Sunset or sundown is the daily disappearance of the Sun below the horizon as a result of Earth’s rotation. The Sun will set exactly due west at the equator on the spring and fall equinoxes, each of which occurs only once a year. Lenticular clouds are stationary clouds that form in the troposphere, typically in perpendicular alignment to the wind direction. They are often comparable in appearance to a lens or saucer. 4K UHD 3840×2160.