Celestial Navigation Qs. Simulated sights, long term almanac

[Adelie]

Trees:
What do you have for a sextant?
Timepieces?
What are you keeping them in?
Underway you need to practice a shot at least once per week hitting the MOB button on the GPS when you take the shot. That will give you feedback on how well you are doing.

[ohthetrees]

Originally Posted by Adelie

Trees:
What do you have for a sextant?
Timepieces?
What are you keeping them in?
Underway you need to practice a shot at least once per week hitting the MOB button on the GPS when you take the shot. That will give you feedback on how well you are doing.

I have a Davis Mark 3, the finest, cheapest sextant that money can buy! I have a pair of casio watches (known drift), keeping it all in a pelican case. I suppose I should consider a faraday pouch for the watches and calculators to protect from lighting damage.

[Adelie]

I have a 50cal ammo box that everything fits in. Waterproof too.
For a real Faraday you need an insulator around the items and inside the metal shell. Basically a 1 or 2 gallon ZipLoc I side the ammo box.

[SeanPatrick]

Originally Posted by hellosailor

Trees-
If you can find an old Palm for $25, you can also get Eveready Lithium AAA cells (with a reliable storage life of over ten years) to bag with it, and John Manson's Pilot Navigation app suite for it should still be around. (I checked, that's the correct author and program name.) Much smaller and more precise than packing almanac sets, probably would run for two months on two AAA cells, and of course, if you can find a motherload of old apps...it eliminates the opportunity to make a lot of simple math errors by doing all that for you.
There's probably an Android app that will do sight reductions, after all smartphones are much more powerful computers. Nice thing about the Palm is that like the Casio, it doesn't know how to display ads or ask you to join Facebook.(G)

There are [several] Android apps which do all the work for you - including plotting. "Celestial" by Navimatics is a popular choice. (I use it often.) Most of these apps don't require a network connection to run. With no connection, you will see no ads. In fact, you don't even need to have the phone registered with a cellular provider at all. As long as the app is installed, it will run.


Of course, you can't just pop a new set of AAA batteries into a cell phone to keep it running. But you can get phone chargers that run on batteries or that can be plugged in - or both. And I'd wager that it's a lot easier to get an old cell phone than a Palm. I actually have both - but only one Palm*, while I have multiple old cell phones. But ... you raise a good point: an old cell phone with a nav app is certainly a good item to have as a backup celestial computer.


*I think I do have the navigation app for the Palm that you mentioned. But my Palm is buggy and likes to shut off randomly so I don't think I ever even tried it out. One thing that would concern me is the accuracy of the app today. I suppose its values of Delta-T haven't been updated for quite some time. (These values are necessary to produce accurate ephemeris data.) The good thing about the Navimatics Android app is that it lets you use custom values for Delta-T, so even if you can't update it, it will still be useful.

[Gruz]

Originally Posted by ohthetrees

I have a Davis Mark 3, the finest, cheapest sextant that money can buy!.

You mean, the finest, cheapest PLASTIC sextant that money can buy.


Othervise, "the finest, cheapest SEXTANT that money can buy" would be Astra IIIB Sextant.

[Adelie]

For a backup kit the Davis-3 is the best bang for the buck. Accuracy of the D3 with appropriate averaging techniques is better than the 15 or 25 and approaches the accuracy of a decent metal sextant.

http://straitofmagellan.blogspot.com...tants.html?m=1

If you are doing CelNav professionally then an Astra-3B is going to be the best bang for the buck. Shots need to be quicker so you can get on with other duties and it allows you to shoot more quickly if you are weather limited.

For somebody that specifically wants a metal sextant for personal preferences then again the A3B is the best bang for the buck new. Used there are any number of really good sextants to be had on EBay for similar prices.

Tree:

Ha e you considered getting a mechanical timepiece? I have a Molija pocketwatch ($35 EBay) and a wristwatch if my father’s from I assume the ‘60s-‘80s. I haven’t determined error rate yet for either but I know they work.

If my Casios get fried I can rely on the mechanicals. If I’ve let them run down I can reestablish accurate time if from a known location or I can do a Letcher lunar to reestablish time to the nearest 30-60sec.

[Black Mate]

Originally Posted by SeanPatrick

There are [several] Android apps which do all the work for you - including plotting. "Celestial" by Navimatics is a popular choice. (I use it often.) Most of these apps don't require a network connection to run. With no connection, you will see no ads. In fact, you don't even need to have the phone registered with a cellular provider at all. As long as the app is installed, it will run.


Of course, you can't just pop a new set of AAA batteries into a cell phone to keep it running. But you can get phone chargers that run on batteries or that can be plugged in - or both. And I'd wager that it's a lot easier to get an old cell phone than a Palm. I actually have both - but only one Palm*, while I have multiple old cell phones. But ... you raise a good point: an old cell phone with a nav app is certainly a good item to have as a backup celestial computer.


*I think I do have the navigation app for the Palm that you mentioned. But my Palm is buggy and likes to shut off randomly so I don't think I ever even tried it out. One thing that would concern me is the accuracy of the app today. I suppose its values of Delta-T haven't been updated for quite some time. (These values are necessary to produce accurate ephemeris data.) The good thing about the Navimatics Android app is that it lets you use custom values for Delta-T, so even if you can't update it, it will still be useful.

I'm sorry to contradict you.
I Know and use almost all the software made with calculators up to the present day, but some CelNav for Android are not very accurate. One of them is Navimatics of which I have a license, and it works worse on iPad. Also Verified through the manual calculation. I recommend you always do a double check with something really reliable, like StarPilot, Astronav, Tamaya NC-77, Celesticomp V, etc.

[SeanPatrick]

Originally Posted by Black Mate

...some CelNav for Android are not very accurate. One of them is Navimatics [...] I recommend you always do a double check with something really reliable, like StarPilot, Astronav, Tamaya NC-77, Celesticomp V, etc.

Very interesting. Can you give an example which shows inaccurate data from the Navimatics app? It has been my experience that StarPilot is the least accurate of the calculators I have. (I have the TI-89 version.) The Navimatics app, as far as I have seen, has never disagreed with data from the USNO or Astronav (which also seems to be very accurate.)



Here is an example of data I get from various sources:


2019, March 29 12:00:00 UT
Moon GHA & Dec.


USNO website: 71°35.1' ; S21°23.7'
USNO MICA program: 71°35'05.652" ; S21°23'42.02"
Celestial by Navimatics: 71°35.1' ; S21°23.7'
Astronav: 71°35.1' ; S21°23.7'
Navigational Algorithms app: 71°35.1' ; S21°23.7'
StarPilot: 71°39.2' ; S21°28.4'


As you can see, all sources except StarPilot agree to within a tenth of a minute. I would be very interested to know what shortcomings you have found with the Navimatics app.

[Black Mate]

I have to agree with you on the StarPilot ephemeris. This is very strange!
However, when you go to the calculations, the StarPilot is excellent.
I invite you to solve this following exercise:

2019, March 29 08:00:00 UT
MOON (Lower Limb) - Ic= 1.4 (on) - e= 19 ft
DR (GPS) 40°55'.0 N - 009°31',6 E
Hs 26°29'.5

ASTRONAV = Zn 184°.2 - Intercept 0'.2 away
STARPILOT = Zn 184°.2 - Intercept 0'.2 away
NAVIMATICS = Zn 204° - Intercept 210.9 towards

Not a little mistake!
You can check the images from the following link.
I'm interested in your opinion, let me know.

https://www.dropbox.com/sh/eby0sfwii...xUXiUikra?dl=0

[Gruz]

Originally Posted by Black Mate

2019, March 29 08:00:00 UT
MOON (Lower Limb) - Ic= 1.4 (on) - e= 19 ft
DR (GPS) 40°55'.0 N - 009°31',6 E
Hs 26°29'.5

I think that something is wrong with this.

[Gruz]

NAVIMATICS = Zn 204° - Intercept 210.9 towards


navimatic is correct but still there is error in Hs reading.


For 29 March 2019, 08:00:00 UT

DR 40°55'.0 N
009°31',6 E

Moon (lower limb) Hs should be 22°57'.3 NOT Hs 26°29'.5





….and this is with correct sextant reading (hs)

[Gruz]

it would not let me edit so I have to add this...


ASTRONAV

STARPILOT


this two are more or less correct regarding intercept but Zn is wrong




NAVIMATICS = Zn 204° - Intercept 210.9 towards


navimatic is correct but still there is error in Hs reading, so it is also very wrong.

[Adelie]

There is a 30min limit on editing.

[Black Mate]

Sorry for the hurried conclusions. You are right.
I was doing two different simulations and I made a mistake.
I have reviewed the calculations, the value of Hs is 22°59'.5
Resetting the correct value manually :
Zn = 204°T - a = 0.9 nm away (Law of Cosines Method)
NAVASTRO : Zn = 203.5°T - a = 0.1 nm towards
STARPILOT : Zn = 203.6°T - a = 0.6 nm towards
NAVIMATICS: Zn = 204°T - a = 1.9 nm towards

Now if you like it, you can check it out.
Navimatics has always given me greater differences than Interceptor.
Probably as for StarPilot they have not adjusted the ephemeris, so even Navimatics have not updated it since 2015.
Navimatics on iPad is much worse.
Let me know what you think, thanks.

[Gruz]

"Let me know what you think, thanks."


I do not use any software, I am old school, paper and pen so not sure. It looks more or less ok, (couple of miles here and there), but I will still stick to my paper calculations just in case and I think that your HS is still wrong. 22°59'.5 it should be 22°57'.3



I just noticed that I made mistake in second calculation.

instead

22°51'.6
+ 0'.0
------------------
22°51'.0


should be 22°51'.06


Then Ho is 23°54'.4 NOT 23°53'.8 and intercept should be 1.4 M. away instead 2.8 away

Hc 23°55
- Ho 23°54'.4
---------------------
00°01.4