You've seen rainbows. You've got excited about
double-rainbows. But prepare yourself, because meteorologists have
confirmed the existence of triple- and even
People have occasionally reported seeing triple rainbows, but
they're usually dismissed as hoaxes and only five scientific
reports have been made of them in the wild over the course of the
last 250 years.
Raymond Lee from the US Naval Academy studied these accounts of
triple rainbows and used a computer model to try and work out what
the best conditions are to make them observable. Dark thunderclouds
and a heavy downpour with uniformly-sized droplets are a necessity
-- in these conditions, if the sun breaks through the clouds, a
tertiary rainbow can be created that's visible -- Lee claims --
against the dark backdrop. He presented his findings to
the international conference on atmospheric optics, and challenged
attendees to find one.
Elmar Schmidt, from Germany's SRH University of Applied
Sciences, alerted some amateur storm photographers to the challenge
and they set out to get one on film. Michael Grossman eventually
succeeding in tracking one down after seeing a double rainbow in a
storm. When the rain got even stronger, he turned around and
snapped a picture of a tertiary rainbow in the sky -- capturing
photographic evidence of the phenomenon. "It is really
exaggerated to say that I saw it, but there seemed to be
something," he said. Michael Theusner also managed to capture an
image of what appears to be a quaternary rainbow.
Rainbows are created when sunlight enters a raindrop and is
separated out into its respective colours by refraction. Most of
that refracted light passes out the other side, but a small amount
is reflected, which is then concentrated (by the spherical shape of
the droplet) into a band at 138 degrees from the sun.
A double rainbow is formed when not all the reflected light
exits the drop, and is fed through the process again. It's dimmer
(because not as much light remains) but clearly visible, just
outside the primary rainbow, when the conditions are right.
Tertiary rainbows go through this process once more -- making them
dimmer again than the secondary rainbow, and on the opposite side
of the sky, which also happens to be the same side as the Sun's
glare. As such, they're extremely difficult to spot.
Thusner says, in the paper announcing
the discovery: "We report what is believed to be the first
photographic recording of a quaternary rainbow in nature. It
appears on the Sun side of the sky with its red arc at a radius of
about 45 degrees from the Sun. The original pictures have been
subjected to various forms of image processing to reveal the
tertiary rainbow as well as the quaternary rainbow, which are
separated by only a few degrees with their colors reversed and
their red arcs adjacent to each other."
Next time you're in a storm and a double-rainbow appears, turn
around and look towards the sun -- you might just see an
incredibly-rare third, or even fourth band of colour in the