The above YouTube rendering is attributed to "Rick Lee · Lorraine Lee Hammond", so I guess the latter is the singer and the songwriter's spouse (widow).

The lyrics say "... who did surely prove ...", which I got confused for lack of proofreading. On the tombstone, it says "... discovered ...", quite a claim as well.

The words "the old astronomer" are indeed found on the stone, perhaps already meant as an ironic reference to the Sarah Williams poem? (The adjective is inadequate, since the dead are neither old nor young.) Thus, the title is somewhat misleading, but by no means to be criticized.

A fine song, as I said; what a pity that the writer is deceased, too.