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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]
Vega's proper motion is 202.03 ± 0.63 milliarcseconds (mas) per year in right ascension—the celestial equivalent of longitude—and 287.47 ± 0.54 mas/y in declination, which is equivalent to a change in latitude. The net proper motion of Vega is 327.78 mas/y, [83] which results in angular movement of a degree every 11,000 years.
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.
In the equatorial coordinate system, the right ascension coordinates of these borders lie between 18 h 14 m and 19 h 28 m, while the declination coordinates are between +25.66° and +47.71°. [12] The International Astronomical Union (IAU) adopted the three-letter abbreviation "Lyr" for the constellation in 1922.
These angles can be measured in time (24 hours to a circle) or in degrees (360 degrees to a circle)—one or the other, not both. Negative hour angles (−180° < LHA object < 0°) indicate the object is approaching the meridian, positive hour angles (0° < LHA object < 180°) indicate the object is moving away from the meridian; an hour angle ...
Conjunction in right ascension and conjunction in ecliptic longitude do not normally take place at the same time, but in most cases nearly at the same time. However, at triple conjunctions , it is possible that a conjunction only in right ascension (or ecliptic length) occurs.
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.
The vector algebra to derive the standard formula is equivalent to the calculation of the long derivation for the compass course. The sign of the angle is basically kept, north over east in both cases, but as astronomers look at stars from the inside of the celestial sphere, the definition uses the convention that the q is the angle in an image that turns the direction to the NCP ...