- Types:
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celestial equator, equinoctial, equinoctial circle, equinoctial line
the great circle on the celestial sphere midway between the celestial poles
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ecliptic
the great circle representing the apparent annual path of the sun; the plane of the Earth's orbit around the sun; makes an angle of about 23 degrees with the equator
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equator
an imaginary line around the Earth forming the great circle that is equidistant from the north and south poles
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celestial horizon, horizon
the great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth
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hour circle
a great circle on the celestial sphere that passes through both celestial poles
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line of longitude, meridian
an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator
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vertical circle
a great circle on the celestial sphere passing through the zenith and perpendicular to the horizon
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observer's meridian
a meridian that passes through the observer's zenith
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prime meridian
meridian at zero degree longitude from which east and west are reckoned (usually the Greenwich longitude in England)
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magnetic meridian
an imaginary line passing through both magnetic poles of the Earth
