Local hour angle

The local hour angle (eng: Local Hour Angle, LHA) is the hour angle of the vernal equinox on the location of the observer. It can be calculated from the Greenwich hour angle (Grt), which is published every year in the Nautical Yearbook . The term is only used in navigation , while in geodesy and astronomy it is called local sidereal time .

The LHA is obtained by adding the length λ of the observation site and the Grt. Eastern longitudes have a positive sign , western longitudes a negative one.

In addition to the declination (δ), the local hour angle is required in astronomical navigation using the HO 249 tables as an argument for calculating the altitude and azimuth in the horizontal coordinate system.

See also:

• astronomical navigation
• spherical astronomy