Happy “rainbow season”!
This time of the year, when we see consistent rounds of early evening showers and thunderstorms, we often see rainbows when the sun starts to descend lower on the horizon. Rainbows occur when sunlight passes through rain droplets at a 48° angle- which happens more often for our area this time of the year when the sun is lower on the horizon and we have afternoon storms firing up.
Even better, thanks the typical position of our afternoon storms, the angle of the sun during the time we typically see storms, and our flat elevation—we are prone to seeing double rainbows. Double rainbows are also more likely within heavy rainfall, which is also typical for us this time of the year.
According to NOAA, a secondary rainbow, or double rainbow, appears if the sunlight is reflected twice inside the water droplets. Secondary rainbows are fainter, and the order of the color is reversed, with red on the bottom.
Sometimes you can see another, fainter secondary rainbow above the primary rainbow. The primary rainbow is caused from one reflection inside the water droplet. The secondary rainbow is caused by a second reflection inside the droplet, and this “re-reflected” light exits the drop at a different angle (50-53° instead of 42° for the red primary bow). This is why the secondary rainbow appears above the primary rainbow.
The NWS defines a rainbow as follows: A luminous arc featuring all colors of the visible light spectrum (red, orange, yellow, green, blue, indigo, and violet). It is created by refraction, total reflection, and the dispersion of light. It is visible when the sun is shining through air containing water spray or raindrops, which occurs during or immediately after a rain shower. The bow is always observed in the opposite side of the sky from the sun.
You are more likely to see a rainbow a few hours after sunrise or a few hours before sunset. As the sun is lower on the horizon, it creates the opportunity for the rays of light to pass through water, like an afternoon shower. As the rays of light pass through the water, the light is refracted. Refraction is when light (or radio waves) passes through a medium (like water) and it changes the speed at which that light is traveling. When the water slows the light down, it spreads out the spectrum of colors, resulting in a rainbow.
According to NOAA, Light enters a water droplet, bending as it slows down a bit going from air to denser water. The light reflects off the inside of the droplet, separating into its component wavelengths—or colors. When it exits the droplet, it makes a rainbow.
NOAA further explains the colors of the rainbow: sunlight is made up of many wavelengths—or colors—of light. Some of those wavelengths get bent more than others when the light enters the water droplet. Violet (the shortest wavelength of visible light) bends the most, red (the longest wavelength of visible light) bends the least. So when the light exits the water droplet, it is separated into all its wavelengths. The light reflecting back to you, the observer with the Sunlight coming from behind you, from the water droplets will appear separated into all the colors of the rainbow! Violet will be on the bottom and red on the top.
The rainbow will always form on the opposite side of the sky from the sun, and you must be on the opposite side of the rain from the sun to see it. If the sun is setting to our west, and it is raining along I-75, you would see the rainbow when looking east.
During the middle of the day, its difficult to get rainbows because the light spectrum that is spread out as the suns rays travel through showers, is moving towards the ground, and we wouldn’t be able to see it.