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 Type 90 AFV The Type 90 is an armoured fighting vehicle produced by Chinese company Norinco; it is the successor for the Type 85 AFV of which it uses some components. The Type 90 series was developed for export, and consists of at least 10 different types; its industrial index is YW535. This new type is rather similar to its predecessors Type 85 AFV and Type 89 AFV, but the hull has a different shape, having a vertical lower side wall and a sloping upper side wall. Overall, the Type 90 is bigger and heavier, yet has a lower profile.