A rainbow appears in the part of the sky directly opposite the sun.

The longer version

Because the light is bent back toward its source, a rainbow only shows when you face away from the sun with the rain in front of you. The centre of the arc lies at the point directly opposite the sun from your viewpoint, which is known as the antisolar point.

This geometry explains why bows appear toward the west in the morning and toward the east in the afternoon, and why they are absent at midsummer midday when the sun sits high. Seen from an aircraft, the same arrangement can close into a full circle.

Where this entry sits

Clouds, wind, rain, and storms shape daily life in ways that most people barely notice. This collection explains snow, lightning, rainbows, the turning seasons, temperature, the instruments forecasters rely on, and scraps of old weather lore. The full list sits on the Weather and Climate page, where every entry is listed in order.