Editing Astronomical coordinate systems (section)

=== Notes on conversion ===

* Angles in the degrees ( ° ), minutes ( ′ ), and seconds ( ″ ) of [[Minute of arc|sexagesimal measure]] must be converted to decimal before calculations are performed. Whether they are converted to decimal [[Degree (angle)|degrees]] or [[radian]]s depends upon the particular calculating machine or program. Negative angles must be carefully handled; {{nowrap|−10° 20′ 30″}} must be converted as {{nowrap|−10° −20′ −30″}}.
* Angles in the hours ( <sup>h</sup> ), minutes ( <sup>m</sup> ), and seconds ( <sup>s</sup> ) of time measure must be converted to decimal [[Degree (angle)|degrees]] or [[radian]]s before calculations are performed. 1<sup>h</sup>&nbsp;=&nbsp;15°; 1<sup>m</sup>&nbsp;=&nbsp;15′; 1<sup>s</sup>&nbsp;=&nbsp;15″
* Angles greater than 360° (2{{pi}}) or less than 0° may need to be reduced to the range 0°–360° (0–2{{pi}}) depending upon the particular calculating machine or program.
* The cosine of a latitude (declination, ecliptic and Galactic latitude, and altitude) are never negative by definition, since the latitude varies between −90° and +90°.
* [[Inverse trigonometric functions]] arcsine, arccosine and arctangent are [[quadrant (plane geometry)|quadrant]]-ambiguous, and results should be carefully evaluated. Use of  the [[Atan2|second arctangent function]] (denoted in computing as {{mono|atn2(''y'',''x'')}} or {{mono|atan2(''y'',''x'')}}, which calculates the arctangent of {{math|{{sfrac|''y''|''x''}}}} using the sign of both arguments to determine the right quadrant) is recommended when calculating longitude/right ascension/azimuth. An equation which finds the [[Trigonometric functions|sine]], followed by the [[Inverse trigonometric functions|arcsin function]], is recommended when calculating latitude/declination/altitude.
* Azimuth ({{math|''A''}}) is referred here to the south point of the [[horizon]], the common astronomical reckoning. An object on the [[Meridian (astronomy)|meridian]] to the south of the observer has {{math|''A''}} = {{math|''h''}} = 0° with this usage. However, n [[Astropy]]'s AltAz, in the [[Large Binocular Telescope]] FITS file convention, in [[XEphem]], in the [[International Astronomical Union|IAU]] library [[SOFA (astronomy)|Standards of Fundamental Astronomy]] and Section B of the [[Astronomical Almanac]] for example, the azimuth is East of North.  In [[navigation]] and some other disciplines, azimuth is figured from the north.
* The equations for altitude ({{math|''a''}}) do not account for [[atmospheric refraction]].
* The equations for horizontal coordinates do not account for [[diurnal parallax]], that is, the small offset in the position of a celestial object caused by the position of the observer on the [[Earth]]'s surface. This effect is significant for the [[Moon]], less so for the [[planet]]s, minute for [[star]]s or more distant objects.
* Observer's longitude ({{math|''λ''<sub>o</sub>}}) here is measured positively eastward from the [[prime meridian]], accordingly to current [[International Astronomical Union|IAU]] standards.