The rainbow — light and physics in perfect harmony

How does a rainbow form?

A rainbow forms when sunlight hits water droplets in the air and is refracted, reflected and dispersed into different colours. Light is refracted (bent) as it enters the droplet, reflected off the inside surface, and refracted again as it exits. Different wavelengths (colours) bend at slightly different angles, separating white light into the rainbow's seven colours: red, orange, yellow, green, blue, indigo and violet.

The angle is everything

A rainbow always appears at a 42-degree angle from the direction opposite the sun. This means the sun is always behind you when you see a rainbow. The centre of the rainbow (the antisolar point) lies directly in the shadow of your head. That is why you never see a complete circle from the ground — but from an aircraft you can see a full rainbow ring!

Double rainbow

Sometimes you see a double rainbow. The outer arc is formed by light that reflects twice inside the droplet, and the colour sequence is reversed — red on the inside, violet on the outside. The area between the two arcs, known as Alexander's dark band, is noticeably darker than the surrounding sky.

Rainbows in western Norway

Western Norway is one of the best places in Europe for rainbow observations. The high rainfall combined with frequent sunny breaks between clouds creates ideal conditions. Especially in autumn, when low-pressure systems and sunbeams alternate rapidly, you can see rainbows almost daily from Kvisvik. The fjords also produce reflected rainbows in the water — a double spectacle.

The moonbow

During a full moon and heavy rainfall, you may occasionally see a moonbow — a rainbow lit by moonlight instead of sunlight. It appears almost white to the naked eye but reveals colours in long-exposure photographs. A rare and magical phenomenon.