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| The angular diameter or apparent size of an object as seen from a given position is the “visual diameter” of the object measured as an angle. |
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| An eclipse during which the Moon is directly in front of the Sun but its angular size is not large enough to fully block the Sun; thus, a ring of sunlight is still visible around the Moon's disk |
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| The amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic plane |
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| The imaginary sphere on which objects in the sky appear to reside when observed from Earth |
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| A region of the sky; 88 official constellations cover the celestial sphere |
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| The Sun's apparent annual path among the constellations |
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| Broadly speaking, energy is what can make matter move. The three basic types of energy are kinetic, potential, and radiative |
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| The speed necessary for an object to completely escape the gravity of a large body such as a moon, planet, or star |
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| Any of the ancient Greek models that were used to predict planetary positions under the assumption that Earth lay in the center of the universe |
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| Sun-Centered Model. Initiated by Copernicus, this model was based on the idea that the planets are in orbit around the Sun rather than the Earth |
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| Energy of motion, given by the formula 1/2mv^2 |
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| The amount of time that has passed since the light we see from a distant object was emitted |
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| The product of an object's mass and velocity |
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| North Celestial Pole (NCP) |
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| The point on the celestial sphere directly above the Earth's North Pole |
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| The point at which an object orbiting the Sun is closest to the Sun |
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| Energy stored for later conversion into kinetic energy |
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| The concept that the mass of a body is a measure of its energy content |
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| The spinning of an object around its axis |
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| Eclipse that occurs when the Moon's shadow falls on the Earth, which can occur only at new moon; may be partial, total, or annular |
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| The time required for a complete cycle of lunar phases, which averages about 29.5 days |
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| the time between two consecutive appearances of a body at the same point in the sky relative to the Sun as seen from the Earth |
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| Tides are the rise and fall of sea levels caused by the combined effects of the rotation of the Earth and the gravitational forces exerted by the Moon and the Sun |
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| The point directly overhead, which has an altitude of 90 degrees |
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