A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Byron Franklin
Date: 2012 Oct 22, 09:11 -0700
Byron: This may be interesting to the Celestial new comer. many things in the books and schools are written and taught by people that have little sea time.
Mr. Brown “pass” Senior Editor for the oceanographic Office and Bowditch once told me. He was also talking about himself. I was underway at sea for most of any year, and was involved with navigating 100% of the time. I had no one to guide me that had more experience than me. Most of my experience and knowledge was on the job training. I did read a lot, and had the at sea time and equipment to learn & evaluate. After 1957 I never stood a Quartermaster watch, my duty was to stand 24 hour Navigation watch and trained the QM’s. At shore duty I taught Navy navigation curriculum at Officer’s Candidate School, I never seen or taught anything on how many stars to shoot or how many times for each star. I will talk about what I have observed personally. The time to get on the bridge to prepare for observing stars depends on sunrise/sunset. In the AM 30 to 40 minutes before sunrise. You want to accustom your eyes to the present light. You want to get the star/body as soon as the horizon is sharp to the east because the stars will start to fade. High stars away from the sun will pop out first & fade last. Don’t hurry, only get a few. Try to get a good spread. Soon the horizon to the west will sharpen and lower stars will stay sharp for a while. For sunset be ready 15 minutes after sunset. First look to the east because that horizon will thicken first. Look high darker blue with less atmosphere to see through, and to the east for the first star to appear, but still, look everywhere. You should in both cases sunrise/set have information from a star finder. High stars should start to appear first and early, get them with a good horizon. Don’t hurry. Try to get 4 or 5 with good spread. As in visual compass bearings you need to plot at least 3 ,best if two is near 90 degrees spread, the third any other angle but not parallel to judge the fix accuracy. Shooting stars is like shooting basket ball, the more practice the better, at first just shoot, (don’t concern with accuracy) after a while you know when the ball (star/ bodies) leaves you hand where the ball is heading or “good the shot”. More about spread. The Celestial, Line of Position (LOP) is a distance range from the Body; the same rules for shooting visual Navaid apply. 90 degrees is best to cut the running of sharp angles. Use at least 3 for judgment. (Two for fix, one for judgment. If the bodies are within 180 of each other, (example, Starboard side only) with error, you are outside the triangle. 100% of the time.
If the bodies spread are over 180 you are in the triangle. Some observer shoot in the water a little, thinking they are on the horizon. This makes the Height Observed greater and the Zenith Distance smaller. The range LOP is short of the observer. If the bodies are within 180 degrees and each falls short than, how could the observer ever be in the triangle? The same is true if the observer marks above the horizon! If bodies are more than 180 degrees than he/she is in the triangle. The same as Navaid LOP if the observer shoots two bodies near 180 degrees apart to the North & south and another two east & west with some error he will be in between the lines. This is a good check for your star placement.
The best time to shoot is when the horizon is sharp and the bodies are sharp, get out early stay late.
A good rule is observers twilight 10 degrees below the horizon. Nautical Twilight is in the Nautical Almanac at 12 degrees is good. Look at your Star finder and you can see that the length of time is not only how many degrees the sun is below the horizon, but your Latitude. And how the sun approaches the horizon at low latitudes the sun nearly goes down at 90 degrees, quickly. At high Latitudes the sun approaches the horizon at a slanted angle, giving more time for horizon and star time. I only shot 4 or 5 stars with the best horizon possible. In deep water with room a good fix is accuracy enough
yron: This may be interesting for the new comer in Celestial.
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com