Editing Hour angle (section)

==Relation with right ascension==
[[File:Hour angle still1.png|thumb|right|300px|As seen from above the [[Earth]]'s [[geographic pole|north pole]], a star's local hour angle (LHA) for an observer near New York (red dot). Also depicted are the star's [[right ascension]] and Greenwich hour angle (GHA), the [[Sidereal time|local mean sidereal time]] (LMST) and [[Sidereal time|Greenwich mean sidereal time]] (GMST). The symbol ʏ identifies the [[March equinox]] direction.<br>Assuming in this example the day of the year is the March equinox so the sun lies in the direction of the grey arrow then this star will rise about midnight. Just after the observer reaches the green arrow dawn comes and overwhelms with light the visibility of the star about six hours before it sets on the western horizon. The Right Ascension of the star is about 18<sup>h</sup>]]

The local hour angle (LHA) of an object in the observer's sky is
<math display=>\text{LHA}_{\text{object}} = {\text{LST}} - \alpha_{\text{object}}</math>
or
<math display=>\text{LHA}_{\text{object}} = {\text{GST}} + \lambda_{\text{observer}} - \alpha_{\text{object}}</math>
where LHA<sub>object</sub> is the local hour angle of the object, LST is the [[Sidereal time|local sidereal time]], <math>\alpha_{\text{object}}</math> is the object's [[right ascension]], GST is [[Sidereal time|Greenwich sidereal time]] and <math>\lambda_{\text{observer}}</math> is the observer's [[longitude]] (positive east from the [[prime meridian]]).<ref>{{cite book  | last = Meeus | first = Jean | title = Astronomical Algorithms | publisher = Bell, Inc., Richmond, VA | date = 1991 | page = 88 | ISBN = 0-943396-35-2 }}</ref> These angles can be measured in time (24 hours to a circle) or in degrees (360 degrees to a circle)—one or the other, not both.

Negative hour angles (−180° < LHA<sub>object</sub> < 0°) indicate the object is approaching the meridian, positive hour angles (0° < LHA<sub>object</sub> < 180°) indicate the object is moving away from the meridian; an hour angle of zero means the object is on the meridian.

Right ascension is frequently given in sexagesimal hours-minutes-seconds format (HH:MM:SS) in astronomy, though may be given in decimal hours, sexagesimal degrees (DDD:MM:SS), or, decimal degrees.