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| A huge group of stars and other celestial bodies bound together by gravitational forces. There are spiral, elliptical, and irregularly shaped ones. |
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| A group of stars that, when seen from Earth, form a pattern. There are 88 of them such as Orion and Andromeda. |
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| A rapidly spinning neutron star, which are remnants of supernova, that emits energy in very short, regular burst. |
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| A very energetic, with a huge redshift, luminous, powerful distant star-like objects. It is believed to be the active core of a very distant galaxy. |
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| A glowing ball of gas where nuclear fusion, an atomic reaction in which many nuclei (the centers of atoms) combine together, results in the release of a lot of energy. |
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| A large celestial body that orbits a star and does not shine on its own. Gas planets are gaseous and terrestrial planets are land masses. |
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| The total amount of energy that radiates each second (including all wavelengths of electromagnetic radiation) from a star or galaxy. |
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| The full range of radiation, including: gamma rays, X-rays, UV rays, visible light, infrared, microwaves, and radio waves (in order of decreasing energy and increasing wavelength). |
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| A huge, diffuse cloud of gas and dust in intergalactic space. The gas is mostly hydrogen gas (H2). The birthplace of stars. |
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| Gigantic stars which after their main sequence, expand, cool and turn into super red giants. They next explode as a supernova and then turn into a neutron star or black hole. |
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| Stars like our sun, which after their main sequence turn into red giants. They next turn into a white dwarf and finally a tiny black dwarf. |
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| Stars with less than 40% of our sun, which after their main sequence turn into a white dwarf. |
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| A telescope which uses two lenses which magnify what is viewed; the large primary lens does most of the magnification. |
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| A Newtonian telescope which uses two mirrors to magnify what is viewed. |
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| A telescope is a metal dish that gathers waves with long wavelength from space. |
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| A scientific instrument that breaks up the light from a star into its component colors in order to identify which elements are present in that star. |
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| A unit of measure equal to the mean (average) distance from the Earth to the Sun, about 93 million miles (150 million km). |
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| A unit of measure of the distance that light can travel in one year in a vacuum, which is about 5,880,000,000,000 miles or 63,240 AU or 9.46053 x 10 to the 12th power kilometers. |
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| When an object turns around a central point or axis. One planetary day is defined as the time it takes a planet to rotate around its axis. |
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| When an object moves in orbits around another object. The Earth's revolution around the sun takes one year. |
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| Objects that orbit a planet or a moon. Many man-made and one natural one (the Moon) orbit the Earth. |
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| A large rocky object or very small planet (planetoid). Most orbit the Sun in a belt between Mars and Jupiter. |
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| A celestial body that orbits around the sun made up of an icy nucleus, a gaseous coma (water vapor, CO2, and other gases) and a tail (dust and ionized gases). |
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| Tiny stones or pieces of metal that travel through space. |
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| Also known as a shooting star, is a a meteoroid that has entered Earth's atmosphere. |
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| A meteor that has fallen to Earth. They can be either stone, iron, or stony-iron. |
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| A moon which appears as an entire circle in the sky; it is illuminated by the Sun, when the Moon is on the opposite side of the Earth from the Sun. |
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| A moon that looks like half a circle. This moon has completed 25% of an orbit around the Earth and one fourth of the moon's surface is visible from Earth. |
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| Moon is shrinking in size. |
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| A moon which is part way between a half moon and a new moon, or between a new moon and a half moon. |
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| The phase of the moon when the moon is not visible from Earth, because the side of the moon that is facing us is not being lit by the sun. |
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| An object that has collapsed to such a degree that light cannot escape from its surface due to being trapped by the intense gravitational field. |
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| The origin of the solar system began with a near collision of the sun and a large star. |
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| The origin of the solar system began with rotating clouds of dust and gas that formed the sun and other celestial objects. |
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| The origin of the universe resulted from a magnificent explosion spreading mass, matter and energy into space. |
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| The universe is continuously renewed with galaxies moving outward and new galaxies replacing the older ones. |
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| A unit of measure for large distances equaling to 3.26 light-years. |
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| An instrument that gathers visible light and focuses it to produce images. |
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| The inner (1) core where fusion takes place is surrounded by the surface (2) photosphere. The reddish (3) chromosphere and finally the shining (4) corona visible only in an eclipse. |
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