It is one of rock’s least-likely masterworks. Van Morrison had made a name for himself as the lead singer of the Belfast bar band Them, which achieved immortality with the garage anthem “Gloria.” He then signed a solo deal in the US, skimming the Top Ten with the irresistible singalong “Brown-Eyed Girl,” but he dismissed the album that came from those sessions. Signing with Warner Bros. Records, Morrison then assembled a bunch of jazz-based players, took them into a New York studio, and emerged two days later with Astral Weeks, a languid, impressionistic, utterly gorgeous song cycle that sounded like nothing he had done previously — and really, nothing anyone had done previously. Morrison sings of lost love, death, and nostalgia for childhood in the Celtic soul that would become his signature. Astral Weeks didn’t reach the charts, but its mystic poetry, spacious grooves, and romantic incantations still resonate in ways no other music can.