1. Jessica Simpson shared this photo of when she did a shoot for Allure magazine in 2006.
2. Iman posted these photos of when she and Madonna attended an AIDS benefit for New York's St. Vincent’s Hospital in 1986.
3. Dan Levy shared this cute photo of himself from the mid-'80s.
4. Joseph Gordon-Levitt kept the cute theme going and posted this photo of him and his cat in the early '90s.
5. Rashida Jones shared this photo she and her friends took at the mall in the early '90s.
6. In honor of her friend and Buffy co-star Seth Green's birthday, Sarah Michelle Gellar posted this childhood photo of the two of them in the early '80s.
7. Mark Ruffalo posted this photo of himself taken in the early '90s, when he was a struggling actor in LA.
8. Paul McCartney shared this photo his late wife, Linda McCartney, took of him in the bath in 1969.
9. U2 celebrated the 21st anniversary of their album Pop by posting a clip from the lead single, "Discothèque."
10. Barbra Streisand posted this photo from the ’60s of herself in the kitchen of her first home alongside her beloved dog, Sadie.
11. Will Smith shared this clip of himself talking about his memories of the first time hanging out with the legendary group Run-DMC.
12. And finally, Kelsey Grammer shared this touching tribute to his Frasier co-star, John Mahoney, who died earlier this week.
He was my father. I loved him.