Space, specifically, the International Space Station.
Coleman, an amateur flutist, and Anderson played a portion of the song "Bourree," an arrangement of which Anderson and Jethro Tull performed during their 1969 U.S. tour as Neil Armstrong and Buzz Aldrin stepped on the moon. Coleman played her part from 220 miles above Earth late last week. Anderson played his part while on tour in Perm, Russia, during the weekend. The two parts were then joined.
Ed's blog post about the collaboration