It's the 21st of September. Happy Earth, Wind & Fire Day!

Social media is exploding today with GIFs of Earth, Wind & Fire’s Maurice White, decked in a striped shirt and surrounded by a feedback tunnel of psychedelic light, joyfully bellowing, Ba-dee-ya!

It must be the 21st of September.

Today is Earth, Wind & Fire Day, an unofficial holiday, but one that’s widely celebrated as fans of the R&B band honor the first line of the earworm “September.” (Today’s date is prominently mentioned in the song’s opening line.)

It’s a song that has played at both the Democratic and Republican conventions (in the same year!). It has been featured in at least 14 major motion pictures and numerous TV shows. And it’s a song that still has people wondering exactly what “ba-dee-ya” means. (Spoiler: No one has figured it out in the 43 years the song has been around.)

A goofy thing to celebrate? Maybe, but it’s a capsule of pure joy.

Prince, famously, instructed his personal DJ to end every set with the song. And in a world that has gotten a lot harder in recent years, people are responding to it more than ever. Two years ago, streams of “September” were up 225% on Spotify, with more than 2.5 million listens to the song.

Each year, meanwhile, the online world anxiously awaits comedian Demi Adejuyigbe’s…unique…celebration of the song on YouTube. While he had planned to stop last year, after delivering a tribute for five years in a row, he promised at the end of 2020’s performance (which got 1.9 million views) to make another version this year if fans donated $50,000 to various charities. They donated over $332,000.

So what is it that makes “September” such an earworm? Music theory experts say it’s that opening line, which makes anyone who hears it experience a yearning feeling and supply their own memories. And the song’s structure is tailor-made to keep you dancing.

As for the significance of the date? There really isn’t one.

“I constantly have people coming up to me, and they get so excited to know what the significance was,” said cowriter Allee Willis. “And there is no significance beyond it just sang better than any of the other dates. So…sorry!”