Transits in Guide

Bill J Gray Jun 25, 2003

Hi Lawrence,

In theory, one can compute accurate transit data for asteroids
with Guide. In practice, you'll find that in most cases, the
orbits are based on short arcs, so the accuracy won't be
everything we might want.

A while back, I did something along the lines of what Bob
Elliott suggested, using the method for filtering asteroids
described at

http://www.projectpluto.com/update7.htm#asteroid_filtering

I set the filter to be

ASTFILTER=q<1.03 & d<1.03

...that is, considering only asteroids whose perihelion would be
inside that of the earth's orbit, and that were less than 1.03
AU from the earth (so that objects on the far side of the sun
were discounted). I right-clicked on the sun, then did some
animating in 'moving target' mode. As I recall, I did see one
"transit", but of an object with an uncertainty so large that
the "prediction" was meaningless. (It also fell short for
the reason described by Arild in an earlier post: its
apparent diameter was a few milliarcseconds, not something
apt to be observable. I'd expect that to be the rule rather
than the exception.)

Artificial satellites are another matter. Several people have
computed transits of satellites across the sun and moon
using Guide, with success.

-- Bill