The brightest and best-defined rainbows come from sunlight striking large, uniform droplets. Showery weather and plenty of daylight make June a prime month for rainbow spotting. Rather than a single arc, you may be lucky enough to spot multiple rainbows if you know where to look.
The most common multiple form is a double rainbow. Most rainbows are produced by internal reflection within raindrops. When the light is strong enough for a double internal reflection, you may see a dimmer secondary rainbow around the main bow, with the order of the colours reversed.
Look closer and you may see faint supernumerary arcs just inside the main rainbow. These are paler and may show only as pink, blue and purple bands. They were explained by Thomas Young in 1804 as the result of a complex interference effect, and again they are only visible with bright rainbows.
You usually see rainbows opposite to the sun; from your point of view, the rainbow is centred on the shadow of your head. Very rarely though, faint additional rainbows may appear in the other direction, close to the sun. These are known as tertiary and quaternary rainbows. These are very much dimmer, and there have only ever been a handful of scientifically-accepted sightings of such rainbows.
