I plucked some bits and pieces out of the Stellarium source code and built myself a planetary conjunction finder, looking for times when planet A is at inferior conjunction as seen from planet B. Specifically, I was looking for transits. Sure enough, I found what is apparently the rarest transit of all: a transit of Uranus as seen from Neptune.

It's a picture-perfect transit. The center of Uranus passes a bit more than 2" from the center of the Sun; it looks like a little black bulls-eye at the mid point. With 43 hours between first and fourth contact, Neptune makes almost three rotations during the transit.

And maybe at 6 August 46,915 23:14 UTC we'll have an outpost or two on the moons of Neptune that can actually image this transit.

Since I don't expect to live quite that long, I'd like to know how accurate the VSOP87 model is over such a vast expanse of time. How confidently can I say that Uranus will actually transit the Sun, as seen from Neptune, at that time?