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 AFV rear; the latter open outwards. In each side of the hull there are three firing ports with periscopes. On either side of the forward hull, a cluster of four 76 mm smoke grenade dischargers is mounted. The vehicle is fully amphibious, a folding trim board stowed at the front of the hull needs to be raised, and the vehicle can then propel itself in the water using its tracks. Standard equipment includes an NBC system, a Type 889 radio, and a Type 803 intercom system. Type 90 AFV The Type 90 is an armoured fighting vehicle produced by Chinese company