Lunar occultations/retraction
Bill J Gray Mar 27, 2002
Hi Paul,
In such a case, Guide will sit and spin until you hit the Escape
key to stop it.
I should be able to fix this (at least in most cases) by including
some code that says, "if a star is more than about 7 degrees
from the ecliptic, it absolutely cannot be occulted by the moon."
The strict limit is 6.6 degrees, as discussed by Jean Meeus in
_Astronomical Algorithms_. He also discusses the case of Pollux,
which is currently unoccultable, but which was occulted as recently
as 30 September -116; and of Delta Sagittarii, currently occulted
from time, but which will be occulted for a final time on 1 October
2359. In both cases, proper motion will draw each star outside
the 6.6-degree band.
I suppose I could weasel out by saying that at some point, even
Polaris is going (or would be) occulted. But there is no chance of
Guide computing such distant (millions of years) occultations with
even a shred of accuracy.
Incidentally, Jari, I retract my earlier statement. It's true
that Guide will sometimes change times because you select an
occultation, and it had to do some searching before it finds an
eclipse. In this case, though, there _was_ an occultation of
Saturn on that date.
-- Bill