Night sky

Just after the sun is gone below the horizon, the sky keeps lit during a few moments. During that period of time, the sky appears mainly blue and is known as twilight. This is due to ozone and is taken into account in our model.

Sky after the sun went below the horizon. Note the blue shift due to ozone absorption.

During the night, sun has gone far under the horizon. The only potential source of visible direct light is the moon (reflecting the light it receives from the sun hidden to the observer). Even during the day, the moon can be visible.

The moon can be seen both during the night or the day (depending on the relative position of earth, sun and moon).

Other major components of the night sky are the stars. Note that the stars are only visible under clear sky, with no moon and after some eye adaptation. In our model this means that you need to remove the moon from the viewing pyramid, try to keep the sky turbidity low and increase the exposure of the tone mapping operator used. Stars are several times of magnitude darker than the sun or the moon and you may need to multiply the day exposure by around 10000-100000 to get a correct night exposure with stars.

Night sky using an exposure of 0.1 (on the left) compared to the same sky with an exposure of 5000 (on the right): the stars become visible.