# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Will the sun shine?
From: Mike L
Date: 2007 Nov 29, 15:27 -0800

```How can the sun be more visible at sunrise and sunset?

Surely the lower down in the sky, the more obtuse the angle through
the clouds and therefore the larger the hole in the clouds needs to be
before the whole disc can be seen. As a first approximation I would
imagine the probability is something like:

p(observing sun) = P(observing at noon) * Sin(sun altitude)

Clearly this can't be quite correct as it implies the sunrise/sunset
is never completely visible. Perhaps this is because the cloud base is
above the observer and therefore the angle of sunlight through the
clouds is alway significantly greater than 0.

Thinking about it, at great distance the main part of the clouds
observable is the side of the clouds, so the height of the clouds must
come into the equation in some increasing effect such as cos (SunAlt)
- but just now I can't think of the maths behind it.

Mike

On Nov 29, 6:24 pm, Fred Hebard  wrote:
> I'm not sure what you mean.  The sun often pokes through the clouds
> at noon.  I suppose this occurs because it's the time of maximum
> incidence of the rays.
>
> On Nov 27, 2007, at 8:16 PM, Peter Fogg wrote:
>
>
>
> > Fred Hebard wrote:
>
> > The sun is often visible at solar noon, even on heavily overcast
> > days.  Not as often, it is frequently more visible at sunrise and
> > sunset than other periods of daylight, with the exception, mentioned
> > above, of noon.
>
> > How so, Fred?
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