THE GREAT AMERICAN ECLIPSE
Total Solar Eclipse of 21 August 2017,
USA - Wyoming, Glendo Park, +4231'10.2" N, 10459'27.7" W, 1425 m a.s.l.
Local circumstances: C1 16.24.04, C2 17.45.08, max 17.46.22, C3 17.47.36, C4 19.12.15 UT, dur 2m28s
by Lorenzo Comolli

NOTE: here are some preliminary images and data of the eclipse; more will come in the next days/weeks
29/8: added AllSky images
11/9: added corona at 500mm
27/10: added corona at 150mm; flash spectrum processed by Berardi
28/10: added landscape and instrumentation images, prominences at C3


HDR Corona (at 500 mm)

Click for hires
The HDR corona in full details. Image collaboration joining the images from two nearly identical setup.
Two Pentax 75 refractor (500mm f.l. f/6.7), Canon 760D and 60D, two tracking mounts (Vixen GP and Kenko NES), exposures between 1/125 s and 1 s at 200 ISO, plus 1 s at 400 ISO. Nearly 100 total exposures were used.
This image is a collaboration between Emmanuele Sordini and Lorenzo Comolli.



HDR Corona (at 150 mm)

Click for hires.   Look at the same image superimposed to a Perseus map, with and without the star labels.
The HDR corona with a larger field of view, showing tens of stars in the field of Leo down to mag. 8.5. Image collaboration joining the images from two nearly identical setup.
Two Canon 100-400 lenses (used at 150mm f/8), two Canon 6D, two tracking mounts (Vixen GP and Kenko NES), exposures between 1/125 s and 2 s at 400 ISO, plus 2 s at 800 ISO. Nearly 130 total exposures were used.
This image is a collaboration between Emmanuele Sordini and Lorenzo Comolli.



Flash spectrum
The Flash Spectrum is the spectrum of the Chromosphere. This part of the atmosphere of the Sun has an emission spectra, on the contrary of the Photosphere with an absorpion spectra. The Chromospere is visible only for a few seconds at the C2 and C3 contacts. Thanks to the full spectrum sensitivity of the sensor, also emission lines up to 900 nm are recorded.

Images at C2, Canon EOS 450D modified full spectrum, 1/30s exposure, 400 ISO, RAW format, Tamron 18-270 at 270mm f/6.3 (actual f-ratio due to reticle: f/10), Star Analyzer 100 (31.8mm 100lpm reticle placed in front of the lens).
This image is a collaboration between Lorenzo Comolli and Emmanuele Sordini; processing Lorenzo Comolli.

A "professional" processing of the image at C2+1s, made by our friend Paolo Berardi. The maximum SNR has been obtained by curving the chromosphere and averaging. Moreover the continuum spectrum has been subtracted. In this way, tens of emission lines are clearly visible, especially the very faint iron lines (Fe).
Canon EOS 450D modified full spectrum, 1/30s exposure, 400 ISO, RAW format, Tamron 18-270 at 270mm f/6.3 (actual f-ratio due to reticle: f/10), Star Analyzer 100 (31.8mm 100lpm reticle placed in front of the lens).
This image is a collaboration between Lorenzo Comolli and Emmanuele Sordini; processing Paolo Berardi.
Images at C3
Image at C2+1s. A graph with identification shows the elements producing the lines up to 900 nm in the infrared.




Images at C2 and C3 at 3s intervals. The duration of the flash spectrum is very short, about 10 s.
Details of the processing by Paolo Berardi
Click for hires
Canon EOS 450D modified full spectrum, 1/30s exposure, 400 ISO, RAW format, Tamron 18-270 at 270mm f/6.3 (actual f-ratio due to reticle: f/10), Star Analyzer 100 (31.8mm 100lpm reticle placed in front of the lens)
.
This image is a collaboration between Lorenzo Comolli and Emmanuele Sordini; processing Lorenzo Comolli.




Prominences

Click for hires
Solar prominences just a second before C3, with also the chromosphere at maximum visibility. Extreme enlargment of the original frame.
Pentax 75 refractor (500mm f.l. f/6.7), Canon 60D, Kenko NES mount, 1/2000s exposure at 100 ISO. North at top-left.




All Sky during totality

Mouse over for labels. Click for hires with labels and without labels.
An All Sky shot gather all the sky in a single image, a very important feature when the time is limited like during a 2m28s totality! Four planets and four airplanes are visible, and also 24 stars.
HDR composition obtained at mid totality with a Canon 5D baader, Peleng 8mm f/5.6, exp 2.5s, 1/2s, 1/6s, 800ISO. Identification of stars made with superimposition of an all sky map generated with Perseus software.


Rectangular projection of the above all sky image. The orange/pink horizon is at 360. At left my telescope and binocular, and in the background the dome of the Millikin University. At right on the horizon the Bennett Hill in the Glendo National Park.



Environmental measurements
A solar eclipse greatly influences the Earth atmospere. The temperature, relative humidity, luminance and pressure data show typical trends, peculiar to each eclipse and location.
With a digital thermo-hygrometer I've measured a 9C fall of the temperature respect to the trend (comparison: 4C in Egipt 2006, 7C in Hungary 1999).
A digital luxmeter measured the horizontal luminance: this is a really interesting measurement, that show the tremendous fall of the light, between full Sun (125000 lux) and totality (only 3.7 lux, comparison: Egipt 2006 4.1 lux).
During totality I've measured the sky brightness with a SQM-L, obtaining 12.92 mag/arcsec^2.
Comparing this value to the SQM-LE database of Emmanuele Sordini, recording the sky continuously from his home near Varese, Italy, such a value is obtained during twilight when the Sun is at about 5.75 below horizon, i.e. at the civil twilight. Do you what to feel how dark is the sky during totality? Wait for the civil twilight, that is about 30 min after sunset!

Here are the plots of:
  • temperature
  • relative humidity
  • luminance





Landscape and instrumentation images

Click on the image for landscape and instrumentation images of the authors and telescopes.




Any comment about the images is highly appreciated, email me at comolli@libero.it


HTML Editing and Publishing by Lorenzo Comolli. Email me at comolli@libero.it.
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