Earth, Wind and Fire: What is the significance of September 21?

Released over 40-years ago in 1978, the tune was the group's most popular song, so much so that it is still a hit today. 

One of lines in the opening bars of the song is "Do you remember the 21st night of September", which has left fans wondering why this date in particular was chosen. 

Here's what we know about Earth, Wind and Fire's September date...

What is the significance of September 21 in Earth, Wind and Fire's song?

Although the exact significance of September 21 in the song September has never been revealed, there are some suggestions.

Songwriter Allee Willis, who worked with the group to write the hit, explained their reasoning for selecting that specific date. 

Speaking in an interview in 2008, she said: "We went through all the dates: 'Do you remember the first, the second, the third, the fourth ... ' and the one that just felt the best was the 21st."

Unfortunately for fans, she did not divulge any anecdotes about the significance of this date: "I constantly have people coming up to me and they get so excited to know what the significance was.

"And there is no significance beyond it just sang better than any of the other dates. So ... sorry!"

What are the lyrics to September? 

Do you remember, the 21st night of September?
Love was changing the mind of pretenders
While chasing the clouds away
Our hearts were ringing
In the key that our souls were singing
As we danced in the night
Remember
How the stars stole the night away, oh yeah

Hey, hey, hey
Ba-dee-ya, say, do you remember?
Ba-dee-ya, dancing in September
Ba-dee-ya, never was a cloudy day

Ba-du, ba-du, ba-du, ba-du

Ba-du, ba-du, ba-du, ba-du
Ba-du, ba-du, ba-du-da, yeah

My thoughts are with you

Holding hands with your heart to see you
Only blue talk and love
Remember
How we knew love was here to stay
Now December
Found the love we shared in September
Only blue talk and love
Remember
True love we share today

Hey, hey, hey
Ba-dee-ya, say, do you remember?
Ba-dee-ya, dancing in September
Ba-dee-ya, never was a cloudy day
There was a
Ba-dee-ya, say, do you remember?
Ba-dee-ya, dancing in September
Ba-dee-ya, golden dreams were shiny days

The bell was ringing, oh, oh
Our souls was singing
Do you remember, never a cloudy day, yow

There was a
Ba-dee-ya, say, do you remember?
Ba-dee-ya, dancing in September
Ba-dee-ya, never was a cloudy day
There was a

Ba-dee-ya, say, do you remember?
Ba-dee-ya, dancing in September
Ba-dee-ya, golden dreams were shiny days

Ba-dee-ya, dee-ya, dee-ya
Ba-dee-ya, dee-ya, dee-ya
Ba-dee-ya, dee-ya, dee-ya, dee-ya
Ba-dee-ya, dee-ya, dee-ya
Ba-dee-ya, dee-ya, dee-ya
Ba-dee-ya, dee-ya, dee-ya, dee-ya