Introduction
The main purpose were accurate timings of the beginning and end of totality near the southern end of the moon's shadow and the determination of the southern umbral limit.
At the time there was still considerable uncertainty in the Moon's orbit and prediction of its position.
For the first time lunar limb corrections based on Watts chart profiles were applied among other improvements.
The Oregon State University expedition was stationed north of Madras, OR. More at 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, basically from visual observations with filter protection.
https://dermuehle.blogspot.com/2013/01/saros-120-eclipses19251979.html
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
https://dermuehle.blogspot.com/2024/11/baily-beads-analysis-for-solar-eclipse.html
Occult4 simulations for TSE 1979 in Oregon for my location "1+2640" 44.683883° N -121.127917° E 753m WGS84 yield
C2 = 16:13:58.0 UTC C3 = 16:14:16.0 UTC -> predicted totality duration = 18.0 sec
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| Lunar limb plots combined for 16:13:58.0 16:14:08.0 16:14:16.0 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 |
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 beads before C2 and first beads after C3
Discussion
Just after the beginning of totality there are three bluish-white spots in slide 19.
They can be understood as light from the solar mesosphere which has a pseudo-continuum spectrum of helium lines and low FIP (first ionization potential) elements.
After C3 there is s doublet of Baily's beads which is easily explained by the Occult simulation.
C3 is caused by the valley at PA 206, the valley at PA 196 is filled with sunlight immediately after C3.
Evaluation of totality timings
The procedure was to watch on a projection screen for the disappearence of the last bead before totality end 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 1 sec intervals. A new evaluation was done in 2024 using audacity, replay at half speed.
The results are
C2 = 08:14:00.0 UTC - coincident with the WWV beep
C3 = 08:14:18.9 UTC - is an upper limit, not allowing my personal reaction time
Thus totality duration = 19 sec rounded to the whole second.
