical, spiral or irregular.
Gas giant
The gas giants refer collectively to the four outermost planets in our solar system. These are Jupiter, Saturn, Uranus and Neptune.
Gravitation
Gravitation is the force of attraction between all particles of matter in the known universe.
Hubble Space Telescope
The Hubble Space Telescope is a large telescope that we launched into space so that we can view objects many light years away from our own planet.
Inferior planet
An inferior planet is one that is closer to the Sun from the position of the observer. So from the Earth, Mercury and Venus are called inferior planets.
Luminosity
This is the total brightness of an object.
Lunar eclipse
A lunar eclipse occurs when the Earth lies directly between the Sun and the Moon.
Mass
Mass is the amount of matter that is contained within a body.
Meteor
A meteor is a small piece of rock that travels through space which when it enters a planet’s atmosphere it burns up.
Meteorite
A meteorite is a meteor that is typically larger in size because a meteorite does not burn up in the atmosphere of a planet, it will actually hit the surface of the planet.
Milky Way
This is the galaxy that we are a part of which also contains billions of other objects including our own planet.
Moon
Our own natural satellite is called the Moon.
Orbit
An orbit is the path that one object takes around another object in space.
Perihelion
This is the closest a celestial body such as a planet gets to the Sun during its orbit.
Planet
A planet is a body that is in orbit around the Sun or another star.
Reflecting telescope
This is a type of telescope that works by a mirror collecting light and magnifying it.
Refracting telescope
This is similar to a reflecting telescope but a lens is used which provides a stronger magnification.
Satellite or Moon
A moon (sometimes called a satellite) is a body in the orbit of a larger parent body. Typically a moon will orbit a planet.
Solar eclipse
A solar eclipse occurs when the Moon passes directly between the Sun and the Earth and a shadow is cast on the Earth.
Solar system
The solar system is the group of objects that contains the Sun and any other object that is subject to the gravitational pull of the Sun. This can include planets, moons, asteroids, dust, gas, etc.
Star
A star is a massive luminous ball of plasma that produced light and energy from its core through a series of nuclear reactions.
Sun
The Sun is the star which the Earth and the planets within our solar system orbit around.
Sunspots
These are darker, cooler patches that appear on the surface of the Sun and appear in 11 year cycles.
Superior planet
A superior planet is a planet that is further away from the Sun than the Earth.
Terrestrial planets
The terrestrial planets are the four planets that are closest to the Sun. These are Mercury, Venus, Earth and Mars.
Universe
The universe is considered as everything that has existed, currently exists and will exist in the future.