فهرس مصطلحات

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Absorption Lines

    Thin dark lines across a spectrum which indicate the presence of chemical element in the light source.

Accretion Disk

     A structure formed by material being drawn into a rapidly rotating black hole.

Asteroid

     A lump of rock orbiting the sun. Most asteroids are found in a narrow belt situated between Mars and Jupiter.

Astronomy

      A scientific study of objects in space.

Atmosphere

      Layer of gases surrounding a planet, moon, or star.

Axis (of spin)

       An imaginary line through a rotating object, around which the object rotates.

Big Bang

       The explosion that created the universe about 15 billion years ago.

Big Crunch

       One possible future end for the universe-the big bang in reverse.

Black hole

        An infinitely dense object formed initially by the collapse of a massive star. The gravity of a black hole is so strong that not even light can escape from it.

Celestial Equator

        A projection of Earth’s equator out into space, used as a baseline for positioning stars.

Celestial pole

       Projection of Earths north or South Pole into space, for use as a reference point.

Celestial sphere

       The appearance of the stars from Earth- as though they were set into a black sphere around the planet.

Chromosphere

        The Sun’s inner atmosphere.

Cluster    

        A grouping of stars or galaxies held by gravity.

Comet

       An object composed of snow and dust that orbits the sun. If a comets approaches the sun it forms a tail of gas and dust particles.

Constellation

        A grouping of bright stars seen in Earth’s sky. In most cases the grouping is a trick of perspective and the stars are a long way apart

Co/orbital 

      Sharing an  orbital path with another object.

Core 

      The central region of a planet, star, or galaxy.

Corona 

      The sun's outer atmosphere.

Crater

     Circular depression in the surface of a planet or a moon caused by a meteorite impact.

Crust 

     The surface layer of a rock planet or moon.

 Eclipse 

      The effect  produced when one object in space passes in front of another and obscures it.

Ecliptic 

     The sun's apparent path around the celestial sphere during a year.

Flyby 

     The path of a space probe that obtains information by flying past, or orbiting, a moon or planet.

Galaxy 

      A large grouping of stars  held together by gravity. Galaxies can be spiral, elliptical (oval) , or irregular in shape.

Gravity 

    An attractive force that is a property of mass.

Light year

     The distance traveled by light in one year -used to measure distance between stars and galaxies.