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A second of arc, arcsecond (arcsec), or arc second, denoted by the symbol ″, [2] is 1 / 60 of an arcminute, 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.
An arcsecond is 1/3600th of one degree (1°) and a radian is 180/π degrees. So one radian equals 3,600 × 180/ arcseconds, which is about 206,265 arcseconds (1 rad ≈ 206,264.806247"). Therefore, the angular diameter of an object with physical diameter d at a distance D, expressed in arcseconds, is given by: [9]
{{Deg2DMS |positive decimal degrees| p =precision| sup =ms}} |p= is optional and defaults to 3. It is the number of decimal digits that the seconds are rounded to. |sup= is optional and changes the default apostrophe-format for arcminutes and arcseconds (1° 2′ 3″) to the m-s-format for arcminutes and arcseconds (1° 2 m 3 s).
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 ]
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol ′, is a unit of angular measurement equal to 1 / 60 of one degree. [1] Since one degree is 1 / 360 of a turn, or complete rotation, one arcminute is 1 / 21 600 of a turn.
Solid angles can also be measured in square degrees (1 sr = (180/ π) 2 square degrees), in square arc-minutes and square arc-seconds, or in fractions of the sphere (1 sr = 1 / 4 π fractional area), also known as spat (1 sp = 4 π sr). In spherical coordinates there is a formula for the differential,
The angular diameter distance reaches a maximum at a redshift = (in the ΛCDM model, this occurs at ), such that the slope of () changes sign at =, or > <, < >.In reference to its appearance when plotted, is sometimes referred to as the turnover point.
Since a complete circle contains 24 h of right ascension or 360° (degrees of arc), 1 / 24 of a circle is measured as 1 h of right ascension, or 15°; 1 / 1440 of a circle is measured as 1 m of right ascension, or 15 minutes of arc (also written as 15′); and 1 / 86400 of a circle contains 1 s of right ascension, or 15 ...