I have been toying around with an idea for the last few days, and this evening I tested it out.
Around astronomic twilight I set up my new style T-2 and lightbox on the back patio. I had previously checked my wristwatch against UT from the USNO and established the correction. I also laid in a small supply of suds.
So I sat down in a reclining patio chair and waited. I know a few of the brighter stars by heart, so when Deneb appeared around 9 pm, I knew I was looking slightly east of north. Venus happened to be passing just west of south, so I used the opportunity to focus the view and crosshairs. As I waited for a few more stars to appear so I could figure constellations, I sipped a cold one and was treated to a nice white meteor appearing in Draco and moving west.
A few minutes after 9pm I could barely see Polaris. I took a quick sight and computed it's azimuth on the laptop as 24 minutes east. I set that angle in the T-2 and set the vertical hair on Alpha Polaris. I then turned back to zero and dumped over and found to my consternation I was dead on line with my neighbors pine tree. So much for planning.
Well, I could see Antares and knew I had just minutes until it crossed the meridian, so I prayed.
And sure enough as I sighted it, it passed through a gap in the pine needles and I set the horizontal wire upon it. I glanced at my watch and began to count. After a few seconds I turned back to the T-2, still counting and watched as Antares approached and split the vertical wire as I adjusted the horizontal wire. I then checked the altitude and plugged it into the laptop and added the UT time I had counted as Antares crossed the wire.
And, well, I am a full 7 tenths of a degree off in Longitude. But only 2 tenths of a degree off in latitude.
Beer me!
Now, the point of the exercise, is that in order to compute one astronomical coordinate, you need a ballpark value for the other. So, a minor success on the first try.
P.S. According to google my latitude is 40.40 and my longitude 74.30.
You are way ahead of me on the equations, and maybe some day I'll work on catching up. I've done some solar and Polaris sights with decent results, using canned programs/ephemeris data (like Jerry Wahl's and SPADE) but have never tried other stars.
It is indeed a success to de it from scratch and have it come out anywhere close.
But it seems like with your methods you should eventually be able to get closer. The sea navigation books (e.g. Bowditch from 1960's) usually worked out values to tenths of an arc minute and hoped the final answers were within a minute under good contitions.
Refraction (not in your calculations?) would be a small number of minutes, and not the biggest part of the discrepancy.
I suspect there is some offset in the time scales that you haven't accounted for. When you are working "from scratch" aren't there things like leap seconds no longer being put into UTC, so UT1 drifts out of UTC, and 32.184 seconds (in 1958 definition) (and growing?) from TAI to TT and add dT to get UT1 (earth rotation time) and I got confused really fast at that point.
You sir, are a true 'surveying geek' and I applaud you for it. 🙂
This link is to a scan of the published transcription of the original Journal of Mason and Dixon by the American Philosophical Society. It has all their astronomical calculations.
Warning, huge file
Scott,
Interesting post, 10 million miles over my head, but very interesting nonetheless.
James,
Thanks for that link, I've downloaded the file and put it on my "nook". I never even thought about Mason and Dixon having a journal. I've read the Lewis and Clark journal several times and look forward to reading the Mason and Dixon journal.
It's not as "interesting reading" as Lewis and Clark.
More of a combination diary/field notes.
Hmm. The date is EDT and the time is UTC. Is that accounted for somewhere?
Making it 7/27 does wonders for the longitude, but of course the latitude didn't change much.
The neat part about this...
is that with just two angles and a little timing I came up with a useable astronomic coordinate.
The method makes no pretense to accuracy. It is by no means scientific - I could have used a couple of sticks, a plumb bob and ruler and attained the same accuracy.
The wonder of the method is that it does supply enough information to use in a more accurate observation and any surveyor can do it.
The neat part about this...
> The method makes no pretense to accuracy. It is by no means scientific - I could have used a couple of sticks, a plumb bob and ruler and attained the same accuracy.
I remember someone telling me a few decades ago, that what you mention was a question on the California PS state exhibit exam
Basically, how to find your position with the materials that you mention.
Essay question of course...
and Scott please put the [tex]minus[/tex] sign on your [tex]longitude[/tex],
I thought that maybe you had moved to Kyrgyzstan for a moment.
