The Equation of Time, old time navigation know-how in the modern world

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now excited to have Ben Stein as very able publisher, webmaster, and editing colleague. Panbo is going to the next level in 2019 and beyond.

15 Responses

  1. DougP says:

    Thanks Ben!!!
    This brings back some wonderful memories!!
    Makes me want to haul out my Tamaya Spica and take a round of sights!! 😉

    • Thank you, DougP. You inspired me to pull out and lubricate the Heath Hezzanith I bought almost new on a St. Thomas dock in 1971. It could use new mirrors but I think it could still work. I also have a Walker Excelsior IV Taffrail Log that I recall as old school even in the 70’s. It too got oiled and seems fully functional (if I found the right line to replace the one some garage critter destroyed).

      You might also enjoy this old entry about celestial mechanics and why observed sun altitude at LAN subracted from 90° plus or minus Sun Declination equals your Latitude (which is also visible in the NOAA Solar Calculator results):

      https://www.panbo.com/the-equinox-celestial-mechanics-pesky-true-wind/

      And/or Charlie Doane’s “Celestial Reasoning…”

      http://www.wavetrain.net/techniques-a-tactics/101-celestial-reasoning-quick-a-dirty-noon-sights

      • DougP says:

        A Taffrail log??? Now that IS seriously Cool! AND Seriously old school!!!
        Like me!
        I kept the Spica onboard for years long after putting a Decca 801 (?) Satnav (TRANSIT) on the Luna 50 I bought in France to bring her back to SoFL in ’85, but I still took a noon site, just to keep my hand in. The Transit systems were pretty cool, often giving you a 1/2 mile fix every fifteen minutes to a few hours! 😉
        When we flew to France to pick up the boat, I also took my old TI Loran with me.
        Loran C AND SATNAV on a 50 foot sailboat, with a Vetus jet bowthruster!! Were we hot stuff or what???

        • You can sort of see the Walker at work in this 1978 offshore photo…

          https://cdnkey-bb0b.kxcdn.com/assets_c/2012/12/Alice_1978_w_Dixie_at_helm_cPanbo-6666.html

          …but I will honor it more in a future EdBlog. It certainly improved our DR work.

          I also still have that DIY plywood fishing reel, and sometimes we dared trail both at once. The SOP was no sharp turns and haul in the log before the fish, but we still endured some terrible tangles.

          • DougP says:

            GREAT PIC! truly old school! What vane was that? Looks like it far predates the old Sailomat which as the only vane I have any experience with.

          • I can’t remember the brand name, Doug, but think it started with an R. Nicely self-contained, simple vertical vane to trim tab, but aluminum parts caused some trouble I recall. This was the last offshore trip on Alice (daughter on her way) and I’d just installed the vane a few months before, so I didn’t get to use it very much.

  2. An interesting tidbit from the stellar Wikipedia Equation of Time entry:

    “The right time was originally considered to be that which was shown by a sundial. When good mechanical clocks were introduced, they agreed with sundials only near four dates each year, so the equation of time was used to ‘correct’ their readings to obtain sundial time. Some clocks, called equation clocks, included an internal mechanism to perform this ‘correction’.”

    https://en.wikipedia.org/wiki/Equation_of_time#History

    It must have been hell on airline schedules.

  3. Larry Hall says:

    Thanks for the article, Ben, and Happy Holidays! Old enough to have used HO 214, 229, and 249 for sight reduction I now revel in the use of a $15 app for my iPhone called ‘Celestial’ by Navimatics. Check it out!

    • DougP says:

      Hi Larry,
      The reduction apps are amazing.
      Do you remember the small, 1980s, sight reduction calculator that came in a small wood box to match our sextants? I can’t remember the brand, but I thought I’d died and gone to heaven when I got that! 😉

      • “Tamaya” maybe? I never owned one but spent time offshore jealous of those who did. The StarPilot looks like the ticket now:

        https://www.celestaire.com/product-category/computersoftware/

        • DouP says:

          Tamaya might have sold them but didn’t make them.
          But I just found it on Google:
          Celesticomp complete with the mahogany box!
          I was truly kickass with that! 😉
          That Starpilot is very nice with the graphing capability! Would be wonderful for sites in rough conditions!

          • Andrew Howe says:

            Unfortunately, the Celesticomp is no longer made or serviced/updated….I found this out when mine died in the middle of the 2015 Marion Bermuda Race. Luckily a crew member had brought a spare so I was spared the drudgery of the tables (which were on board as well). For the 2017 race I downloaded the “Celestial” iPhone app from Navimatics, which works great! For quick practical work the app can’t be beat, but it is still fun (and smart) to recall and explore the mechanics behind celestial navigation. Sort of like keeping paper charts at hand, and actually putting a pencil mark on a chart once in awhile!

  4. JB says:

    Perihelion — Earth’s closest approach to the Sun — is in very early January. So, during northern hemisphere winter, the Earth is moving around its orbit faster than it is in summer (Kepler’s second law “equal areas in equal times”), which means that the angular position of the Sun relative to the stars changes more quickly in winter, hence the area of that portion of the figure 8 analemma is larger.

    13000 years from now the situation will be reversed owing to precession of the equinoxes.

  5. Wil Bailey says:

    It turns out I now have two ‘sunguns’ – one given, one inherited, neither actually been used yet. There’s an Astra IIIB ( presented to me by HRH ) and a Zeiss Trommel ( bought by boatbuilder F-in-L before his last illness ). Which one to keep?
    I also had 3 trailing or taffrail logs. I gave one to a would-be GGR competitor, who didn’t go further than Spain. Maybe I’ll do better….

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