IOTA and the August 21st, 2017 Eclipse David W. Dunham International Occultation Timing Association (IOTA) Email dunham@starpower.net Cell phone 301-526-5590 IOTA Annual Meeting, Carson City, NV September 10, 2017

Unique opportunity to deploy greater resources than usual

The Solar Radius Although few are interested in observing near the edges, There has been increased interest lately in observatioms there The currently-used solar radius was determined in the late 19th century Observations by Xavier Jubier and others of the February annular eclipse in Patagonia showed a larger radius, and also gave more evidence for a bluish “mesosphere”. Xavier’s analysis with LOLA of my timings of the 1998 Feb. 26th total eclipse, from an island very close to the predicted northern limit, confirmed the 2017 February results (when I get a chance, I’ll digitize the VHS tapes of all of the observations of the 1998 eclipse and make them available). The newer solar radius means that the “true” limits are about 200m inside the limits calculated with the standard radius, which is way I defined the “graze zone” of interest to be centered 200m inside the predicted limits. The Kansas City Star ran a hyped-up story about how the limit predictions could be off by a half a mile, while on one side of a building, you could see the corona and totality for several seconds, while on the other, you would have only a deep partial eclipse, with no corona visible. In fact, the limits are not sharp. Across the km-wide graze zone, the corona is visible the whole time, but the equal brightness of the disappearing 2nd contact bead with the simultaneously reappearing 3rd contact bead varies from maybe ten times Venus on the outside to several seconds of totality on the inside. The solar radius is not sharp, and even at center, a visual observer can’t time the contacts to better than about a second.

Outline and Goals Continue IOTA’s long term solar radius measurements from eclipses Emphasis on edge observations, the ultimate grazing occultation How accurately can the path edges and solar radius be measured? Citizen science with many observers, this time with smart phones Co-located use of previous techniques (visual, telescopic projected image, filtered telescopic video) to estimate realistic accuracies –Not enough obs. Standardization of scopes, cameras, and filters, IOTA for the 2012 May annular eclipse and IOTA/ES since 2008 - Not enough observers Test color cameras and flash spectrum observations – most overexposed Re-reduce older observations with LRO lunar profile data (no longer limited to polar regions, so central timed recordings are useful) Desired Results: calibrate with Picard satellite & other solar radius data, and with methods used at previous central eclipses Some Results Obtained, not as many or as good as had been hoped. I won’t discuss past work, that has been covered in previous presentations at IOTA and solar eclipse conferences.

Citizen Science Eclipse Edge Determination There are several cities and towns that straddle the 2017 TSE path edges. IOTA wanted to mobilize people in those towns to observe the eclipse from many places, to say whether or not the eclipse happened, and if there is totality (last bead “completely” disappears, before another one reappears), time it as well as they can. In addition, we wanted observers to use smart phones, to video record the eclipse. IOTA finally set up a good Web page, at http://occultations.org/eclipse2017/ explaining how the observations could be made, but it was too little, too late, and almost totally ignored. The only media story that I am aware of, that resulted from this, was a historical article by a writer for space.com about the observations bracketing the southern limit of the 1925 total eclipse in New York City. Paul Maley’s advance efforts at Minden, NE were more productive.

The St. Louis Eclipse Expo, June 17, 2017 Aart Olsen and his wife travelled down from Urbana, IL to man an IOTA booth that I had paid for. Aart took two posters that Joan sent him, as well as many eclipse glasses and IOTA handouts. Local observer Wayne Clark helped some.

Advanced Observations I wanted to contact potential edge area observers and work with them the Sunday before the eclipse, to set up five “mighty-midi”-like 80mm refractors on mini-eq mounts, to record the eclipse With color Runcams from up to five stations across the predicted “graze zone”. But anybody interested enough in the eclipse to possibly do this wanted to observe closer to the center. Weather forced us to change location on Saturday, and during Sunday at the new location, was too late to make any arrangements, other than for our own observations.

Flash Spectrum Observations Recording the flash spectrum around 2nd and 3rd contacts promises good results, enabling measurement of the solar edge intensity profile in different wavelengths. But obtaining good-quality results of most interest, like the view at left and below, is quite difficult; I abandoned my attempt to do it, running out of time. Below: Flash Spectrum of 1980 Feb. 16th Total Solar Eclipse in Kenya

Calculating the Graze Zones I wanted to plot the edges of a zone, extending from 300m outside to 700m inside each Limit, on maps that we could post and send to potential observers. But this was not straight-forward. I used Xavier Zubier’s good interactive map at http://xjubier.free.fr/en/site_pages/solar_eclipses/TSE_2017_GoogleMapFull.html that allows one to calculate contact times accurately taking into account both lunar and terrestrial topography. Xavier had to give me advice about how to use his calculations to find the predicted limit, and I verified the calculation with Occult’s Baily bead observation calculation. But Xavier only plots the sealevel limit, although the point calculations are precise. So I had to zoom in on Xavier’s limit point at a given street, then do the same with Derek Breit’s eclipse map at http://www.poyntsource.com/New/Google/Total__Eclipse__of__2017_Aug_21.htm , and then change values for the two arbitrary offset lines that Geoff Hitchcock’s software generates, until one of them passed over Xavier’s limit point. Then I applied 0.3 km outside and 0.7 km inside to that “limit” value, which is then good enough to plot the graze zone quite accurately over an area where the height above sea level does not change by more than about 50m. I explained this procedure at http://occultations.org/eclipse2017/grazezone/ “Plotting the Graze Zone in Your Area”, but I think only a couple of IOTA observers used that page. I first used the technique to generate the northern-limit graze zone across St. Louis, for the eclipse expo that was held there in June. I checked Paul Maley’s calculations for Minden, NE, and Jan Kok’s for a road west of Wheatland, WY for his array of automated smart phones. During the week before the eclipse, I generated, and Steve Preston and Brad Timerson posted, graze zone plots across the Kansas City area, then Moberly, MO; s.w. corner of Iowa; Bowling Green, KY; and Oak Ridge, TN. I produced a few more mainly for my possible use, but there wasn’t time to post them.

Three Asteroidal occ’ns in central USA, Aug. 14 - 24   Three Asteroidal occ’ns in central USA, Aug. 14 - 24 Double star discovery – see Tony George’s presentation. But clouds chased us to Kentucky for the eclipse, too far east to go back to MO, so we just returned home Instead. We went to Columbia, MO, to be in Range of these 3 great asteroidal occ’ns Occ’n of 5.9-mag. SAO 59794 = HIP 34358 by 930 Westphalia on Aug. 14 at 9:25 UT = 4:25 am CDT – But clouded out along the whole US path Occultation of 9.0-mag. SAO 164213 = TYC 5780-00308-1 by 834 Burnhamia on Aug. 23 at 3.9h UT = Aug. 22 at 10.9 pm CDT Many Occultations Occur Between Solar Eclipses Below: These events provide 2011 July 19 occ’n of LQ Aquarii multiple dynamic location- by Binary Asteroid (90) Antiope tion-dependent opportun- ities for education and sci- ence. Help IOTA measure asteroids, stellar angular diameters, & discover & measure close double stars using your own, or a new sensitive cheap video ca- mera to capture data directly to your PC. Visit IOTA’s site at www.occultations.org for details. You should watch this composite video of the spectacular 2017 Mar. Aldebaran lunar graze in Mississauga, Ontario at https://vimeo.com/209854850 Occultation of 10.4-mag. TYC 0741-01184-1 by 849 Ara on Aug. 24 at 10:49 UT = 5:49 am CDT – the 2 obs. by others allowed a shape model fit. 11 David Dunham dunham@starpower.net cell 301-526-5590

During the rest of the talk, I’ll just describe as best I can the efforts to observe the eclipse near the path edges, that I know about, and about well-timed observations of Baily’s beads near center that I am aware of. Those of you in Carson City can give your own accounts.

Observations near northern limit About 100 people observed from the s.w. corner of Iowa, about 300m south of the south edge of the graze zone. But the video of the eclipse they obtained was compromised by variable thick clouds; a valiant effort, but nothing useful.

Observations near southern limit Left- Jan Kok’s setup to orient 21 Alcatel smart phones that automati- cally recored the eclipse. Even with the 8x telephoto, the corona and beads blended together, making it hard to tell even if any totality Occurred or not. Above, 31st St. in Minden, Nebraska, where 15 iPads were used to record the eclipse, but with results similar to Jan Kok’s.

Timed observations near the center Next total solar eclipses: 2019 July 2, n. Chile, n. Argentina 2020 Dec. 14, s. Chile, s. Argentina 2021 Dec. 4, Antarctica 2023 Apr. 20, W. Australia 2023 Oct. 14, Ore. to Texas, annular 2024 Apr. 8, N. America, see left