First recorded by The Off-Broadway Cast of Hair (1967).
Hit version by The 5th Dimension (US #1/R&B #6/CAN #1/UK #11/AUS #3 1969).
https://youtu.be/x5kNrTtRqI4
From the wiki: “‘Aquarius/Let the Sunshine In’ is a medley of two songs written for the 1967 musical Hair by James Rado & Gerome Ragni (lyrics), and Galt MacDermot (music). Originally recorded as separate performances by the cast of Hair, the medley recorded by The 5th Dimension became one of the most popular songs of 1969 worldwide. ‘Aquarius’ was ranked #33 on the 2004 American Film Institute’s 100 Years … 100 Songs listing (in the motion-picture adaptation of Hair, produced in 1979).
“The lyrics of this song were based on the astrological belief that the world would soon be entering the ‘Age of Aquarius’, an age of love, light, and humanity, unlike the then-current ‘Age of Pisces’. The exact circumstances for the change are ‘When the moon is in the seventh house, and Jupiter aligns with Mars.’ This change was presumed to occur at the end of the 20th century; however, major astrologers differ extremely widely as to exactly when: Their proposed dates range from 2062 to 2680. ”
The Broadway Cast of Hair, “Let the Sunshine In” TV performance (1968):
The 5th Dimension, “Aquarius/Let the Sunshine In” (1969):