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Re: Occultations of stars by the Moon
From: Geoff Hitchcox
Date: 2023 Oct 20, 03:44 -0700

Bonjour Kermit,

I first noticed the "Swiss Ephemeris" (hereafter "SWE") a few years ago, but stayed away because it is driven essentially by the Astrology industry.

However, on reflection, I reasoned that many of the early Astronomers kept themselves solvent (capable of meeting financial obligations) by selling Astrological advice to wealthy patrons - by reading their *fortunes* - so the astronomers could carry on with their passion.

My present view about SWE is that it is an impressive work, and is still actively maintained, and a wonderful FREE resource to those of us who like to tinker with code - they also have a license for commercial use (which is not my interest). The developers are very keen that it delivers "accurate" position data (we will overlook the Astrology) and I have found it interesting to play with. It can generate huge long outputs of scenarios.

It takes a bit of getting used to all the options it has - but on the other hand, it is very powerful.

I compiled it to run on my LINUX computers, however there is an online version that if you paste the following line into the box labelled "other options" (and leave the other input boxes as they are) and then click SUBMIT

-ejpl -occult -pf -b01.01.1924 -local -xfRegulus -geopos288.408833,41.845167,107

It will go search for the Occultation that Frank mentioned (with the star REGULUS), the output should look like this:

==============================================

total(sunrise)   23.10.1924	  11:34:29.2	1.000000	2424081.982282
	73 min 31.58 sec	  10:58:01.6    10:58:01.6    12:11:33.2    12:11:33.2  dt=23.7

==============================================

output 1st line: eclipse date, time of maximum, eclipse magnitudes, Julian day number (6-digit fraction) of maximum

output 2nd line: local eclipse duration for totality (zero with partial occultations), local four contacts,delta t in sec

Occultations with the remark "(daytime)" cannot be observed because they are taking place by daylight. Occultations with the remark "(sunrise)" or "(sunset)" can be observed only partly because part of them takes place in daylight.

==============================================

You asked if it can do "No Refraction" Kermit, and the answer is only for Rise and Set commands, not Occultations.

As an example, to calculate the time of Sunrise on the 23.10.1924 using this set of commands:

-ejpl -b23.10.1924 -n1 -s1 -geopos288.408833,41.845167,107 -p0 -rise

It should report:

==============================================

rise     23.10.1924	  11:07:45.4    set      23.10.1924	  21:53:06.5    dt =  10:45:21.0

==============================================

If we now use the -norefrac option:

-ejpl -norefrac -b23.10.1924 -n1 -s1 -geopos288.408833,41.845167,107 -p0 -rise

we get:

==============================================

rise     23.10.1924	  11:10:52.2    set      23.10.1924	  21:49:59.8    dt =  10:39:07.6

==============================================

Kermit, in my last message I used the term "Occult", which I can see is ambiguous. I didn't mean the Windows EXE program called OCCULT written by Dave Herald (in IOTA), I just meant the -occult option in SWE.

Regards, Geoff Hitchcox, Christchurch, New Zealand (a little bit smaller than France ;-)

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