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Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the March equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Right ascension is measured eastward up to 24 h along the celestial equator from the primary direction.
The equation of time is obtained by substituting the result of the right ascension calculation into an equation of time formula. Here Δ t ( M ) = M + λ p − α [ λ ( M )] is used; in part because small corrections (of the order of 1 second), that would justify using E , are not included, and in part because the goal is to obtain a simple ...
The longitude of the ascending node, also known as the right ascension of the ascending node, is one of the orbital elements used to specify the orbit of an object in space. Denoted with the symbol Ω , it is the angle from a specified reference direction, called the origin of longitude , to the direction of the ascending node (☊), as ...
Newcomb gives the Right ascension of the fictitious mean Sun, affected by aberration (which is used in finding mean solar time) as [10] τ = 18 h 38 m 45.836 s + 8 640 184.542 s T + 0.0929 s T 2. Authors citing this expression include McCarthy & Seidelmann (p. 13) and the Nautical Almanac Offices of the United Kingdom and United States (p. 73).
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 change μ α, which must be multiplied by cosδ to become a component of the proper motion, is sometimes called the "proper motion in right ascension", and μ δ the "proper motion in declination". [11] If the proper motion in right ascension has been converted by cosδ, the result is designated μ α*.
(The above formula is related to a reasonably simple and accurate calculation of the Equation of Time, which is described here.) More complicated algorithms [16] [17] correct for changes to the ecliptic longitude by using terms in addition to the 1st-order eccentricity correction above. They also correct the 23.44° obliquity which changes very ...
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.