Next time you fly, ask for a window seat so you can watch for these optical atmospheric effects described by Les Cowley, atmospheric optics expert.

On the side of the plane opposite the sun, you may be able to spot a glory, or bright white glow surrounded by one or more shimmering rings of color. This can be seen only if there are clouds beneath the plane, since the glory surrounds the shadow of the plane within the clouds.

'These rings are formed when light is scattered backwards by individual water droplets in the cloud,' says Cowley.

A second phenomenon visible from that side of the airplane is called an opposition effect, which is a bright patch of light moving along the ground below you. This spot is the point where the shadow of the plane is hidden beneath the plane itself, so the area looks brighter than its surroundings.

On the sunward side of the plane, ice halos and sub horizon halos are visible. Ice halos 'are rings and arcs of light caused by ice crystals in high clouds ... often rainbow-colored' Cowley says.

Sub horizon halos are bright lights that are a direct reflection of the sun from millions of flat ice crystals floating in the clouds.

If you happen to be flying during sunrise or sunset, make sure to watch. Cowley says 'the speed of the aircraft can make them faster or slower than usual.'

For pictures of these sights, visit Cowley's Web site Atmospheric Optics.