Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: How often can you see the sunrise/sunset - PLEASE HELP?
    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
    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!
    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" 
    > 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 unsubscribe, send email to NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site