Celestial correction for Great Lakes?

[kristjan]

The horizon of the lake is parallel to the horizon of the ocean, therefore the angle to celestial body is the same. Altitude for mariners is irrelevant. Barometric pressure corrections need to be applied, as most tables are meant for standard temperature and pressure.

[Smftdr2002]

Sean Patrick,

Oh right, thanks. I had the actual lat/long wrong trying to find it in this stream. Now I see the Google Earth. I'll redo it and see what I get. But I actually have to work now on news years eve : ( So later. It probably wont matter changing the DR that much so it looks like it is quite off. Maybe there was index error in the sextant after all.

Ken

[Gruz]

Originally Posted by Bigjim

Dip for all sightings was 12 feet or -3.4

IC is noted or zero if not.

Click on thumbnails to see larger images

Here is our Sun sight:




Here is our Moon sight:



Here is the Mars sight:

My sextant readings. same DR, same date, same hours.


Moon, 18 October 2018, 23:32:58 GMT

Sextant reading 24° 10'7

-------------------------


Mars, 18 October 2018, 23:36:18 GMT

Sextant reading 24° 30'7

---------------------------------------

Sun, 8 April 2018, 15:21:52 GMT

Sextant reading 41° 27'5



It looks that something is definitely wrong.

[Smftdr2002]

I recalculated in StarPilot using the correct position for the DR and as expected it doesnt change the answer. Still off by 20 miles to the northeast. So of no help. I like the plastic sextant/ index error or just plain error in the sights theory. The atmospherics aren't significant corrections. Based on your above info for Temp/pressure, the April Sun sight Hs correction is -0.1' and the October Moon/Mars sights have a 0.0' correction for the Hs. This from the A4 Table in the NA. I usually take several sights of the body and average them in some way.

[Gruz]

This is what I got.....

[Smftdr2002]

Guz,

Where did you get your Hs for the three bodies? They are new data, not on the pro formas. But you're using the same times. I haven't been following closely so wasn't aware there were other Hs to chose from. But exact same times? Curious.

You got a very close fix. And have solved the mystery. More accurate Hs's. All standard corrections, no special corrections needed. Nice

[SeanPatrick]

Originally Posted by Gruz

This is what I got.....

I'm not sure about some of the corrections you're making there*, but I ran your numbers through a reduction program and got a fix of 42°21.7' N, 87°49.7' W. That is only 0.36 nautical miles from your actual position. For three sights with an azimuth spread of only 30°, that is a phenomenal result! It's actually fantastic under any circumstances in terms of a fix using a sextant.

It also suggests that there is indeed some error which is particular to the OP's instrument or technique. The nature of that error still is (and will probably remain) a mystery.






*I'm assuming the 2.0' added to every sight is the index correction and the -3.0' is the dip correction (which should be -3.4'). I'm not sure about the addition of 0.1' to each sight, but I suppose that could be a systematic (personal) error correction. The other corrections should be as follows:

Mars
refraction: -2.1'; parallax in altitude: +0.2'

Moon
refraction: -2.2'; parallax in altitude: +49.6'; semi-diameter: +14.8'

Sun
refraction: -1.1'; semi-diameter: +16.0'


Looking back at my own working of the OP's data, I see I mistakenly used -1.7' for the refraction of the Sun instead of -1.1'. I had used a calculator to find the value which was displayed as -0°1'7.5806". I erroneously wrote this as -1.7'. Just another one of the many ways to make an error reducing sights.

[SeanPatrick]

Originally Posted by Smftdr2002

But exact same times? Curious.

I hadn't noticed that, but it is sort of odd isn't it?

[Gruz]

Originally Posted by SeanPatrick

*I'm assuming the 2.0' added to every sight is the index correction and the -3.0' is the dip correction (which should be -3.4'). I'm not sure about the addition of 0.1' to each sight, but I suppose that could be a systematic (personal) error correction.

Yes, you are correct.

I did not run thru all posts before starting calculations. I picked up just date, time & DR Lat, Long, so i improvised with my own IE & Dip and temperature and presure, so that 0'.1 that you are asking about is actualy temperature and pressure.



I should use this...…


Moon, 18 October 2018, 23:32:58 GMT Hs 24deg 13'.0


Mars, 18 October 2018, 23:36:18 GMT Hs 24deg 33'.0


Sun, 8 April 2018, 15:21:52 GMT Hs 41deg 29'.8




42:21.4 N

87:49.5 W

IE 0

Dip 3.4



On April 8, 2018 at about 10 am, the temperature was 31°F and the pressure was 29.30 inHg.

0'.0



On October 18, 2018 at about 6 pm, the temperature was 52°F and the pressure was 29.50 inHg.

0'.0

[Gruz]

Originally Posted by Smftdr2002

Guz,

Where did you get your Hs for the three bodies? They are new data, not on the pro formas. But you're using the same times. I haven't been following closely so wasn't aware there were other Hs to chose from. But exact same times? Curious.

You got a very close fix. And have solved the mystery. More accurate Hs's. All standard corrections, no special corrections needed. Nice

I am time traveler.



Try this one

Ford Island, Honolulu, Hawaii



Moon, 7 december 1941, 16:05:29 GMT Hs 50° 15'.7


Spica, 7 December 1941, 16:07:35 GMT Hs 38° 48'.8


Polaris, 7 December 1941, 16:09:41 GMT Hs 20° 43'.1



IE +2'.0


Dip -3'.0


74°F


inHg 29.95

[SeanPatrick]

Originally Posted by Gruz

I did not run thru all posts before starting calculations. I picked up just date, time & DR Lat, Long, so i improvised with my own IE & Dip and temperature and presure, so that 0'.1 that you are asking about is actualy temperature and pressure.

Are you saying you're just making up sights? If so, that's not helpful here. I could do that all day if I wanted. We're trying to help the OP figure out an actual problem.

[Gruz]

Originally Posted by SeanPatrick

Are you saying you're just making up sights? If so, that's not helpful here. I could do that all day if I wanted. We're trying to help the OP figure out an actual problem.

I did not "made up" any sight, I used his DR, his time and his heavenly bodies. I just did not check all posts so I did not have correct IE, Dip, pressure and temp, everything else is true, correct and by the book as you could/can see from your own calculations.
English is not my first language, and I know it is not perfect but no one have to be nuclear scientist to figure out what i am doing and writing about.

And i helped OP simply writing in one of my posts that there is NO special additional Dip corrections for great or any lakes, 10 or 600 ft. above sea level, just standard dip from almanac and that for beginning his sextant readings are completely wrong for particular date and time...




And I found interesting that OP disappeared, no more comments from him, so I am finished here and i will not post on and about this subject any more.

[Gruz]

Originally Posted by Smftdr2002

Guz,

Where did you get your Hs for the three bodies? They are new data, not on the pro formas. But you're using the same times. I haven't been following closely so wasn't aware there were other Hs to chose from. But exact same times? Curious.

You got a very close fix. And have solved the mystery. More accurate Hs's. All standard corrections, no special corrections needed. Nice

I have program that can give me/generate sextant readings anywhere in the world, any time (GMT) any date between 9999 BC to 9999 AD.

And Almanac within that program can be used to produce conventional Nautical Almanac pages for any date between 9999 BC to 9999 AD.



No mater what sextant readings OP have he is definitely wrong (no offend).