In astronomy and celestial navigation, the hour angle is one of the coordinates used in the equatorial coordinate system to give the direction of a point on the celestial sphere. The hour angle of a point is the angle between two planes: one containing the Earth's axis and the zenith (the meridian plane), and the other containing the Earth's axis and the given point (the hour circle passing through the point).

The angle may be expressed as negative east of the meridian plane and positive west of the meridian plane, or as positive westward from 0° to 360°. The angle may be measured in degrees or in time, with 24^h = 360° exactly.

In astronomy, hour angle is defined as the angular distance on the celestial sphere measured westward along the celestial equator from the meridian to the hour circle passing through a point. It may be given in degrees, time, or rotations depending on the application. In celestial navigation, the convention is to measure in degrees westward from the prime meridian (Greenwich hour angle, GHA), the local meridian (local hour angle, LHA) or the first point of Aries (sidereal hour angle, SHA).

M. Ali Manikfan (where "M." stands for Muraiduganduar, also known as Muräduganduar Ali Befanu;manikfan and befanu are actually titles) (born 16 March 1938, Minicoy Island, Lakshadweep) is an Indian marine researcher, ecologist, shipbuilder, and a polyglot. He is noted for his autodidactic research skills in the marine, ecology, and agricultural fields, not holding any formal educational qualification, and for promoting a life of simplicity.

Ali Manikfan was born to Musa Manikfan and Fatima Manika in Minicoy Island of Lakshadweep on 16 March 1938. His father Musa sent him to Kannur for formal education. As he was not interested in formal education, he left his studies and returned to his home land. According to him formal education is artificial and pointless and best way to acquire knowledge is getting wisdom by observing our environment. Ali Manikfan knows a great number of languages. Besides his mother tongue Divehi (Mahl), he learned English, Hindi and Malayalam, Arabic, Latin, French, Russian, German, Sinhalese, Persian, Sanskrit, Tamil and Urdu. His other areas of interest are marine biology, marine research, geography, astronomy, social science, traditional shipbuilding, education, fisheries, agriculture and horticulture. In 1956 he worked as a teacher and then became a clerk in Minicoy. (Indian government's chief civil official on the Island). But his interest was in marine life. In 1960s he joined the Central Marine Fisheries Research Institute of India.