Q&A: General Astronomy and Space Science
Why does the star Sirius sometimes appear to change colors
rapidly, red-green-white, several times per second?
The Earth's atmosphere acts like a prism to split (refract)
the light from bright stars into the various colors of the
rainbow (spectrum). Different colors of light are bent by
different amounts, so as turbulent eddies in the atmosphere
move through your line of sight to the star, you many seen
more red, yellow, green or blue light, depending on the
properties of the atmosphere. This light show is most
noticeable when the star is near the horizon, so you are
looking through more of the Earth's atmosphere, or when there
is a lot of turbulence or smog in the atmosphere, and
sometimes leads to reports of UFOs.