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Right ascension is measured eastward up to 24 h along the celestial equator from the primary direction. 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]
The dates at which the nodes line up with the celestial equinoxes are not the same as the dates when the moon actually gets to the lunistice position, and can occur at any time of the year. This is both because of the fluctuation in inclination mentioned above, and because the moon has to arrive at right ascension 6 hours or 18 hours (90° or ...
The exact geocentric conjunction in right ascension took place at 07:58 UTC on this day with an angular separation of 3 degrees. It was perhaps the brightest star-like object in recorded history, which went in closer conjunction with the moon.
In this case, the longitude is also called the right ascension of the ascending node (RAAN). The angle is measured eastwards (or, as seen from the north, counterclockwise) from the FPA to the node. [2] [3] An alternative is the local time of the ascending node (LTAN), based on the local mean time at which the spacecraft crosses the equator.
It represents the ascension of the Moon in its precessional orbit around the Earth, also referred as the north lunar node, and along with Ketu, is a "shadow planet" that causes eclipses. Despite having no physical existence, Rahu has been allocated the status of the planet by ancient seers owing to its strong influence in astrology.
For instance, the Astronomical Almanac for 2010 lists the apparent geocentric position of the Moon on January 1 at 00:00:00.00 Terrestrial Time, in equatorial coordinates, as right ascension 6 h 57 m 48.86 s, declination +23° 30' 05.5". Implied in this position is that it is as projected onto the celestial sphere; any observer at any location ...
Like right ascension in the equatorial coordinate system, the primary direction (0° ecliptic longitude) points from the Earth towards the Sun at the March equinox. Because it is a right-handed system, ecliptic longitude is measured positive eastwards in the fundamental plane (the ecliptic) from 0° to 360°.
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]