I bought a cheap plastic sextant after reading some sailing books (The Long Way by Bernard Moitessier amongst others). I'm about as far away from the ocean as it's possible to get, though Lake Superior is right on my doorstep.
Anyway, I did some sun shots in the back yard with a plate full of Crisco for an artificial horizon - reasonable results for a novice i thought (around 10km off).
Last night it was a full moon, so out I went, spilling Crisco, trying to be quick before it filled up with bugs and obscured the sight - ran the numbers this morning - 4km off! I was well chuffed. I may have run aground in the real world, or sailed right past the harbour, but it's a start. Can't wait for fall and a chance to shoot some stars without staying up all night.
I'm doing a mixture of ancient and modern - using a sextant, but using Google Earth to plot my circles of equal altitude! And of course, I already know where I am...
The truth is, I signed up for a surveying diploma in the first place, mostly because it had a course in astronomical observations - and that very year, (2004) they dropped it for "GPS"! Bummer...
Anyone else play around with a sextant?
I've done a little, but I've had more interest in observing the moons of Jupiter to tell time. And last fall I took the astro workshop that NGS put on.
The moons of jupiter may have to wait 'til I'm a bit more experienced!
That Gallileo was a pretty smart guy.
When I was a younger whipper-snapper and starting out in Surveying I took an Adult Ed class in Celestial Navigation. Was also prompted by a previous acquisition of a WWII Lifeboat Sextant. Being reasonably proficient in calculating stuff I did pretty well.
There were 2-3 retired type guys in the class who were planning on going to Hawaii on their boat but were NOT proficient calculators. They asked me (no sailing experience) if I was interested in being the navigator on the boat. I declined but often wonder what a great experience that would have been.
(especially if they had a good looking, single daughter in line to inherit a large fortune)
Typically I would realize about the same accuracy you are seeing.
Marine Navigation is about getting within seeing distance of the destination then using your eyes.
I still have my HP-41 Astro ROM. Wrote a program to utilize some of the subroutines to do surveying Sun Shots for azimuth checks. Worked really well.
William F Buckley wrote a book about sailing in which he devoted several pages to his use of an HP-41 with a Celestial program to navigate across the Atlantic.
He may have had some influence on the creation of the HP Astro ROM.
Note: Once I did a Sun Shot with a Hewlett-Packard Total Station. Later I learned that you are not supposed to aim the thing directly at the Sun as it could burn out the EDM components inside. Boy, thought I was going to get in real trouble.
Don't know if this caution is still valid but you may want to check.
> Don't know if this caution is still valid but you may want to check.
Seeing as how most of the HP3820's are dead, it probably doesn't matter if you point one at the sun or not. But I, too, am of the understanding that EDM diodes are susceptible to damage from a direct solar pointing.
I navigated between New England and the Eastern Caribbean a few times before GPS using a sextant. The only electronics was a quartz clock and a radio direction finder. Sight reduction was with tables, paper and pencil. I shot the sun and the moon but never graduated to stars. I couldn't figure out which star was which. And you can only see both the star and the horizon for a very short time. A plate of Crisco doesn't work at sea.
Navigation and surveying have much in common.
Getting proficient with a sextant is very much like getting proficient with a transit, theodolite or TS.
Sight reduction and plotting a position is very much like closing a traverse.
Becoming an good navigator is very much like becoming a good surveyor. Navigation and surveying are both much more than calculation coordinates. The art of navigation includes preparing the vessel, the gear and the crew, and managing it all whatever happens. One big difference for me is that navigation is only for the satisfaction, not for pay, and also navigation is often a serious safety issue.
After a week or more at sea, telling the crew that our destination will appear on the horizon ahead in the next few hours is satisfying when you're right. Not too different from telling the crew that if they dig HERE, they should find the original stone. I sure do love it, though I admit to not using a sextant for 30 years.
Colin Frank-
4 Km with a plastic sextant is about as good as you can expect. But here's one place you should give up the metrics. 1 nautical mile is 1 minute of latitude or I minute of longitude at the equator or 4 seconds of time.
My first Celestial Navigation experience was in 1978 on the 72' yawl Royono. We left New England the day after Thanksgiving. Half way to Bermuda we drifted for 2 days in a gale and were lost. I had read about Celestial Navigation and, hey, I was a surveyor. So I got out the sextant. No one else on board had a clew. It turned out I subtracted instead of added a correction factor, but the course I plotted got us close enough to follow the lights of airplanes approaching Bermuda.
Great replies from all - thanks!
Yes I am a big fan of "Nautical" miles now - I only go to kilometres at the end when I do the ruler thing in Google Earth.
I am pretty certain you can't point a total station at the sun without a solar filter. I'm not going to try the bosses SRX without one that's for sure!
I find the sextant a very elegant tool, with the mirrors and bringing the object down to the horizon - no craning of the neck - and how it's a handheld instrument and yet so accurate - and that it works even when you are rolling up and down as everything is moving all at once....very clever indeed.
I'm getting a craving to find that sextant and go to the beach and play with it again.
Maybe some of the bikini clad ladies will assume I'm a rich old guy?
Never mind, probably less appealing than if I showed up with a metal detector looking of change.
