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+--- Thread: First time real horizon (/showthread.php?tid=158)
First time real horizon - BigBill - 07-21-2018
On July 7th we took a trip to the beach and I was able to use the natural horizon on Lake Michigan for a series of afternoon sun sights. This is the first time I've been able to use other than an artificial horizon or a bubble sextant. It was exciting to actually try it at last. I used a Davis Mark 3.
Good fun and the results were interesting.
I varied between upper and lower limb sightings, took six different sightings with multiple individual sights for each one. I threw out the sixth set of numbers because they were all over the place. They were taken in a rush and by then I was hot and tired.
The other five sets however I was able to work up. I had three sets that were basically the same, though the LOPs were all out about 8 nm to the west of my actual position. One set was dead on and a fifth set was about 10 nm east.
UL and LL didn't appear to make any difference, the set of three sights contained both.
I adjusted the mirror between each set of sights. I had only the horizon for this which I wasn't used to. When practicing at home I use a distant tree which I'm able to use to correct both horizontally and vertically. With the horizon all I could do was get things lined up one way and turn the sextant on its side to adjust the other way which is far more difficult. I'm assuming the errors were a combination of how my eye perceived the horizon and not getting the index correction quite right.
Hopefully I'll get another opportunity soon and can work on my technique more. Possibly I can nail down that elusive IC for this sextant.
RE: First time real horizon - pabrides - 07-22-2018
(07-21-2018, 03:43 PM)BigBill Wrote: On July 7th we took a trip to the beach and I was able to use the natural horizon on Lake Michigan for a series of afternoon sun sights. This is the first time I've been able to use other than an artificial horizon or a bubble sextant. It was exciting to actually try it at last. I used a Davis Mark 3.
Good fun and the results were interesting.
I varied between upper and lower limb sightings, took six different sightings with multiple individual sights for each one. I threw out the sixth set of numbers because they were all over the place. They were taken in a rush and by then I was hot and tired.
The other five sets however I was able to work up. I had three sets that were basically the same, though the LOPs were all out about 8 nm to the west of my actual position. One set was dead on and a fifth set was about 10 nm east.
UL and LL didn't appear to make any difference, the set of three sights contained both.
I adjusted the mirror between each set of sights. I had only the horizon for this which I wasn't used to. When practicing at home I use a distant tree which I'm able to use to correct both horizontally and vertically. With the horizon all I could do was get things lined up one way and turn the sextant on its side to adjust the other way which is far more difficult. I'm assuming the errors were a combination of how my eye perceived the horizon and not getting the index correction quite right.
Hopefully I'll get another opportunity soon and can work on my technique more. Possibly I can nail down that elusive IC for this sextant.
Bravo... Bigbill,
Many happy observations to come... :)
Human error is one adjustment only practice and persistence will cure. There is something called irradiation error and equation error that is unaccounted for in present reductions - thats why observers of old were VERY careful to observe accurately. Also with use of the MK 3 you haven't the benefit of a scope so naturally your observations will be more difficult. Please post some of your data in the CN challenge thread so we can all have fun working out your observations.... thanks
joe
RE: First time real horizon - EdCa - 07-25-2018
BigBill,
What a clever sextant the Mark 3 is! You weren't far off in your sights. They were close enough. Did you find the mirror moved a lot and that's why you needed to adjust it?
Did you bring along your bubble sextant?
Ed
RE: First time real horizon - BigBill - 07-26-2018
(07-25-2018, 09:15 PM)EdCa Wrote: BigBill,
What a clever sextant the Mark 3 is! You weren't far off in your sights. They were close enough. Did you find the mirror moved a lot and that's why you needed to adjust it?
Did you bring along your bubble sextant?
Ed
I was doing the adjustments before each set of sights just to make sure. It was a hot sunny day and I assumed they were needed. There was a little movement from set to set but not a whole lot. I was accompanying other people so I kept my gear minimal so only brought the MK 3. I haven't exactly nailed down a 'standard' IC for the sextant. Maybe once I've done that I can go back and refigure, who knows I might even get closer. Overall it was a good experience.
RE: First time real horizon - pabrides - 08-18-2018
After reducing your data Im thinking you were near Nordhouse dunes or maybe Ludington state park.... Google lat/long is not that reliable. Their map says your pos is in the middle of the township, but Im almost sure you were actually along the dunes..
joe
RE: First time real horizon - BigBill - 08-18-2018
(08-18-2018, 08:35 AM)pabrides Wrote: After reducing your data Im thinking you were near Nordhouse dunes or maybe Ludington state park.... Google lat/long is not that reliable. Their map says your pos is in the middle of the township, but Im almost sure you were actually along the dunes..
joe
Good work. We were in the State park along the shoreline about a half mile south of the official entrance. The LOPs run roughly parallel to the shoreline making it a difficult fix.