Prominent absorption bands of methane occur at wavelengths above 600 nm, in the red and infrared portion of the spectrum. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue,[50] although Neptune's vivid azure differs from Uranus's milder cyan. Since Neptune's atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune's colour.[15]
Neptune's atmosphere is sub-divided into two main regions; the lower troposphere, where temperature decreases with altitude, and the stratosphere, where temperature increases with altitude. The boundary between the two, the tropopause, occurs at a pressure of 0.1 bars (10 kPa).[13] The stratosphere then gives way to the thermosphere at a pressure lower than 10−5 to 10−4 microbars (1 to 10 Pa).[13] The thermosphere gradually transitions to the