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Passing Under the Sun

October 6, 2011

Day 8

Local Noon Position–
By GPS: 02.55.04S by 147.20.66W
By Sextant: 02.58S (Dead Reckoning, explained below) by 147.20S

Course: 25 degrees true
Speed: 4.8 knots
Wind: 7-10 ESE
Sea: 2 – 4 E
Sky: 20% occluded. Unsubstantial cumulus scattered throughout sky. Bar: 1012. It seems not to move at all.
Temp: 78 degrees

MILES
Since last noon: 123
Total for passage: 854
Daily Average: 122

Mileage Note: We’re still losing a knot or better to current (or something). Murre averaged 6 knots and much better yesterday afternoon and into the night. In the early morning the wind began to decrease, so we packed on more sail (took the reef out of the mizzen) and are now averaging 5.0 to 5.5 through the water, none of which is, sadly, reflected in speed over ground.

Passing Under the Sun

Today was a milestone from a navigational perspective. Today we discovered that yesterday the sun moved from being north of us to south of us. I know this because my noon sight failed.

At local noon on each day of this passage I have propped myself in the companionway hatch with my sextant and prepared to take the day’s shot for latitude by facing north. I’ve been facing north for months–I am, after all, in the southern latitudes. But I’ve not been paying attention.

Today the reading I got was a nonsense. My sextant told me that the sun was 91 degrees, 45 minutes and 5 seconds above my horizon, and while this was more or less correct, it was not a number that could help me find my latitude.

The shot for latitude formula is shockingly simple. Given my location these last months, it’s gone like this:

90 degrees – corrected sextant reading = zenith distance.
zenith distance + sun’s declination on that day and hour = latitude.

I only need an external reference for two pieces of information: One, the exact time of noon where I am; two, the sun’s declination at that time. All this is conveniently stored in the NAUTICAL ALMANAC, a handy blue-bound book put together by the Brits, of which there is one aboard.

That’s it. Yes, there are a couple more wrinkles, but nothing to worry about here.

So, my work-up for yesterday, for example, looked like it has since I started doing this in Tahiti.

89 60 0 …that is, 90 degrees expressed in minutes, degrees, and seconds. minus
89.36.5 …my corrected sextant reading at local noon that day. equals
00.23.5
plus
04.28.7 …sun’s corrected declination for that day and hour from the NAUTICAL ALMANAC. equals
04.52.2 South Latitude, which was yesterday’s latitude at noon to within a mile.

But you will see that all this assumes my sextant reading is LESS than 90 degrees, against which today’s at 91*45’5 failed to cut the mustard. The formula had no idea what to do with it.

I had not realized that the sun and I were converging. Yes, I knew Murre was making quick northing, but I’d not noticed that the sun was moving south and was actually already below the equator. Yesterday’s declination of the sun at noon was exactly 23.5 miles north of our noon location. We’ve been averaging 5 knots an hour and most of it to the north, which means we were, as the old-time sailors used to day, *passing under the sun* at about 4:30 in the afternoon.

It didn’t even wave.

So, today’s latitude failed. That’s too bad. But on the bright side, I no longer have to fight Murre, who is heading northeast and so has been happily putting her sails in the way of my noon, north-facing sextant. Now I can face south.

Just this hour we hooked our first fish of the passage, a petite, two-meal fish with the shape of a tuna but the colorings of a dorado. It’s radiant in the sun, except that’s dead. And I must now cook it up. I hope you’ll excuse me.

end.

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