A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2021 Mar 2, 00:16 -0800
Joshua Hunley wrote:
"I ran across a technique for calculating GHA Aries requiring only simple arithmetic and knowledge of its value at 0000UT on 31 Dec (alternately, 0000UT 1 Jan)."
That is the same technique I use to calculate Julian dates. I have a small piece of paper on which is written the JDs for the "zeroth" day of each year (as you wrote: really just Dec. 31st of the previous year). I simply add to that the number of days that have passed since then and Bob's your uncle.
And, coincidentally, over the past week I have been reverse engineering Table 4 from Pub. 249. This is the table that allows one to calculate the GHA and dec. of the Sun over a 35 year period using just two pages. The good news is that I successfully recalculated all of the tables for the years 2021 - 2056 (as opposed to 2001 - 2036, which is the last set I have). The bad news is that was pretty much a waste of time, because all one has to do is swap out the years in the old table. All of the cyclic corrections line up just fine and the table works as well as it did before.
Anyway, point is: those tables use the same process, too. You basically start with the position at 00UT and add increments for the time of observation. It was a nice surprise to see your post today, because my next task is to recreate the GHA Aries tables to use with the "Q correction" tables for Polaris (which I have already finished). All of that is going into a booklet which I hope to make available soon. But I was sure I had seen a simple formula for calculating GHA Aries ... I just couldn't remember where (still can't). So, thank you for posting this. I was thinking about including such a formula in the notes/instructions.
Also, Frank wrote:
"Have you tried the new capability in the Lunars Analysis/Clearing app?"
Coincidentally, yes I have. And I did notice the changes. Nice job! Just last night I was shooting a few lunars ... the first ones I have done in a very long time. I have been quite busy working on my almanac and other projects, so actually getting out and playing around has taken a back seat. But I was compelled to get back to it by the arrival of my new sextant!
Some of you might remember Glen Swanson mentioning last month that he had three Tamayas and was thinking about getting rid of one to make room for a different type. I mentioned that I had wanted a Tamaya for a while and he told me to contact him privately. Well, we were able to work out a deal and I am now the proud new owner of a well-cared-for 1989 vintage Tamaya MS-633. I had never heard of this particular model, but it seems to be almost identical to the Spica/Jupiter except for the design of the frame. It was performing very well right out of the box (I.E. 2' off the arc). It did need some very minor TLC here and there, but the first lunar I shot was only off by 0.4'.
Anyway, I was equally surprised to see your post about this today, Frank. I didn't try anything "exotic", but I did shoot a couple Arcturus lunars, which - AFAIK - is not a "traditional" lunar choice. But thanks for expanding the selection! As you can see, your app is my "go-to" when I want to shoot some quick lunars for fun or test the sextant or myself.
Then there's Jim's post about a celnav simulator only a few weeks after I post a poll about the same thing in another forum. Seems to me there are a lot of coincidences around here lately. Either that, or it's just a feedback loop from spending so much time thinking about celestial stuff. Probably the latter.