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    Re: How often can you see the sunrise/sunset - PLEASE HELP?
    From: Mike L
    Date: 2007 Dec 5, 12:00 -0800

    Marcel,
    
    that's very interesting because we (in the UK) get presented with the
    weather forecast as if the weather is independant of the time of day.
    But thinking about it, the clouds do bubble up on a hot day so it must
    get cloudier on average toward the end of the day.
    
    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?
    
    Another question I have is how big would a hole in the clouds have to
    be to see the whole sun at sunrise/set and how far away would it be?
    My initial thought was that being on the horizon, the light would
    virtually be passing horizontal through the clouds, which would mean
    the hole would have to be absolutely massive, but then I realised the
    clouds would be at quite a hieght and so .... at which point my mind
    goes numb!
    
    
    On Dec 5, 5:34 pm, "Marcel Tschudin" 
    wrote:
    > As a mostly silent member of this list, I may eventualy add something
    > to this subject.
    >
    > I'm interested in refraction near the horizon. For this I regularly
    > observe sunset events.
    >
    > The amount of cloud cover depends to a large extend on the temperature
    > (and of course also on the atmospheric pressure). As higher the
    > temperature as more the air can absorb humidity and thus reduce the
    > number of clouds.
    >
    > At my present location at about 40N the clouds mostly disappear during
    > summer days due to the high temperatures of around 30C. During this
    > time a lot of observations are therefore possible. This changes
    > drastically during the colder seasons where the number of days with
    > unobstructed sunsets become rare. This seasonal dependency is trivial,
    > we all know it from our own experience.
    >
    > However, in addition to this seasonal cycle exists also the daily one,
    > i.e. the temperature has also a more or less pronounced diurnal cycle.
    > The highest temperature within a day occurs generally about 2 to 3
    > hours after the sun's transit. In the case of a circumpolar sun it's
    > about 1 hour. The lowest temperature within the diurnal cycle occurs
    > between about 0 to 1 hour before sunrise and about 1 hour after the
    > lower transit in case of the circumpolar sun.
    >
    > The behaviour of the diurnal temperature cycle suggests that the
    > chances for finding a hole in a totally covered sky are probably best
    > in the afternoon.
    >
    > Marcel
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