An essential component in Astro was AP 1629 (IIRC) the Air Almanac. It was issued every 6 months (or maybe 4) and tabulated the sunrise/sunset, SHA for Aries, the Sun, Moon, and planets. Some years ago they Almanac tables were reduced to sunrise/sunset only making it impossible to even take heading checks unless one used ephemris or a casio mini-computer that would enable you to work out accurate alt/az for any navigational body.
The E3 crews used these to enable them to conduct heading checks on the kollsman sextant. However an E3 surveillance orbit was not suitable for taking heading checks.
On the Vulcan, in the 1970s, a technique called fix-monitored azimuth (FMA) was used to correct the heading reference gyros (HRS). Basically any azimuth error could be corrected from an accurate fix. FMA could be used to justify not doing an astro heading check which of course was difficult at low-levels, below cloud, in a Nimrod.
Astro was taught at Nav School in the late 80s but probably dropped soon after.