Us and Them began as Rick Wright's piano piece The Violent Sequence, written for Michelangelo Antonioni's Zabriskie Point and turned down in Rome in 1969.
Interstellar Overdrive, the long instrumental on The Piper at the Gates of Dawn, started when Peter Jenner hummed Love's My Little Red Book to Syd Barrett out of tune.
Astronomy Domine opens The Piper at the Gates of Dawn, recorded at Abbey Road on 11 April 1967 with Syd Barrett on the low vocal and Rick Wright on the high one.