4.Snoop Dogg posted this behind-the-scenes photo of himself and Britney Spears on the set of her music video for "Outrageous," in 2004:
5.Dolly Parton shared this photo of herself looking glam in the '80s:
6.Robert Downey Jr. wished Iron Man director and friend Jon Favreau a happy birthday by posting this behind-the-scenes photo of the two of them on set of the film in 2007:
7.In honor of his 34th birthday, Jeffrey Bowyer-Chapman posted this photo of himself in the early '90s:
8.Rob Lowe shared this photo of himself from the early '80s:
9.Christina Aguilera posted this photo from the Stripped album art, in celebration of the album's 16th anniversary:
10.Reese Witherspoon celebrated the 20th anniversary of Pleasantville, by posting this photo from the film of herself and co-star Tobey Maguire:
11.Ryan Reynolds celebrated his 42nd birthday by posting this photo of himself and his dad celebrating his bday in the '80s:
12.Mandy Moore was obviously in a fall mood and shared these photos from when she appeared on the cover of Seventeen magazine in 2000:
13.In honor of the 16th anniversary of her film, Frida, Salma Hayek posted this photo of herself dressed up as Frida Kahlo:
14.Mike Tyson shared this photo of himself and the late Tupac Shakur hanging out in the '90s:
15.Jamie Lee Curtis celebrated the success of her new movie, Halloween, by posting this photo of herself in the original 1978 Halloween:
16.Brie Larson shared this oh-so-'00s photo of herself:
17.And finally, Britney Spears celebrated the 20th anniversary of her debut single, "...Baby One More Time," by sharing a clip from the ICONIC music video, along with a very sweet caption: