What caused Sydney’s double rainbow?

THE double rainbow over Sydney delighted millions of people yesterday who flooded social media with their snaps. But how many saw the hidden surprise?

SYDNEY, AUSTRALIA - JUNE 17: A rainbow is seen over the Sydney Harbour Bridge on June 17, 2015 in Sydney, Australia. (Photo by Cameron Spencer/Getty Images)

A DOUBLE rainbow thrilled Sydneysiders yesterday who took to their social media accounts to share pictures of the rare event — but many may have missed a secret hidden within the rainbows themselves.

Anthony Duke, a meteorologist at Weatherzone, said the second rainbow, which was the weaker one, was actually a mirror image of the first.

“The second rainbow is actually a reverse like a mirror image. It might have red on the outside of the arc, but on the second the red will be on the inside.”

Mr Duke said the second rainbow was a lot weaker than the first.

Double rainbows are rare, experts say, and the second one is a mirror image of the first.

“It takes a bit of different angle which is why it appears outside of the first, so it appears weaker because it has to go through more of the raindrop.”

The initial rainbow was caused through the light bouncing through the raindrop once. The double occurred when the light bounced through twice, off the back of the droplet.

And with that, a second rainbow is born.

“You need a little bit more light to see them, and generally when it’s raining there’s not huge amount of light available, so only on these rare occasions we you have consistent rain but at the same time enough light to form another rainbow.”