| A | B |
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| Constellation | A group of stars that form a fixed pattern in the night sky |
| Reflecting Telescope | An instrument for viewing distant objects that uses a curved MIRROR at the back of its tube to gather light and produce an image |
| Refracting Telescope | An instrument for viewing distant objects that uses TWO CURVED LENSES to gather light and produce an image |
| Rotation | The spinning motion of an object on its axis- it takes 24 hours for the Earth to spin on its axis once |
| Revolution | The movement of an object around another object or point - it takes about 365 days for Earth to make one revolution around the Sun |
| Big Bang Theory | A hypothesis supported by data, that describes how the universe began with a huge explosion |
| Geocentric Model | A representation of the universe in which stars and planets revolve around Earth - Ptolemy proposed the geocentric model of the universe |
| Heliocentric Model | A representation of the relationship between the Sun and planets in which the planets revolve around a Sun - Copernicus hypothesized a heliocentric model of the solar system |
| Comet | A small object in space, made of ice, dust, gas and rock that orbits a star and that can form a gaseous tail |
| Meteor | A piece of rock or metal from space that enters Earth's atmosphere - a meteor appears as a streak of light, which is why it is also called a shooting star |
| Meteorite | The remaining material of a meteor that has landed on the ground |
| Gas Giant | A large planet that is made up mostly of gaseous and liquid substances, with little or no solid surface - Jupiter, Saturn, Uranus, and Neptune are gas giants |
| Terrestrial Planet | Any object in space that resembles Earth in size, in density, and in its mainly rocky composition |
| Nebula | A huge cloud of gas and dust found in space |
| Protostars | A concentration of matter found in space that is the beginning of a star. |
| Red Giant | A very large old red star that has greatly expanded and cooled as its fuel has begun to run out. |
| White Dwarf | A very small, dying star that gives off little light. |
| Black Dwarf | The cool, dark body that is the final stage in the life cycle of a low mass star. |
| Supernova | An exploding star |
| Neutron Star | The remains of a massive star that has exploded in supernova |
| Black hole | An extremely dense, invisible object in space whose gravity is so great that not even light can escape it |
| Axis | The imaginary line on which objects rotates |
| Star | A huge object in space, made up of hot gases, that shines by its own light |
| Planet | A large body in space that orbits a star and doesn't produce light on its own |
| Solar System | The sun and the planets and any other objects that orbit the sun. Also, stars and objects that revolve around it |
| Moon | A natural object that revolves around the planet |
