Soon, it will be the 21st night of September.
Here's the story behind the song, as told in 2014 by NPR:
Allee Willis was a struggling songwriter in LA — until the night she got a call from Maurice White, the leader of Earth, Wind & Fire. White offered her the chance of a lifetime: to co-write the band's next album. Willis arrived at the studio the next day hoping it wasn't some kind of cosmic joke.
"As I open the door, they had just written the intro to 'September.' And I just thought, 'Dear God, let this be what they want me to write!' Cause it was obviously the happiest-sounding song in the world," Willis says.
Using a progression composed by Earth, Wind & Fire guitarist Al McKay, White and Willis wrote the song over the course of a month, conjuring images of clear skies and dancing under the stars. Willis says she likes songs that tell stories, and that at a certain point, she feared the lyrics to "September" were starting to sound simplistic. One nonsense phrase bugged her in particular.
"The, kind of, go-to phrase that Maurice used in every song he wrote was 'ba-dee-ya,' " she says. "So right from the beginning he was singing, 'Ba-dee-ya, say, do you remember / Ba-dee-ya, dancing in September.' And I said, 'We are going to change 'ba-dee-ya' to real words, right?' "