Greatest hits collections are notoriously bad places to start learning about an artist’s history, but In the Orbit of Ra, an anthology of the late outsider jazz legend Sun Ra overseen by his longtime saxophonist Marshall Allen, is an exception. In a career spanning over five decades, the pianist, space gongist and bandleader, born Herman Poole Blount in 1922, released literally hundreds of LPs— many via his own Saturn Records. In the Orbit of Ra pulls in swinging big-band exotica (“The Lady with the Golden Stockings,” “Plutonian Nights”), deft pop charts with dense vocal harmonies and strange strings (“Interplanetary Music”), ineffable singing by June Tyson (“Somebody Else’s World”), haunting cosmic dust-ups (1972’s “Astro Black”), righteous avant-drum machine experiments (1978’s “Dance of the Cosmo Aliens”), and solid takes of stone underground classics (1960’s “Rocket Number Nine” and the immortal refrain of “We Travel the Spaceways”). If one has been putting off learning about the cosmic wonder that is Sun Ra, then In the Orbit of Sun Ra is a generous rocket ready to take off for the planet Venus.