NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How often can you see the sunrise/sunset - PLEASE HELP?
From: Mike L
Date: 2007 Dec 6, 06:15 -0800
From: Mike L
Date: 2007 Dec 6, 06:15 -0800
Marcel, yes, I think you are right! If I could relate sun angle to the probability of seeing the sun through a "cloudy", "clear sky", etc, then if I could assume that everywhere had similar clouds (I'm laughiing!) then I could work out the probability of seeing the sunrise/set! I tried to find out the height of typical clouds and failed! However, midlevel clouds are between 2000-5000m high. So, if the cloud is 2-5km high, for there to be a view through the clouds there must be a hole such that the top of the clouds at 5km high are some 250km away and the bottom of the cloud is some 160km away. To see a complete view of the sun, the hole in the clouds must be such that every observer along a 32'= 32nautical miles path away from the sunset is able to see the sun through this hole, so the nearest cloud base must be 160km-32*1.852 (= 100km) must be able to see. So, assuming the clouds are from 2-5km then the hole in the clouds must be some 250-100 = 150km long by 60km wide whilst a similar cloud at midday need be only 17m wide! CALCULATIONS! Earth's radius R = 6370km Angle of arc around earth to base of cloud = cos-1(R/R+2) = 1.4degree Angle of arc around earth to Top of cloud = cos-1(R/R+5) = 2.3degree Distance = R*tan(angle) Or using Pythagooras: R=earth's radius H=Cloud height Distance = ((R+H)^2 - R^2)^.5 = (H^2 + 2*H*R)^.5 which is approx 112*square root of cloud height in km On Dec 6, 1:07 pm, "Marcel Tschudin"wrote: > Mike, > > On Dec 6, 2007 2:33 PM, Isonomia wrote: > > > ... > > 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. > > You could e.g. put the daily data of the Wunderground Web-page (where > you likely may have hourly information on cloud coverage) in relation > to the sun's position above the horizon. This may allow you to gain > eventually an idea on which of all the different meteorological > parameters are important for your problem. However, I don't think that > statistical analyses will be able to tell you more than very rough > tendencies, this as a result of the large (temporal) variations in > cloud coverage and thus also of the hole sizes. > > Marcel --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---