28 November 2022

Supernumerary rainbows and airglow ripples

"Supernumerary rainbows only form when falling water droplets are all nearly the same size and typically less than a millimeter across. Then, sunlight will not only reflect from inside the raindrops, but interfere, a wave phenomenon similar to ripples on a pond when a stone is thrown in. In fact, supernumerary rainbows can only be explained with waves, and their noted existence in the early 1800s was considered early evidence of light's wave nature."
Not to be confused with airglow ripples:

"The unusual pattern is created by atmospheric gravity waves, waves of alternating air pressure that can grow with height as the air thins, in this case about 90-kilometers up. Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence, the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark."


  1. Wow, that has got to be the largest number of supernumerary bows I've ever seen. Also interesting to note is how their distance to the main bow isn't constant: they are packed closer together near the bottom and further apart as you go up. If I understand this graphic correctly, that means the size of the water droplets near the ground than was larger than those higher up in the air. What is more, the supernumerary closest to the main bow gradually creates a gap large enough for a new supernumerary to appear about 2/3 up. Quite an exceptional picture.

  2. I don't think the photo is showing super numerary rainbows. In my experience those usually lack reds and yellows and are more parallel

    1. You might drop a note to NASA, who are responsible for the Astronomy Photo of the Day series. I am sure they would appreciate being informed of any errors they have made.

  3. Caption on the first picture...
    Then she dropped the towel.

    I'll see myself out... xoxoxoBruce


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