Vertical circle,observer's meridian and prime vertical
Answers
Prime vertical : In astronomy and astrology, the prime vertical is the vertical circle passing east and west through the zenith of a specific location, and intersecting the horizon in its east and west points. It is also known as the first vertical.
Vertical circle : In astronomy, a vertical circle is a great circle on the celestial sphere that is perpendicular to the horizon. Therefore, it contains the vertical direction, passing through the zenith and the nadir. There is a vertical circle for any given azimuth, where azimuth is the angle measured east from the north on the celestial horizon. The vertical circle which is on the east–west direction is called the prime vertical. The vertical circle which is on the north–south direction is called the local celestial meridian (LCM), or principal vertical. Vertical circles are part of the horizontal coordinate system.
observer's meridian - a meridian that passes through the observer's zenith. 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; "all points on the same meridian have the same longitude".
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