Right angle Right angle In geometry and trigonometry, a right angle is an angle of exactly 90° (degrees), corresponding to a quarter turn. If a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles. The term is a calque of Latin "angulus rectus"; here "rectus" means "upright", referring to the vertical perpendicular to a horizontal base line. Closely related and important geometrical concepts are perpendicular lines, meaning lines that form right angles at their point of intersection, and orthogonality, which is the property of forming right angles, usually applied
Hour angle is paired with the declination to fully specify the location of a point on the celestial sphere in the equatorial coordinate system. The local hour angle (LHA) of an object in the observer's sky is where LHA is the local hour angle of the object, LST is the local sidereal time, formula_3 is the object's right ascension, GST is Greenwich sidereal time and formula_4 is the observer's longitude (positive east from the prime meridian). 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.