Introduction
The main purpose were accurate timings of the beginning and end of totality near the southern edge of the Moon's shadow and the determination of the actual southern umbral limit.
At the time there was still considerable uncertainty in the computation of the Moon's position. For the first time lunar limb corrections based on Watts chart profiles were applied among other improvements. The expected accuracy was 0.2 arcsec, it turned out to be 0.5 arcsec. The Oregon State University expedition was positioned north of Madras, OR. More in my blog post from 2012
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| A success: The O.S.U. Solar Eclipse Expedition to Madras, Oregon |
Three Saros cyles before in 1925 there had been a similar endeavour from Manhattan from purely visual observations.
The data for the moon's position and its shape has reached a level of precision which allows for the determination of the photospheric solar radius from observations in the graze zone just inside the umbra. Crucial are the data from the Lunar Orbiter Laser Altimeter (LOLA) on NASA's Lunar Reconnaissance Orbiter (LRO). They are used by the module "Baily Bead Analysis" in the Occult software by David Herald. See my evaluation for the total eclipse in Texas 2024 with a comparison of the results by the Besselian Elements team .
Occult4 simulations for TSE 1979 in Oregon for my location "1+2640" 44.683883° N -121.127917° E 753m WGS84 yield
C2 = 16:13:58.7 UTC C3 = 16:14:16.2 UTC -> predicted totality duration = 17.5 sec
Plots bracketing C2 and C3 were done at 0.1 sec intervals. I estimate the error in the predicted contact times +-0.1 sec each.
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| Occult lunar limb plot for C2 16:13:58.7 |
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| Occult lunar limb plot for 16:14:16.2 UTC |
Digitized slides from Kodak Ektachrome 400 f=270mm
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| slide 18 14:13:52.9 UTC |
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| slide 19 14:14:01.7 UTC |
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| slide 20 14:14:20.9 |
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| Click for animation from slides 18,19,20 |
Baily's beads analysis
The images from slides 18, 19, 20 are plotted with the limb profiles from Xavier Jubier based on Kaguya data and Occult. The lunar limb profile matches with the last bead before C2 and first beads after C3. C3' is not correct in Jubier's graph which is based on the Kaguya profile.
Discussion
Baily's Beads
Just after the beginning of totality there are three whitish spots in slide 19 at the valleys PA 171.0, 175.2, 176.9. They might stem from the elusive solar mesosphere which emits a pseudo-continuum spectrum of mostly helium emission lines. More in the appendix.
After C3 there is s doublet of Baily's beads which is readily seen in the Occult simulation.
C3 is caused by the valley at PA 206, the valley at PA 196 is filled with sunlight immediately after C3. On the tape I recorded "diamond again" 1.4 sec after "see diamond" at C3.
Evaluation of totality timings
The procedure was to watch on a projection screen for the disappearence of the last bead before totality and the appearence of the first bead after totality. Comments and the WWV time signals on shortwave radio were recorded on cassette tape. The tape was digitized and calibrated against the WWV beeps at 1 sec intervals. A new evaluation was done in 2024 using Audacity, replayed at half speed. See the annotated transcript in the appendix.
The results are
C2 = 08:14:00.3 UTC - almost coincident with the WWV beep
C3 = 08:14:18.9 UTC - is an upper limit including my personal reaction time
Observed totality duration = 18.6 seconds.
While the disapperance of the last bead at C2 came as anticipated, the first bead at C3 came naturally as a surprise, so an observed totality duration = 18.5 seconds might be a better value.
Occult simulations with the solar radius reduced by deltaR yield predicted totality durations
18.2 sec for deltaR -0.05" and 18.7 sec for deltaR -0.1".
Simulation with enlarged solar radius
A correction of + 0.32" was applied in Occult. The enlarged value 959.95" has been popular for more than 10 years for eclipse predictions.The stacked limb plots are for UTC 16:14:00.0/00.5/08.0/12.0/13.0.
Predicted totality = 12 sec.
Before C2 there would be a double bead at PA 171.0 and 176.9.
C3 would occur at PA 196, not 206 as observed.
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| Limb plots for UTC 16:14:00.0/00.5/08.0/12.0/13.0 with enlarged solar radius + 0.32" |
Summary
Based on the Baily Bead analysis in Occult 4 a rather good reconstruction of the TSE of Feb. 26, 1979 from the southern graze zone in Oregon at my site 1+2640 is achieved using the standard solar radius 959.63".
Differences remain:
The predicted duration of totality is 17.5 sec vs. ca. 18.6 sec observed from my location at site 1+2640.
The predicted time for C2 is 1.6 sec early compared to observation.
The predicted time for C3 is 2.7 sec early compared to observation.
Hints of the elusive solar mesosphere were imaged on a slide taken at f=270mm focal length.
Shadow bands were readily seen visually but did not show up on b/w photos.
The slides by Robert Dale Hall using an 8" f/10 Criterion Schmidt/Cassegrain from site 1+5280 are also consistent with the standard solar radius 959.63". The enlarged value 959.95" in Occult just does not fit.
In hindsight it's hard not to overlook the solar mesosphere in his images.
Images through a Criterion Dynamax 8 telescope
f=2000mm by Robert Dale Hall and comparison with Occult moon limb profile
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| last bead before C2 |
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| first bead after C3 |
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| partial phase after C3 |
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| C2 and Occult profile |
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| C3 and Occult profile |
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| C2+C3 and Jubier profile |
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| C2 C3 and Jubier profile |
Appendix
Annotated tape transcript
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| Annotated tape transcript |
Literature
Solar radius determination
Published corrections delta-r to standard solar radius r=959.63"
+0.08" +- 0.09 Dunham 1980
-0.11" +- 0.05 Fiala et. al. 1994
-0.05" +- 0.08 Dunham 2010
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| Dunham 1980 |
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| Sofia et. al. 1980 |
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| Sofia et. al. 1980 |
Solar Radius Variations Measured in Central Eclipses
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| Sigismondi 2008 |
https://www.icranet.org/download/ESOP/Slides/dunham0.pdf
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| Dunham 2010 |
Solar mesosphere
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| Sigismondi et. al. 2012 |
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| Bazin, Koutchmy 2013 |
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| Bazin et. al. 2014 |
