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    Re: Cugle - longitude at sunrise and sunset
    From: Gary LaPook
    Date: 2013 May 2, 01:27 -0700
    Here is a simple way to see  why Noonan would never have planned to use a sunrise observation. I think we have all been on a beach watching the sun go down. Think back to your own observations. Were you able to actually see the upper limb of the sun disappear behind the sea horizon? Hmmm?  Probably not unless you have looked for it many times. The vast majority of the time there are clouds between you and the horizon and even more clouds beyond the horizon and the sun sinks behind the clouds, not behind the sea horizon. The clouds prevent you from accurately determining the time the sun is actually aligned with the true horizon and every four seconds of error in this timing causes a one nautical mile error in the derived position line. It is an even bigger problem if trying to do this in flight because the horizon is much farther away so providing a much greater opportunity for clouds to block the view. Also in flight the horizon is so far away that the air over the ocean is rarely clear enough to see all the way to the horizon. For example, from 10,000 feet the horizon is 130 NM away, how often do you have 130 NM visibility? (Over the desert, where the air is very dry, you might get this kind of visibility but not over the ocean where the air in moist.)

    In 2009 I sailed across the Atlantic on the Royal Clipper and posted about it before, see

    http://www.fer3.com/arc/m2.aspx?i=110827&y=200911

    We were 10 days at sea from Tenerife to Barbados so there were ten sunrises and ten sunsets and I was up every morning before sunrise to shoot the stars and everybody was on deck to catch the sunsets. So, how many sunsets and sunrises was I able to see clearly and record the time so that I could work out a line of position as recommended by van Asten as the sun set or rose from the sea horizon? Just three times out of a possible 20! Clouds blocked the observations 17 out of 20 times. And that was from sea level, on a ship where the horizon was only 5 NM away, not in an airplane. You want to bet your life on these odds?

    gl

    --- On Tue, 4/30/13, Gary LaPook <garylapook@pacbell.net> wrote:

    From: Gary LaPook <garylapook@pacbell.net>
    Subject: [NavList] Re: Cugle - longitude at sunrise and sunset
    To: garylapook@pacbell.net
    Date: Tuesday, April 30, 2013, 1:46 PM


    Thanks.

    Hm-mm, "Not to be entirely relied upon....a fairly good idea of his longitude" when taken from a ship at sea level. I notice that the computation requires the use of haversines, Noonan only had HO 208.

    Are you going to bet your life on this procedure, looking for a small island from a plane without knowledge of the proper dip and negative altitude refraction corrections from altitude? Another thing that people forget, procedures that might be useful on a ship, with virtually unlimited endurance, are not very useful in a plane with only a couple of hours of fuel. If the shipboard navigator can't get an accurate fix when approaching a landfall he can heave to or stand off and on until he gets one. A flight navigator doesn't have this luxury.

    gl

    --- On Tue, 4/30/13, Dave Walden <waldendand---com> wrote:

    From: Dave Walden <waldendand---com>
    Subject: [NavList] Cugle - longitude at sunrise and sunset
    To: garylapook---net
    Date: Tuesday, April 30, 2013, 12:56 PM


    from my 1938 cugle
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