Tuesday, December 05, 2017

DS occultations listed

I was still a little troubled that I wasn't seeing any Lunar Occultation events listed in OW. So I did a bit of digging.

At one point, I opened the regional double star file, NADoubles.txt, for North America. Wanted to see what was inside, if anything. Purportedly it is maintained by Mr Timerson. I was surprised to find a listing for the months of December and January, about two to three dozen each. But the star numbers didn't make any sense. Dec 1 noted "444cK6" and Dec 15 showed "2223SK0." These didn't look like SAO numbers. Was the ending bit hexadecimal? No... It looked like stellar class. Nothing came up in SkyTools.

The Dec 15 items caught my eye.
15 D 2223SK0
15 R 2223SK0

That date got me thinking so I fired up Stellarium and advanced the time rate. And after a while, Zuben Alkarab slid into view! An interesting triple star. Oh ho.

In SkyTools, I switched to the Special Events tab, activated the Two Bodies search, and looked for an occultation of the Moon and γ (gamma) Lib. Yes. Dec 15. Entry (or disappearance) at 9:59, mid-occultation at 10:36, and exit (or reappearance) at 11:17. Oh. Daylight. Maybe that's why it wasn't showing in Occult Watcher.

On a whim, initiated a Google search on 2223SK0. Got a hit. A page at the Lunar Occultations web site, showing the predictions for 2017 for Blue Springs Missiouri.
       day  Time     P   Star  Sp  Mag  Mag    % Elon Sun  Moon   CA   PA  VA  AA
 y   m  d  h  m   s       No  D     v    r V  ill     Alt Alt Az   o    o   o   o

17 Dec 15 14 27 57.6 d    2223SK0  3.9  3.4    6-  29   9 31 149 -88S 113 138 100
   R2223 = gamma Librae
      2223 is triple: Aa,Ab 4.0 4.2 0.10" 191.0, dT = +0.06sec : 
                      AB 4.0 11.2 43" 157.2, dT = +87sec
      2223 is a close double. Observations are highly desired
17 Dec 15 15 55 56.0 R    2223SK0  3.9  3.4    6-  29  20 36 174  87N 294 299 281
   R2223 = gamma Librae
      2223 is triple: Aa,Ab 4.0 4.2 0.10" 191.0, dT = +0.07sec : 
                      AB 4.0 11.2 43" 157.2, dT = +95sec
      2223 is a close double. Observations are highly desired

Coming together. But I still didn't understand exactly why some of these events were not showing in my candidate list.

Made a location in OW for Atlanta, Georgia that seemed better positioned. Nope. Still nothing.

Launched Occult to see if there was an issue there.

§

Occult shows the unusual star numbers. OK. Found some correlating information there. ZC and XZ lunar catalogs. Displayed a chart for the Moon with Zuben Alkarab. Tried to produce an animated GIF.

Changed the filter settings in OW and forced a sync. Ah ha!

Occult Watcher showing lunar occultations of double stars

At the bottom of the listing, the Lunar Occultation section appeared! So, at last, everything is working as required.

§

Learned that ZC is the zodiacal catalogue.

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