"This lake remained clear for a long time. At one point I saw this white bow with the waning gibbous behind me. I had no clue what it was that I saw and started to take pictures," Kast wrote SPACE.com in an email.
Similar to a rainbow, tiny water droplets that cause fog reflect light. Lunar fog bows typically appear white because sunlight reflected from the moon is weak. Some photographers have also captured so-called "moonbows," which are similar to rainbows in that they do include colors.
The lunar fog bows lack of colors is caused by the smaller water drops … so small that the wavelength of light becomes important. Diffraction smears out colors that would be created by larger water drops in rainbows, according to NASA.