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| the point at which Earth is farthest from the Sun; occurs around July 4 |
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| rocky and metallic object that revolves around the Sun but is too small to be called a planet; sometimes called minor planets, most are settled in the asteroid belt |
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| a historical instrument used by astronomers to determine the distance to stars; also used as a navigation tool |
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| a scientist who studies astronomy; different astronomers study different aspects of astronomy |
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| defined as the distance from Earth to the Sun, 150 million kilometres astronomy the branch of science that involves observations and explanations of events and objects that occur beyond Earth and its atmosphere |
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| the current theory that explains the formation of the Moon; it states that, approximately 4.5 billion years ago, the Moon was formed as a result of an object approximately the size of Mars colliding with Earth, causing less dense portions |
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| a circle on the celestial sphere; the extension of Earth's equator projected into the universe celestial sphere an imaginary rotating sphere upon which lie the all the objects in the universe |
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| refers to constellations around the pole; refers to constellations that never disappear below the horizon as Earth |
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| chunk of frozen matter that orbits the Sun in very long elliptical paths; some visit the Sun once; come from the Oort Cloud and the Kuiper Belt |
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| a group of stars that form a pattern |
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| the two dates when the Sun, on the ecliptic, crosses the celestial equator; occurring around March 21 and September 22, and known as the spring and fall equinoxes, respectively. On these days, the number of hours the Sun is above the horizon and below the horizon is equal. |
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