The four rainbows that took the Internet by storm appeared over New York train station yesterday morning.
Commuter Amanda Curtis took the Internet flare by posting a photograph of four rainbows shining in the sky above Glen Cove train station on New York’s Long Island. Though some on social media expressed skepticism about the phenomenon, experts agree that getting four rainbows at once in close proximity is entirely possible.
Beautiful, yes. A quadruple rainbow? Not exactly.
According to Raymond Lee, a research professor at the U.S. Naval Academy, what we’re really looking here are “sunlight-reflection” rainbows.
These rainbows can form when sunlight is reflected from a water surface behind or in front of the viewer, with the result that the sun’s reflected virtual image forms a second light source which appears as far below the horizon as the sun’s real image is above it. A map of the Glen Cove, NY LIRR station shows that Curtis had a great location with Hempstead Bay to the [northwest], nearly opposite the morning sun.”
Lee, who studied about rainbows extensively, verified the first legit quadruple rainbow back in 2011. And as you can see, it looks nothing like Curtis’s photo:
What you’re really seeing is two offset double rainbows. The two brighter ones are the primary and secondary rainbows. The fainter pair that appears higher in the sky is the result of sunlight reflected off of a body of water behind the photographer. A quick search shows two bays that could have done the trick—Oyster Bay or Hempstead Bay,” the meteorologist explains.
Since a rainbow forms when sunlight enters raindrops in the atmosphere and is reflected back out. A double rainbow occurs when sunlight left over from that initial reflection comes back through the raindrops a second time.
In the case of the two double rainbows, they are different than true quaternary rainbows, which are incredibly rare. That there have only been 4 or 5 scientifically documented sightings of quaternary or tertiary rainbows since 1700, according to Lee.
A quaternary rainbow forms when sunlight enters and reflects out of raindrops four times. With each pass through the raindrops, the amount of light is reduced, making tertiary and quaternary rainbows incredibly dim.
Conditions have to be just right for them to form—heavy rain in addition to direct sunlight.
The optical deck is heavily stacked against our ever seeing the higher-order tertiary and quaternary bows.”
via National Geographic