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

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Re: How often can you see the sunrise/sunset - PLEASE HELP?
From: Mike L
Date: 2007 Dec 6, 04:33 -0800

```Marcel,

the problem with figures on average cloud cover is that they tell me
how often the sky above the observer can be seen, but not how often
the sky at the horizon can be seen. E.g. if the holes in the clouds
were 1km across and even a few hundred meters high, by the time they
were "on the horizon", they would have completely disappeared.

Obviously its a lot more complex, because it all depends of the
variation in "hole" size and whether this hole size when viewed from a
very obtuse angle will be large enough to view the sun.

So, whilst cloud cover should give a very good indication of the
probability of seeing the midday sun (when the sun is itself high due
to latitude and season), I can't see how to relate it to the
probability of seeing a sunset/rise.

but thanks again for your input, I'm beginning to think the only way
of getting data is to buld a sun detector (another post I think!)

Mike

On Dec 5, 11:29 pm, "Marcel Tschudin"
wrote:
> Mike,
>
> On Dec 5, 2007 10:00 PM, Isonomia  wrote:
>
> > ...
> > But I'm still stuck on even very basic information link e.g. would the
> > probability of seeing the sun and sunrise/set be the same in winter
> > and summer?
>
> The answer to this you find in my previous reply. Isn't it also in the
> UK in summer generally hotter than in winter? If so, then the chances
> are that there is generally a greater cloud cover in winter than in
> summer.
>
> If you would like to find out more on this I invite you to do some
> statistical analysis yourself. The data are readily available through
> the Internet. Have a look here:http://www.wunderground.com/cgi-bin/findweather/getForecast?query=uni...
> After selecting a place you like to investigate you come to the
> Web-page with the current conditions.
> Look on this page for "History & Almanac" and select a previous day
> and press "GO".
> You receive now all the measurements of the station at this day, which
> - depending on the station - may be up to about half-hourly intervals.
> In the last column you find the cloud cover. The terms like "Scattered
> clouds" or "Overcast" etc. refer to approx. percent values of cloud
> coverage. (Since I don't know this relationships, you have to find out
> on this yourself.) From this page you can retrieve the "Daily" data.
> For doing statistical analysis you may want to have the information in
> form of a data file. For this you go down at the bottom of this page
> and select "Comma Delimited File" and transfer the data by copy/paste.
>
> For a statistical analysis you probably may want to have data of a
> complete month, a year or even several years. For this you go to the
> top of this Daily Summary page and select the the "Weekly", "Monthly"
> or "Custom" data. The Comma Delimited Files of those data have the
> amount of cloud cover as a number; I'm not sure but I think the value
> refers to multiples of 1/8th.
>
> The comma delimited files have the advantage to be red into a
> spreadsheet program like Excel where you can perform your analysis
> work.
>
> I think that's all what I can help you on this subject. I wish you
> good luck. Don't forget to inform those who might be interested in the
> results (like me) on your results.
>
> Marcel
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