Yes, I’m well aware that no sound can be heard in the vacuum of space. Still, I am rather taken by the theory of Pythagoras known as the Harmony of the Spheres, in which he postulated that the sun, moon, and planets all emit their own unique hum based on their orbital revolution. If I could indeed hear the music of those spheres as they move through the heavens, for me it would be the celestial hum at the end of the first section of the Bachianas Brasileiras No. 5 by Heitor Villa-Lobos (1887-1959), Brazil’s preeminent composer of the 20th century. Although the Moon is the major actor at the heart of the Portuguese lyrics, it’s the hum at the end that transports me.
Performed by an ensemble of eight cellos and soprano, there are many interesting recordings to explore, starting with the first: recorded in 1945 (first section only), shortly after that section was written, with the composer as conductor accompanying Bidu Sayão. I’m partial to versions sung by, seemingly surprisingly (but perhaps not), Joan Baez (conducted by Maurice Abravanel) and Marni Nixon (conducted by Felix Slatkin). But the first version I heard many years ago remains the one I hear when I gaze heavenward: also with Villa-Lobos conducting, it features the radiant voice of Victoria de los Angeles. Critics may quibble about the conducting, but all agree that her singing is sublime. This recording, found below, includes both sections:  Ária (Cantilena) and  Dança (Martelo).
As for that heavenly hum, listen for it starting at about 4:55, continuing through 6:11. Pay special attention (and perhaps boost your volume just a tad) as it floats even higher into the heavens at 6:03.