It doesn't just occur in clouds; it can appear in clear air, in the ocean, and even in the atmosphere ... fluctus clouds are more likely to appear around sunrise or sunset, which is when lower ...

The iridescent cloud reveals new clues about ice formation in the Martian atmosphere (no little green men, sorry).

Readers’ photos celebrate sunrises and sunsets, when the light is the most pleasing. Fifty-one photos were sent in; here are ...

The world below disappears, swallowed by an ocean of clouds stretching as far as the ... paths in darkness and arriving at Kem Baha before sunrise. The return trek on the same day is equally ...