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    Re: Timesight at sunset?
    From: Doug MacPherson
    Date: 2013 Jan 22, 14:57 -0800
    All:

    I just returned to my home in California and was able to work out the sunset solution for myself using Nories and the hav(t)=sec(L)cosec(p)cos(s)sin(s-h) formula found in my 1938 rendition of Bowditch. (see attached).

    The actual Latitude and Longitude of my position were:

    Lat: 20-1.4 N
    Long: 155-49.3 W

    My solution was off by 4.3 nm (need to work on my eyesight correction factor:) )

    Thanks to everyone that provided help!  Especially Robert Bernecky, who provided the elegant solution using Martelli's Tables.  I just got my copy of Martelli's in the mail (printed in India!).

    Doug

    On Wed, Jan 9, 2013 at 11:11 PM, Dwmacpherson2000 <dwmacpherson2000---.com> wrote:
    All:

    Sitting on a beach on the west side of the big Island of Hawaii, sans sextant, what is a frustrated navigator to do?

    With a perfect sunset every night, can it  be exploited for an accurate longitude with a time sight?

    Alas, Equipped only with my iPhone, and my eyesight, I think I will need some help if any are willing. I don't have my copy of Norries or an almanac. 

    On January 9, 2013 the upper limb of the sun dropped below the horizon at 18:00:35 Honolulu time (on my i-phone) with a noticeable green flash :)) I was standing on the beach at the water's edge. I am 6 feet tall. My latitude is 20.023 degrees north. I cannot determine index correction, my eye doctor is back in California :)

    78 degrees Farenheight. 29.89 inches of mercury. 

    Can anyone help me with determining what my longitude is?  The sun's azimuth at that time?

    Also were sunsets and sunrises ever used for practical purposes for navigation besides determining azimuth for compass error?

    Doug 

    Sent from my iPhone

    On Dec 14, 2012, at 14:39, Dwmacpherson2000 <dwmacpherson2000---.com> wrote:

    Thanks!

    Sent from my iPhone

    On Dec 14, 2012, at 4:23 PM, "Greg Rudzinski" <gregrudzinski---.com> wrote:

    Doug,

    The time sight method sight reduction formula looks to have a user friendly format for calculator crunching. The trig calculator doesn't meet your non electronic requirement but perhaps should be reconsidered if equipped with solar power. The best non electronic time sight reduction as for speed of solution is the slide rule if a small amount of calculation error is acceptable. I did a full trig table solution and found it difficult and error prone. If you are good with trig tables then this may be an option. The Weem's secant time sight table remains to be evaluated. See attached reductions for trig table, slide rule, and calculater compared.

    Greg Rudzinski

    [NavList] Re: Longitude by Time Sight...good enough at sea?
    From: Doug MacPherson
    Date: 13 Dec 2012 20:16
    Wow, Great discussion. Really appreciate Frank's insight on the Sumner Line and the time sight, also the other great stuff sent my way.

    For me, the choice of the time sight and ex-meridian etc. comes down to my parameters for what I want from my navigation "solution".

    There are many solutions out there. From the gyro/satellite (electronic) solution I was using as a bridge officer in the USN in the 80's, to the Polynesians navigation system (relying on the sun and stars, winds and clouds, seas and swells, and birds and fish) and everything in between. Choose your parameters and then the solution will follow, i.e. electronic/non electronic, tables/non tables etc.

    My current parameters include:

    1. Non electronic and based on accurate sextant measurements and an accurate chronometer.
    2. As little plotting as possible.
    3. As little tedious mathematics (prone to mistakes) as possible.
    4. As few books as possible: Norie, Bowditch, Hansen are OK. One book vs. volumes.
    5. The best accuracy possible given 1 through 4.

    Given all your helpful feedback, my solution would appear to include: Latitude by Polaris, Latitude by Ex-Meridian, Latitude at noon and Longitude by time sight. Books to include, a up to date nautical almanac, Norie's (or Bowditch), Hansen's, and some tables for time sight (Martelli?), (although I am happy with Norie's and the haversine formula's for the time sight). These would appear to be enough.

    Certainly, if safety required, the LOP would be utilized (modern methods) .....as well as the handheld GPS :)

    Thoughts?

    Thanks,

    Doug

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