Hi Richard,

I cannibalized a private e-mail I sent about three years ago on the
subject of projections for star charts, added some comments about
lunar cartography, "sort of" HTML-ized it, and posted it at

http://www.projectpluto.com/project.htm

The "Yarkovsky effect" is one in which an asteroid heats up in
sunlight, rotates a bit, and emits thermal radiation preferentially
in that direction (by the time it rotates around a bit further, it's
cooled somewhat and radiates less). The result can speed it
up or slow it down enough, over millions of years, to do things
such as bring main belt objects into the inner solar system. An
absurdly small effect, but over enough time, it accumulates and
you have to take it into account. (It matters most for smaller objects,
which is a Good Thing; there is no risk that this will cause the
major planets to fall into the sun, or spiral outward toward
interstellar space.)

-- Bill