Astronomy and Physics Terms

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Solstice

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The time or date (twice each year) at which the sun reaches its maximum or minimum declination, marked by the longest and shortest days.

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Equinox

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The time or date (twice each year) at which the sun crosses the celestial equator, when day and night are of approximately equal length.

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Comet

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A celestial object consisting of a nucleus of ice and dust, and when near the sun, a “tail” of gas and dust particles pointing away from the sun.

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Asteroid

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A small rocky body orbiting the sun, found mainly between the orbits of Mars and Jupiter in the asteroid belt.

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Surface Area

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The total area that the surface of an object occupies.

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Gravity

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The force that attracts a body toward the center of the earth, or toward any other physical body having mass.

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Density

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The degree of compactness of a substance, calculated as mass per unit volume.

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Pollution

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The presence in or introduction into the environment of a substance which has harmful or poisonous effects.

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Universe

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All existing matter and space considered as a whole; the cosmos.

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Galaxy

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A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.