1. Chris Evans celebrated #NationalPetDay by sharing these photos of himself with his first doggie friend, East:
For #NationalPetDay I thought I would give a little love to my first pet. I always said that as soon as I had my own place, the first thing on the list would be to get a dog. East was that dog. We had 12 good years. He was a champ.
2. Kacey Musgraves posted this photo of herself rocking a flower crown in the early '90s:
🌼🌸 #FBF 🌸🌼
3. Will Smith jumped on the "Old Town" bandwagon and posted this clip from his 1999 music video for "Wild Wild West" set to the Lil Nas X hit:
4. Julia Roberts shared this photo of herself as a kid in celebration and shock that her friend, Paul Rudd, is 50 ('cause seriously he looks 33):
5. Zooey Deschanel posted this behind-the-scenes photo of herself and Joseph Gordon-Levitt on the set of 500 Days of Summer, in 2008:
6. The Spice Girls shared this classic photo of themselves from 1997:
7. Nicole Kidman posted these photos taken by the late Herb Ritts in the early '00s:
8. Michelle Pfeiffer also paid tribute to Herb Ritts and posted these photos he took of her in 1992, for Rolling Stone magazine:
9. Hillary Clinton was feeling springtime and posted this photo of herself from 1995:
10. Chris Pratt (who is on the bottom right) celebrated #NationalSiblingsDay by sharing this photo of himself alongside his siblings and cousin in 1983:
11. Michelle Obama celebrated #NationalSiblingsDay by posting this photo of herself and her older brother, Craig Robinson, in the late '60s:
12. Jake Gyllenhaal also celebrated #NationalSiblingsDay and shared this photo of himself and his older sister, Maggie Gyllenhaal, in the early '80s:
13. In honor of Bette Davis's birthday, celebrity photographer Terry O’Neill posted this photo of the late iconic actress, taken in 1986:
14. Drew Barrymore celebrated the 20th anniversary of her classic movie Never Been Kissed by sharing this collage of scenes from the movie:
15. Amy Sedaris celebrated the 20th anniversary of her cult classic TV series Strangers with Candy by sharing some photos from the series:
16. Mandy Moore posted this photo of herself rocking some serious early '00s fashion:
17. Reese Witherspoon shared this photo of herself from the '00s:
18. Mariah Carey celebrated the 10th anniversary of her No. 1 single "Touch My Body" by posting the cover art for it:
19. Iman shared the different covers taken for Vanity Fair's special 2007 Africa Issue:
20. Amanda Seyfried remembered when she did a campaign for Givenchy in 2013:
21. Ariana Grande shared this amazing clip of herself singing along to NSYNC's "I Drive Myself Crazy," taken during their 1999 Pay-Per-View special, 'N Sync 'N Concert:
22. And finally, Miley Cyrus celebrated the 10th anniversary of her iconic film Hannah Montana: The Movie by sharing this promotional photo from it:
Happy Anniversary to this queen #HMTHEMOVIE