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shooting a star - stargazer - 12-24-2015
Here is something I remembered that may or may not be helpful.
When I was about ten years old I purchased a very cheap plastic sextant. I could never understand the "grownup" directions that came with it.
One evening I was standing facing the western horizon trying to aim at the horizon and pick up a star in the mirror. A cool Coast Guard guy came by and told me "Try doing it this way". He had his own "real" sextant that seemed to weigh 100 pounds. He showed me that if I held the sextant upside down and pointed the telescope at the star, it was easy to find the horizon in the mirror, couldn't miss.
OK, maybe everyone knows this, or maybe I remember it wrong, but that is the way I remember it. I'm old now so that was long ago.
For some reason I'm reading about celestial navigation and interested in learning the basics. Finally, after all this time! I've always navigated the mountains and wilderness using stars and moon and sun as a compass for direction only, but especially not for longitude. In the north, Polaris always shows your basic latitude with no tables or books. But longitude is difficult.
How do you all note the time to the second when operating alone? Glance at watch and subtract a second, then read the angle?
RE: shooting a star - Lipr - 12-24-2015
(12-24-2015, 02:24 AM)stargazer Wrote: How do you all note the time to the second when operating alone? Glance at watch and subtract a second, then read the angle?
Your CG taught method of finding the horizon is well known.
Yes, time is recorded first and then angle.
As to time recording; when shooting any celestial body I wear my $12 chronometer on my left wrist. At the immediate instance of the sight I count "1-2-3" at an interval equivalent to one second of time between the numbers. In that period of time here's what I've done;
At "1"- taken the sight- the body is on the horizon.
At "2"- lowered my sextant which hangs around my neck on a line of Dynema.
At "3"- Looked at my watch and noted the seconds of time and minutes of time. (in a few seconds from "3" I write the hours:minutes:seconds on an index card)
The counting of "1-2-3" spans a period of time of 2 seconds because I count "1" at the very instance of the sight. So, only two seconds must be subtracted from the time on my watch.
It's very easy and quite mechanical if you were watching me do it.
Some people use stop watches and start the stop watch at the instance of sight and then casually record the time based on the difference between elapsed time of the stop watch and the current time.
There was a stop watch, I don't remember the exact name of it...something like "911 stoptime", that when the button was pressed it froze the exact UTC time of the button pressing.
When recording the time I make no allowance from "CE"- chronometer error as my watch is always set to the correct UTC before any observations are made. So many books and sight reduction forms waste pages talking about CE and the need to note it. For me, it seems elementary and pointless to discuss it further than make sure your chronometer is correct BEFORE you take a sight and if it's not then know what the CE is and record the corrected time of sight when you make the sight.
But, with all of the concern for precise to-the-second" time, a 4 second error in time will only equal 1 nm error in position.
Larry
RE: shooting a star - stargazer - 12-24-2015
Thank you Lipr, excellent explanation! I like the counting and the support line. Starting the stop watch is a good idea, if you can hold both items and keep a thumb on the button. I hadn't thought of "starting" the stop watch, much simpler than "stopping" it and trying to figure that out, unless you have the fancy stopwatch you mentioned.
I wouldn't use dynema myself, or even para cord. I don't like anything that won't break with my body weight around my neck, rather lose my sextant than my head. I could carry a cheap backup sextant, but cheap plastic heads don't work very well. :-)
I suppose chronometer corrections should be applied below (on the boat) and the correct time applied to the watch/stop watch. In any event your idea of having the correct time is very sensible.
I'm happy to know I did remember that brief CG lesson correctly. Still lustful for his super nice "100 lb." sextant.
I intend to implement your ideas, but need to get a watch. My phone doesn't show seconds on digital and has no numerals on the analogue image, even though it has a second hand.
I sure miss seeing the sun around here!
RE: shooting a star - Lipr - 12-24-2015
I'll bet the CG sextant, even though you were young, was a bronze framed one.
Wouldn't that be nice to have?
You're right about the Dynema cord. Have you ever heard this one, "it won't happen to me"?
Personally, I despise any digital time display except as watch used for celnav.
The watch need not be anything fancy or expensive.
The stop watch that I couldn't remember the name of was "Sight Time" model 911" I can't find it anywhere so it mustn't be made anymore.
Oh well.
RE: shooting a star - stargazer - 12-27-2015
(12-24-2015, 04:27 PM)Lipr Wrote: I'll bet the CG sextant, even though you were young, was a bronze framed one.
Even though I'm old, I'm pretty sure when I was young it was after the "Bronze Age" started! So I don't imagine it was made of flint. :-)
Seriously though, I've seen a photo of a sextant made of ebony wood.
(12-24-2015, 04:27 PM)Lipr Wrote: Wouldn't that be nice to have?
Bronze would definitely be the ultimate frame. Drool! Bronze is much more corrosion resistant than even stainless steel in a salt water environment. Bronze apparently can last thousands of years outdoors without protection.
(12-24-2015, 04:27 PM)Lipr Wrote: The watch need not be anything fancy or expensive.
I've been thinking about the time keeper since your post. Quartz is the way to go for accuracy and dirt cheap. But what I was thinking is that on a boat, if struck by lightning and all electronics gone, digital clocks would likely go as well. I read many years ago about a fisherman on a lake in an aluminum boat with some type of metal fishing pole. His pole was hit by lightning. He survived, the bolt spiraled around the exterior of his body leaving a red track. His jacket zipper fused. His outboard motor was destroyed. So I don't think an electronic time keeper would survive, probably not even a watch.
I'm going with a cheap quartz, but will keep my eyes out for mechanical timekeepers just for fun when going out on the ocean.
(12-24-2015, 04:27 PM)Lipr Wrote: The stop watch that I couldn't remember the name of was "Sight Time" model 911" I can't find it anywhere so it mustn't be made anymore.
Good memory, and you are correct. None even on eBay, but I found a mention of it on a forum where the poster said he tried to get his modified and the company was no longer in business. GPS ended his business I'd guess. I'm thinking a stopwatch simply adds more complexity to the equation, I like your counting method better. Simple and pure.
I'm going to get a good sextant soon. The navy has begun teaching celestial navigation again (this year) because the sun, moon, and stars cannot be hacked by cyber warfare. So the demand and price of good instruments will likely begin to rise. This may be the sweet spot in time to acquire one.
RE: shooting a star - Lipr - 12-28-2015
(12-27-2015, 01:09 PM)stargazer Wrote: LiprThe stop watch that I couldn't remember the name of was "Sight Time" model 911" I can't find it anywhere so it mustn't be made anymore.
I was looking for similar stopwatches and found that the words I needed to look up are "freeze time of day" stopwatch.
This site might be selling a similar sort of stopwatch;
Freeze time of day
Mechanical watches are a good a idea. When you look at the watch you remember "a picture of the time", so to speak. That might be better than digital?
Isn't that the way it is- the Naval academy (govt.) starts something new (celnav) and the price of an item (sextant) goes up! At least there will be more parts available for whatever make and model they expect the students to purchase.
Finally the Sun has come out after many days. Time to take a Sun sight.
Larry
RE: shooting a star - c_davidson - 12-31-2015
(12-28-2015, 01:30 PM)Lipr Wrote:(12-27-2015, 01:09 PM)stargazer Wrote: LiprThe stop watch that I couldn't remember the name of was "Sight Time" model 911" I can't find it anywhere so it mustn't be made anymore.
I was looking for similar stopwatches and found that the words I needed to look up are "freeze time..
The Fastime 14 will freeze the time of day a sight was taken. It's $64.
![[Image: 52_0_l.png]](http://www.astopwatch.com/content/products/52_0_l.png)
Freeze Time of Day