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Frank:

On Tue, 2 Nov 2004, Frank Reed wrote:

> Maybe we should experiment. How many occultations
> can you observe during the
> next couple of months?

I will experiment, of course. The main obstacle is the bad weather:-(
I suppose there are many occultations, if you take
more stars into account. (Unfortunately the nautical almanac
has too few stars:-(

My main question was how precisely you can time a sunrise/set
and what is the role of the refraction here.
Unfortunately, I cannot experiment in this area
for the simple reason that I have no horizon:-(

> the way, if you're excluding sextants, should you
> also exclude binoculars, or do we permit them?

I'd try both variants. Though I do not expect much improvement.
Maybe it will help with Moon/stars.
But what sort of filters can be used to look
at the Sun through binocilar, so that the horizon remains visible?

> with using the period when the Moon is moving with dark edge
> trailing, too. An
> attentive observer can time emmersions almost as well as immersions.

This should be harder. But I have not experimented yet.

> How much error are you guessing based on variable refraction?

I have no idea. Chauvenet wrote somewhere, citing Bessel,
that "No reliable refraction tables can be made for altitudes
less than 5 degrees". I think, only an experiment can help
to decide.

I invite everyone to participate in this simple experiment:
next time you enjoy a sunset in sea, look at your watch
and record the time when the Sun touches the water:-)

Alex.

   

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