"Stuart Levy" writes:

I browsed a bit but couldn't find any on-line references suggesting
specific values for rates of node advance for Mercury or Venus.

From the 1992 edition of the Explanatory Supplement to the
Astronomical Ephemeris, p. 316, we find for J2000 for mean equinox and
ecliptic of that date:
Mercury's node = 48.33° - 4.4630"/year
Venus's node = 76.68° - 9.9689"/year

However, the inclinations are not constant, so these are not
representative of the long-term behavior. For a double transit, you
would want to search for times when the inclination between the orbital
planes of Venus and Earth was a minimum. Then Venus transits would be
frequent enough that nodal alignments would be long-lasting, opening up
many opportunities for double transits.

Incidentally, I've added an appendix about transits seen from other
solar system planets to my paper on the black drop effect at
http://metaresearch.org/home/viewpoint/blackdrop.asp. -|Tom|-


Tom Van Flandern - Washington, DC - see our web site on replacement
astronomy research at http://metaresearch.org