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| The angular distance between the horizon and an object in the sky |
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| momentum attributable to rotation or revolution. The angular momentum of an object moving in the sky moving in a circle of radius r is the product m*v*r |
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| The average distance of the Earth from the Sun, which is about 150 million km |
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| The extension of the Earth's equator on to the celestial sphere |
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| The principle that energy can be neither created nor destroyed, but can only change from one form to another |
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| The principle that, in the absence of net force, the total momentum of a system remains constant |
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| Occurs when one astronomical object casts a shadow on another or crosses our line of sight to the other object |
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| A type of oval that happens to be the shape of bound orbits |
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| either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length |
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| One of two special points within an ellipse that lie along the major axis. When one object orbits a second object, the second object lies at one focus of the orbit |
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| Gravitational potential energy |
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| Energy that an object has by virtue of its position in a gravitational field; an object has more gravitational potential energy when it has a greater distance than it can potentially fall |
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| States that the orbit of each planet about the Sun is an ellipse with the Sun at one focus |
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| States that, as a planet moves around its orbit, it sweeps out equal areas in equal times. Tells us that a planet moves faster when it is closer to the Sun than when it is farther from the Sun. |
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| States that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun, which tells us that more distant planets move more slowly in their orbits |
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| The distance that light can travel in one year, which is 9.46 trillion km |
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| A half-circle extending from your horizon (altitude 0 degrees) due south, through your zenith, to your horizon due north |
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| Newton's First Law of Motion |
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| In the absence of a net force, an object moves with constant velocity |
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| Newton's Second Law of Motion |
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| Newton's Third Law of Motion |
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| For any force, there is always an equal and opposite reaction force |
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| Approximately equal to 3.26 light-years; it is the distance to an object with a parallax angle of 1 arcsecond |
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| Energy carried by light; the energy of a photon is Planck's constant times is frequency, or h*f |
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| The orbital motion of one object around another |
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| About 27.25 days, the time required for the moon to orbit the Earth once |
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| Sidereal period (of a planet) |
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| A planet's actual orbital period around the Sun |
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| The rate at which an object moves. Its units are distance divided by time, such as m/s or km/hr |
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| The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force exerted on one body by a second body is not constant across its diameter |
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| The combination of speed and direction of motion; it can be stated as a speed in a particular direction, such as 100 km/hr due north |
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