Solar zenith angle minutes of arc, which is less than the apparent angular radius of the sun. The formula also neglects the effect of atmospheric refraction. Sunset and sunrise occur (approximately) when the zenith angle is 90°, where the hour angle "h" satisfies Precise times of sunset and sunrise occur when the upper limb of the Sun appears, as refracted by the atmosphere, to be on the horizon. A weighted daily average zenith angle, used in computing the local albedo of the Earth, is given by where "Q" is the instantaneous insolation. For example, the solar elevation angle is : An exact calculation
Type 90 Kyū-maru procurement plan was established in the 1980s while Japan was experiencing asset price bubble. After the asset price bubble burst in 1991 and the collapse of Soviet Union in 1992, Japan started to cut its defence budget. In order to save budget for Kongo Class missile destroyers and other new weapons, Japan made a plan to reduce the size of its tank force. The production of Type 90 therefore slowed down and part of its budget was shifted to the research and development of the new Type 10 main battle tank. Being 12 tonnes heavier than its predecessor Type 74