Hour angle The angle may be measured in degrees or in time, with 24 = 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), from the local meridian (local hour angle, LHA) or from the first point of Aries (sidereal hour angle, SHA). The hour angle
61 cm Type 90 torpedo 61 cm Type 90 torpedo The 61 cm Type 90 torpedo was a surface-fired torpedo used by the Imperial Japanese Navy during World War II. It was used in the s and in most cruisers, including the , , , and heavy cruisers after refits during the 1930s. It was superseded by the Type 93 oxygen-powered torpedo, commonly called the "Long Lance", as oxygen generating equipment was installed aboard the cruisers. The torpedo was based on a newly developed British Whitehead torpedo. This weapon used a new double-action two-cylinder engine rather than the four-cylinder radial engine used by World War