> Clearly the rise/set of the upper limb more closely resembles the
> visual impression of an observed rise/set: we think the "sunrise"
> occurs when we see the first part of the solar disk, not when we see
> precisely half the solar disk. However, when we use the upper limb
> of the Moon to compute lunar rise/set times, we encouter a problem:
> the upper limb of the Moon is fairly often dark! The "proper" way to
> deal with that is somewhat complex though: one could compute the
> rise/set time of the uppermost part of the ILLUMINATED portion of the
> lunar disk. I've never seen any program or heard about anyone
> actually doing this though.

I don't think there would be any practical benefit in attempting to do this.
Rise and set times can only realistically be calculated to an accuracy of
the nearest minute or so anyway, due to the uncertainties of refraction in
the "real world" which can vary significantly over a very short timescale.
This would be an exercise of purely academic interest, IMHO!

Regards,

Chris
---------------------------------------------------------------
Chris Marriott, SkyMap Software, UK
e-mail: chris@... Web site: http://www.skymap.com
Astronomy software written by astronomers, for astronomers

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