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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]
A star's spherical coordinates are often expressed as a pair, right ascension and declination, without a distance coordinate. The direction of sufficiently distant objects is the same for all observers, and it is convenient to specify this direction with the same coordinates for all.
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.
Regulus is the brightest star in the constellation of Leo (right tip, below is bright Jupiter in 2004). Regulus is a multiple star system consisting of at least four stars. Regulus A is the dominant star, with a binary companion 177" distant that is thought to be physically related.
Careful measurement of the star's position allows this angular movement, known as proper motion, to be calculated. 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.
See nuclear star cluster. conjunction A phenomenon during which two astronomical objects or spacecraft have either the same right ascension or the same ecliptic longitude as observed from a third body (usually the Earth), such that, from the observer's perspective, the objects appear to closely approach each other in the sky. constellation
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One red annotation is subtly shorter as the cosine of a star resting at 0° declination is 1, so such a star's east or west shift would not need to be multiplied by the cosine of its declination. The proper motion vector is μ, α = right ascension, δ = declination, θ = position angle.