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A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol ″, [2] is a unit of angular measurement equal to 1 / 60 of a minute of arc, 1 / 3600 of a degree, [1] 1 / 1 296 000 of a turn, and π / 648 000 (about 1 / 206 264.8 ) of a radian.
Gauss himself stated the constant in arc seconds, with nine significant digits, as k = 3548″.187 61. In the late 19th century, this value was adopted, and converted to radian, by Simon Newcomb, as k = 0.017 202 098 95. [6] and the constant appears in this form in his Tables of the Sun, published in 1898. [7]
A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle in which one full rotation is 360 degrees. [ 4 ] It is not an SI unit —the SI unit of angular measure is the radian —but it is mentioned in the SI brochure as an accepted unit . [ 5 ]
60 arc-minutes (′) in one degree; 60 arc-seconds (″) in one arc-minute; To put this in perspective, the full Moon as viewed from Earth is about 1 ⁄ 2 °, or 30 ′ (or 1800″). The Moon's motion across the sky can be measured in angular size: approximately 15° every hour, or 15″ per second.
Later, the Zij-i Ilkhani, compiled at the Maragheh observatory, sets the precession of the equinoxes at 51 arc seconds per annum, which is very close to the modern value of 50.2 arc seconds. [21] In the Middle Ages, Islamic and Latin Christian astronomers treated "trepidation" as a motion of the fixed stars to be added to precession.
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Looking at the arc of Moore’s career, there are indeed some popcorn hits. (Ghost made $505 million worldwide, and that’s in 1990 money.) But there are also more modest successes, some big ...
Polar motion in arc-seconds as function of time in days (0.1 arcsec ≈ 3 meters). [1] Polar motion of the Earth is the motion of the Earth's rotational axis relative to its crust. [2]: 1 This is measured with respect to a reference frame in which the solid Earth is fixed (a so-called Earth-centered, Earth-fixed or ECEF reference frame). This ...