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» Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » Practice Sight: Critique of my Sun and Jupiter sight welcomed

Author Topic: Practice Sight: Critique of my Sun and Jupiter sight welcomed
Chris Faris

 - posted March 07, 2021 07:39 PM      Profile for Chris Faris           Edit/Delete Post 
Continuing my practice (and learning)...these are two practice sights from the Chicago area this morning, March 7. Actual GPS position was 41.566 degrees N and 87.380 degrees W. Based on my LOP plots for Jupiter (my first planet sight ever!) I came w/i ~2 nm of my actual position and for the sun ~9 nm (a long way off)...not sure what happened w/ the quality of the sight but Hs was 05.330 degrees...does this low angle contribute, or just a bad sight on my part? I welcome any critiques of my attached form and any pointers folks might have. I will post a moon sight in another entry. Thanks!

David Burch

 - posted March 07, 2021 08:31 PM      Profile for David Burch           Edit/Delete Post 
Very good. Keep up the good work.

Sights that low should be corrected for air temp and pressure. You can look that up if you did not record it.

Also it remains fundamentally important to not take just one sight each but at least 3, ideally 4 sights of each body. You can typically takes sights every 1 or 2 minutes counting time to read the dials, record the results and set up for the next.

From: Starpath, Seattle, WA
Chris Faris

 - posted March 08, 2021 07:01 AM      Profile for Chris Faris           Edit/Delete Post 
Thanks David...much appreciated. You triggered a couple of additional questions..."yes", Sunday was a bit odd as I could only see Jupiter for a short time and it was gone...I got two sights (but only worked the one). On Saturday, I did a bunch of sun shots, starting early (see the very low Hs) and did 12 sights for practice. My questions:
a) I've been spacing them out for no other reason than to let the sun get higher and to practice. I recall that >10 degrees Hs is preferred starting point. What should my pacing be? Every few minutes?

b) Once you have a bunch of sights, I was working just a couple of them, really based on which ones I felt were pretty good, and the higher angles? Should I be taking some type of average of a closely grouped set of sights? And how close should that grouping be? Every minute?

I'll re-view that section of the book, and I recall in the problems, it was stated for problems that "a set of sights was taken and this was the best one" or "the average was"...I need to refresh there.

My work sheet needs refinement, but is date, my exact GPS location, some bearings to some objects in the lake to help me practice there,then Hs and UCT (from my Garmin watch set to UCT)

David Burch

 - posted March 08, 2021 04:18 PM      Profile for David Burch           Edit/Delete Post 
a) 10 or 15º if you have the choice.

As for period, just do what comes naturally without rushing. This could be as short as every 1 or 2 minutes. The key is not the time, but be sure to give the micrometer drum a nice big turn before you start the next sight, so it is truly independent of the prior ones.

b) Review the section on fit-slope method in the book. also discussed with several more examples of real sights in the book Hawaii by Sextant.

If yhou get 4 or 5 sights in 10 or 15 min you will have a good scale for this. See also recent discussion of scales for plotting

From: Starpath, Seattle, WA

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