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Right ascension (abbreviated RA; symbol α) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the Earth. [ 1 ] When paired with declination, these astronomical coordinates specify the location of a point on the ...
Alternatively to right ascension, hour angle (abbreviated HA or LHA, local hour angle), a left-handed system, measures the angular distance of an object westward along the celestial equator from the observer's meridian to the hour circle passing through the object. Unlike right ascension, hour angle is always increasing with the rotation of Earth.
For example, the proper motion results in right ascension in the Hipparcos Catalogue (HIP) have already been converted. [12] Hence, the individual proper motions in right ascension and declination are made equivalent for straightforward calculations of various other stellar motions. The position angle θ is related to these components by: [2] [13]
In the equatorial coordinate system, epoch 2000, the right ascension coordinates of these borders lie between 16 h 00 m 26.64 s and 18 h 57 m 49.50 s, while the declination coordinates are between +3.67° and +51.32°. [4] In mid-northern latitudes, Hercules is best observed from mid-spring until early autumn, culminating at midnight on June 13 ...
Astronomical coordinate systems. A star 's galactic, ecliptic, and equatorial coordinates, as projected on the celestial sphere. Ecliptic and equatorial coordinates share the March equinox as the primary direction, and galactic coordinates are referred to the galactic center. The origin of coordinates (the "center of the sphere") is ambiguous ...
Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the vernal equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Declination is measured northward or southward from the celestial equator, along the hour circle passing through the point in question.
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For imaging observations, the SDSS telescope used the drift scanning technique, but with a choreographed variation of right ascension, declination, tracking rate, and image rotation which allows the telescope to track along great circles and continuously record small strips of the sky. [10]