Hour angle

Time angle.

In astronomy, the hour angle is the arc of the equator counted from the point of intersection of the equator with the observer's meridian up to the hour circle of the star, in a clockwise direction, that of the apparent movement of the celestial vault. Although it could be measured in degrees, the hour is used for its measurement, a unit that is equivalent to 15º.

So, if an object has an hour angle of 2.5 hours, it transited the local meridian 2.5 hours ago, and is currently 37.5 degrees west of the meridian. Negative hour angles indicate the time remaining until the next transit through the local meridian. Of course, an hour angle of 0 means that the object is on the local meridian.

The following formula allows you to calculate the hour angle (HOR) using the Local Sidereal Time (TSL) of the place and the Right Ascension (AR) of the object:

The hour angle of the Sun (ω) indicates the angular displacement of the Sun on the plane of the solar trajectory. Solar noon is taken as the origin of the angle and increasing values in the direction of the movement of the Sun. Each hour corresponds to 15° (360°/24 hours).

Knowing the solar time and knowing that the origin of coordinates is in the local meridian and that one solar hour corresponds to 15°

ω ω =(horrasorlar− − 12)↓ ↓ 15 {displaystyle omega ={(hour solar-12)}*{15^{circ}}}}

Negative value angles indicate that the Sun has not yet reached the local meridian.

The angles with positive value indicate that the Sun already passed through the local meridian.