Altitude:the vertical distance of a celestial body measured vertically upwards from the horizon.
Aphelion:the most distant point from the Sun reached by a planet on an elliptical orbit in the Solar System.
Asteroid:A lump of rock orbiting the Sun. Most asteroids are found in a narrow belt situated between Mars and Jupiter.
Astronaut:Someone who travels trough space.
Astronomy:The scientific study of objects in space.
Atmosphere:Layer of gases surrounding a planet , moon or star.
Axis (of Spin):An imaginary line trough a rotating object , around which the object rotates.
Azimuth:the angle of a celestial body measured clockwise from the north in a direction parallel to the horizon.
Big Bang:The explosition that created the universe about 15,000 million years ago.
Big Crunch:One possible future end for the universe - the Big Bang in reverse.
Black Holean extremely superdense celestial body emitting no radiation.
Celestial Equator:the equator of the celestial sphere. It is a great circle and is the projection on the sphere of the Earth's equator.
Celestial Sphere:an imaginary sphere centered on the Earth and with the stars on its inside surface. It is useful for measuring co-ordinates (positions)of celestial bodies.
Cluster:A grouping of stars or galaxies held by gravity.
Comet:a collection of ice and rocky particles which orbits the SUN in a very elliptical path. Comets may display tails when close to the Sun.
Constellation:an artificial grouping of stars based on their apparent position in the sky.
Corona:the faint , outermost atmosphere of the Sun.
Crater:Circular depression in the surface of a planet or a moon caused by a meteorite impact.
Eclipse:The effect produced when one object in space passes in front of another and obscures it.
Ellipse:a closed figure which curves around two points (foci). It can be obtained by slicing obliquely trough a cone. Planetary orbits are all ellipse.
Equatorial mounting:a telescope mounting in which the telescope rotates about one axis parallel to the Earh's polar axis and also rotates at right angles to it. It allows the telescope to track the apparent motion of a elestial body in a single movement.
Equinox:when a day and night are equal. At these points in the year , the Sun is at those places where the celestial equator and the ecliptic cross one another.
Galaxy:an island of stars , together usually with dust and gas.
Gamma Rays:very short wave radiation , more penetrating thyan X-rays.
Gibbous:the phase of a celestial body that lies between the half illuminated disc and the full disc.
Gravity:the force with which bodies attract one another.It is quite different from magnetic attraction.
Great Circle:a circle on a sphere with a diameter equal to that of the sphere. The celestial equator is a great circle on the celestial sphere and the terrestial equator is a great circle on the Earth.
Heliosphere:The volume of space swept by charged particles from the Sun.
Hemisphere:One half of a sphere. The term usually applied to regions north or south of an equator.
Infrared Radiation:radiation with a wavelenght longer than red light.
Magnetic Field:the region of magnetic influence of a magnet or of a celestial body which acts like a magnet.
Mass:the amount of matter in an object. The Sun's mass is used as a standard for measuring the mass of stars and galaxies.
Matter:Anything that occupies space. There are three states of matter - gas , liquid and solid.
Meteor:a lump of rock or metal which comes from outer space and falls towards Earth's surface. Friction or rubbing against the air , causes it to heat up and emit light. A meteor ordinarly burns away before it drops down as far as the Earth's surface.
Meteorite:interplanetary material which has not been consumed completely in its passage trough the atmosphere and which therefore lands on the ground.
Meteoroid:a fragment of rock or metal in space.
Milky Way:the spiral galaxy which contains billions of stars including the Sun.
Moon:a natural satellite of a planet. Earth's moon is the Moon.
Nebula:a cloud of gas in space. Nebulae may be dark or if set glowing by nearby stars or stars embedded in them , they may be bright.
Neutron Star:a very dense compact star which often behaves like a pulsar.
Nova:a star which throws off a shell of hot gas and thereby appears brighter for short time , looking just as if a new star had been born.
Orbit:a path of onr body moving around another.
Orbital Period:the time taken for an object to make one complete orbit.
Parallaxthe apparent shift in position of a body when it is observed from two different positions.
Planet:a body attendant on another. In astronomy the term is usually used to describe a non-radiating body in orbit around a star.
Protostar:a very young star that has not begun to shine.
Quasar:a body which looks like a star but which emits far too much radiation to be one. It may be a bright core of a galaxy.
Radiation:short for 'electromagnetic radiation' , which ranges from radio waves to gamma-rays and includes light.
Solar Panels:Electronic devices that produce electricity when panel in sunlight.
Solar System:the sun and all the planets moons asteroids and comets that orbit around it.
Space:the volume between objects in the universe.
Star:a gaseous body which generates all the energy it emits.
Supercluster:a huge cluster that is itself made up of clusters of galaxies.
Universe:everything that exists.
Zodiac:the band of constellations trough which the sun , moon and planets appear to move.
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