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computer rant
It's amazing and appalling just how many questions for "how to get <computable almanac data> in bash" wind up being "just use curl on <website> and parse that data" answers.
Just-use-curl folks, I know it's shocking, but...
I have a computer.
It's pretty good at computing.
I don't want to depend on someone else's computer, that might get turned off at any time, and that's only reachable by an often crappy 'Net connection.
computer rant
It took literal days of searching, poring over hundreds, maybe thousands, of results, but I did finally manage to find what I was looking for: Programs that compute sun and moon data (one in Perl, another in Ruby), then print them in a form shellscripts love.