According to an NPR article this morning: In anticipation of possible GPS jamming, the Navy is providing training in celestial navigation.
Hope they keep non-GPS based clocks on board still. I guess I should have hung on to my filters and eyepieces for sunshots-
Always good to have a fall back plan if technology lets you down
I still have my filters and eye pieces, they just fit instruments that are sooo old.
Norm Larson, post: 359037, member: 7899 wrote: I still have my filters and eye pieces, they just fit instruments that are sooo old.
Yes, I had to do a sun shot a few years back and decided that I didn't need to use the robot so I took out the old T1-A and put the filter on it. I must say what a pleasure to use a mechanical instrument. Fine locks and tangent screws much more fun than telling the instrument to search or using a servo controlled tangent knob. Probably can't make a lot of $$ with the old instruments but the good ones were such a pleasure to use!!
Good question about non-GPS chronometers. Proper celestial nav would have to include all of the steps, including an approved time source.
Where does one find an ephemeris today? We used to get them for free at the local surveyor's supply store, but that was YEARS ago.
Andy
They need to bring back E-Loran. It is an important issue, not just for navigation but for timing as well.
But learning astro positioning techniques is a good idea.
Norm Larson, post: 359037, member: 7899 wrote: I still have my filters and eye pieces, they just fit instruments that are sooo old.
Filters and eyepieces? I still have the whole shooting match. Rolex GMT Master too.B-) 
Andy Bruner, post: 359073, member: 1123 wrote: Where does one find an ephemeris today? We used to get them for free at the local surveyor's supply store, but that was YEARS ago.
Andy
If you mean a paper book, I'm not sure, but you can get the MICA Ephemeris that works with both Windows and Mac, here:
I always meant to look into how a sextant worked as my mind has trouble getting around the pitch and yaw of a ship coming up with anything useful. i never have looked it up though
Norm Larson, post: 359083, member: 7899 wrote: I always meant to look into how a sextant worked as my mind has trouble getting around the pitch and yaw of a ship coming up with anything useful. i never have looked it up though
It's all a matter of perspective. They've never been as accurate as a 1 second total station...more like an old optical theodolite. But at sea, you don't need to know where you are within a tenth of a foot. With a reasonably good time piece, and a good triangular set of stars, a position fix within half a mile at sea would have been considered excellent in it's day. We didn't even use LSA, either...that probably would have improved things a lot, lol.
Often, though, you don't really need to know where you are as much as you need to know where you are relative to something else (like a reef, or a coast line). You can enhance the precision by choosing celestial objects that lie near the azimuth along which you'd like to know your position.
Finally, in a crossing, it's always comforting to know that every observation you make is pretty much inconsequential...except the last one you make before you make landfall.:-S
Thanks, so, once again my tendency to smash gnats with sledge hammers is an issue
Norm Larson, post: 359037, member: 7899 wrote: I still have my filters and eye pieces, they just fit instruments that are sooo old.
My filters used to fit over the objective lens of the old guns, now they fit inside the sun hood of the new guns.
Still gets the job done................
Wish they could update the ephemeris inside of my SMI v7
Here's a good almanac specifically for surveyors.
http://www.survplan.com/Star_Almanac_for_Land_Surveyors_2016.pdf
Norm Larson, post: 359083, member: 7899 wrote: I always meant to look into how a sextant worked as my mind has trouble getting around the pitch and yaw of a ship coming up with anything useful. i never have looked it up though
The reason it works even when it is moving around is that the operator is looking at 2 images at once, either split or superimposed, depending on the sextant. So the angle between the horizon and the sun, moon or stars stays very nearly constant.
[USER=8882]@rfc[/USER]
"I still have the whole shooting match. Rolex GMT Master too."
Please tell me you don't wear the GMT in the field daily! :woot:
Andy Bruner, post: 359073, member: 1123 wrote: Where does one find an ephemeris today? We used to get them for free at the local surveyor's supply store, but that was YEARS ago.
Andy
And of course, sun and Polaris in GHA, declination, in UT:
Jim in AZ, post: 359374, member: 249 wrote: Astronomical Almanac
What's nice about the Naval Observatory is that they have calcs and charts for all kinds of stars and planets, not just the sun. Even the moon.
MISSOURIMULE, post: 359676, member: 9473 wrote: What's nice about the Naval Observatory is that they have calcs and charts for all kinds of stars and planets, not just the sun. Even the moon.
This PDF is a compressive catalog designed for surveyors, (which is the same for sextant work); everything you wanted to know, but were afraid to ask:
The Star Almanac For Land Surveyors Her MajestyÛªs Almanac Office NP- 321 2016
http://www.survplan.com/Star_Almanac_for_Land_Surveyors_2016.pdf
650 stars, and sun, in Universal Time. Many star catalogs are in TDT (terrestrial dynamical time).
