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John

I think you do see time diagrams in post WW2 textbooks e.g. ‘Celestial Navigation for Yachtsmen’ Mary Blewitt, and ‘Celestial Navigation’ Tom Cunliffe.  It’s just the diagrams aren’t so all-encompassing and pedantic as in 1930s textbooks.  Modern authors probably don’t even call them ‘time diagrams’.  I had to look the name up even though I’ve always used my own baby versions.  The reason might be that around the 1930s celestial was in a period of transition moving from right ascension to hour angles.  Nowadays, you rarely hear right ascension used by practical navigators, so for all practical purposes the diagrams can be much simpler.

All the author wants you to remember is LHA Body= GHA Body + longitude of the observer E, or – longitude W, but if they just said that, the beginner wouldn’t have a clue what the author was talking about.  Therefore, they use time diagrams to make it easier for the beginner to understand.  If you’re doing celestial pre-computing every day, or if you have it all written into a prompting form, you don’t need a time diagram.  If, on the other hand, you have a C-minus memory like me, and are saving your last pre-comp sheet for posterity, except you can't remember where you hid it, a simplified time diagram can help.  Mine is just a dot for the pole (north in my case), and three spokes: Greenwich, the observer, and the body.  Greenwich goes straight down, and westwards is clockwise.  Why do I do it that way and not the way the magnificent examples appearing on You-Tube use?  Well, that’s the way Flt Lt Watkins taught us to do it on No2 ANS in 1967.  DaveP