| A | B |
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| time zone | any of the 24 divisions of the Earth's surface used to determine the local time for any given locality |
| hemisphere | either the northern or southern half of the earth as divided by the equator or the eastern or western half as divided by a meridian |
| season | one of the four divisions of the year (spring, summer, autumn, and winter), each of which has characteristic weather conditions |
| equinox | either of the two occasions when day and night are of equal length, around March 21 and |
| solstice | either of the two times of the year when the sun is at its greatest distance from the celestial equator |
| orbit | to travel around a planet (or other celestial body) in a roughly circular path |
| elliptical orbit | the path the earth travels round the sun (in a ‘flattened circle’) |
| leap year | every fourth year that contains an extra day (February 29th) |
| satellite | an object that orbits a planet |
| lunar month | the time taken for the moon to orbit the earth completely; 28 days |
| non-luminous | the time taken for the moon to orbit the earth completely; 28 days |
| eclipse | the partial or total blocking of light of one celestial body by another |
| solar eclipse | when the moon passes between the earth and the sun |
| total eclipse | a solar eclipse in which the moon completely blocks the sun’s light for a short period |
| lunar eclipse | when the earth passes between the sun and the moon |
| solar system | a system of planets or other bodies orbiting another star |
| asteroid | a piece of rock that orbits in the solar system and is not big enough to be a planet and is not a moon |
| meteorite | a meteor that does not burn up in earth’s atmosphere and impact’s earth’s surface |
| comet | a heavenly body that travels round the sun, leaving a long bright trail behind it |
| constellation | a group of stars that can be seen as a pattern in the night sky |
| revolution | an orbit of a planet around the sun |
| rotation | the turn of a planet around its axis |
| axis | an imaginary line around which an object rotates, e.g. the earth and other planets |
| totality | the event that occurs when a celestial body completely eclipses another celestial body |
| corona | the outermost part of the sun; located above the chromosphere |
| photosphere | the surface of the sun |
| chromosphere | the atmosphere of the sun; located above the sun’s surface |
| sunspot | a dark spot on the surface of the sun; seems to be related to magnetic storms |
| facula | a bright cloud of gas on the sun’s surface; usually accompanies sunspots |
| solar flare | a temporary flash created by solar storms that explode from the earth’s surface |
| solar prominence | huge stream of gas that extends past the sun’s atmosphere into the sun’s corona |
| solar wind | electrically charged particles from the sun, carried from the sun to earth’s atmosphere |
| aurora | the light show near earth’s pole that is caused by the solar wind and earth’s magnetic field |
| apparent magnitude | a star’s apparent brightness |
| absolute magnitude | a star’s actual brightness |
| dwarf star | a small or medium-sized star |
| giant star | a star that can be tens to hundreds of times larger and hundreds of times more luminous than the sun |
| super giant | a star that is hundreds of times larger than the sun and thousands of times brighter |
| parallax | a way of measuring the distance of stars by observing their apparent movement in relation to other stars |
| variable star | a star that regularly or repeatedly changes in brightness |
| pulsating variable star | variable star that goes through periods of brightening and swelling, then shrinking and diminishing |
| nova | a star that suddenly flares and becomes 100’s to 1000’s of times brighter than normal |
| nebula | a cloud of interstellar gases and debris |
| supernova | the death explosion of a massive star |
| neutron star | a star that has collapsed under its own gravity; it is composed of neutrons |
| pulsar | a neutron star that spins rapidly on its axis |
| black hole | area of extreme gravitational force that may result from the collapse of a massive supergiant |
| binary system | a star group containing 2 stars that revolve around each other |
| multiple star groups | a small star group of 3-4 stars |
| open star cluster | a group of several hundred to a few thousand stars with no particular arrangement |
| globular cluster | a group of several thousand to a million stars that are close to each other and arranged in the shape of a ball |
| galaxy | a huge star system that contains millions or billions of stars |
| Local Group | a group of more than 30 galaxies that includes the Milky Way |
| asteroid belt | the region between the orbits of Mars and Jupiter, where most of the asteroids are found |
| meteor | a meteoroid that lights up because of friction as it moves through the earth’s atmosphere |
| meteroid | a chunk of metal or stone that is moving toward earth’s atmosphere |
