Sol is another word for the Sun, borrowed from Latin. Scientists sometimes use Sol (with a capital S) when discussing the Sun as a specific star rather than just “that bright thing in the sky.” For example, astronomers might compare our Sol to other stars to understand how typical or unusual it is.

The word appears most often in science fiction and space exploration. When scientists track time on Mars, they call a Martian day a sol because Mars rotates slightly slower than Earth: one sol equals about 24 hours and 39 minutes. NASA mission controllers monitoring rovers on Mars don't say “On day 47...” but rather “On sol 47...” This helps avoid confusion between Earth days and Mars days.

You might also encounter Sol in the phrase Sol system, another way of saying solar system.

In music, sol (also spelled so) is the fifth note in the do-re-mi scale. When Julie Andrews sang “Sew, a needle pulling thread” in The Sound of Music, she was teaching the von Trapp children to sing so, which represents the note sol in the song.