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Total Solar Eclipse of 8 April 2024 USA - Arkansas, Nimrod Lake, +34°57'50.7" N, 93°12'35.8" W, 80 m a.s.l. Local circumstances: C1 17.32.30, C2 18.49.31, max 18.51.39, C3 18.53.47, C4 20.10.24 UT, dur 4m17s by Lorenzo Comolli, Emmanuele Sordini, Alessandro Gambaro |
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| The
HDR corona from the TEC140+ASI6200MM setup. A great
quantity of fine details is visible all along the
corona. Prominences were added from C2 and C3
contacts, red coloured. Moon edge is clearly oval due
to the long duration of this eclipse (more than 4
min), and during the image acquisition the Moon moved.
This is the biggest setup of our eclipse expedition
and it was extremely difficult to take this setup from
Italy. The telescope has beed dismounted in 3 pieces
and two big suitcases were necessary for
transportation via airplane. The camera is a ASI6200MM, a full frame of 61 Mpix 16 bit monochrome, and it was a first time for us uf using an astronomical camera instead of a reflex camera. This was possible thanks to the big improvement in download speeds of modern camera, e.g. this big frame sensor is downloaded to PC in less than half a second! TEC140 apochromatic refractor (dia 140 mm, FL 1011 mm, f/7.2), ASI 6200 MM camera (CMOS full frame 62 Mpix, 16 bit monochromatic, binning 1, 3.76 um/pixel, cooling at 0°C), ZWO AM5 mount, Luminance filter, exposures between 1 ms and 512 ms at 1 EV stops at gain 100 (equivalent to 680 ISO, EV stops from 15.9 to 3.9), 381 frames used summing for a total of 52.2 s of net exposure captured during 187 s of gross duration. Image capture via an automated sequence in SharpCap recording data at 2 fps with a data flux of 242 MB/s into a SER file. Image processing by Lorenzo Comolli. Image setup controlled by Lorenzo Comolli. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
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| Rectangular
projection of the above image. The radial structures
can be appreciated in a different prospective. Image processing by Lorenzo Comolli. Image setup controlled by Lorenzo Comolli. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
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| The HDR
corona with medium field of view. Obtained with a
"standard" setup, i.e. a Canon reflex camera, while
mosto of the other images from this expedition where
obtained with astronomical CMOS cameras (like the
ASI6200MM above). The difference in the noise and
details is quite noticeable. Pentax 75 apochromatic refractor (FL=500 mm, dia 75mm f/6.7), Canon 90D (32 Mpix, RAW files), Kenko NES mount, exposures between 1/250 s and 1 s at 200 ISO, plus 1 s at 400 ISO. 177 total exposures were used. Image processing by Lorenzo Comolli. Image setup controlled by Emmanuele Sordini. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
| The Flash
Spectrum is the spectrum of the Chromosphere during the
very few seconds after C2 and before C3. 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, so this is the reason
for the name "flash". We used a monochrome sensor
without filters, gaining the full spectral sensitivy of
the sensor from 330 nm to 1000 nm. The colors in the
images below are pseudo-real colors, added to the BW
original image. |
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| Images
at C2 (above) and C3 (below), QHY5III-174 camera
(1920x1200 pix, 5.86 um, 12 bit monochrome, gain 0
equivalent to 672 ISO, USB 3.0, 77 fps i.e. 338 MB/s of
data flux), optics made with a Atik 0.5x doubled (FL=100
mm, dia 25 mm, f/4), Star Analyzer 200 reticle (31.8 mm
200 lpm reticle placed in front of the lens), 13 ms
exposure, each of the two above is an average of 800
frames from C2+0s to C2+10s and from C3-10s to C3+0s.
The spectrum is strongly defocused in the left and right
regions becase unfortunately we forgot to add a
diaphragm designed to close the optics to f/9 so to
improve optical quality. Image processing by Lorenzo Comolli. Image setup controlled by Emmanuele Sordini e prepared by Lorenzo Comolli. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
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| A
"professional" processing of the data at C2, made by our
friend Paolo Berardi. The maximum SNR has been obtained
by curving the chromosphere and vertical averaging the
lines. Moreover the continuum spectrum has been
subtracted. In this way, tens of emission lines are
clearly visible. See above for tech data. Image analysis by Paolo Berardi. Image setup controlled by Emmanuele Sordini e prepared by Lorenzo Comolli. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
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| Solar
prominences at the C2 and C2 contacts from the TEC140
setup, with also the chromosphere at maximum visibility.
Rectangular projection, so the circular profile is
converted in a straight image. Look at the hires image
for full details and scroll left-right the image at 100%
resolution. TEC140 refractor (1011mm f/7.2), ASI6200MM, ZWO AM5 mount, 0.39 ms exposure at gain 0 (equivalent tot 215 ISO, EV=15.9), average of 23 images per contact, processing with Autostakkert 3 and Registax 6. Image processing by Lorenzo Comolli. Image setup controlled by Lorenzo Comolli. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
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| Sequence of C2 and C3
contacs at 4.1 fps from the TEC140 setup. 25 images per
side show a total duration of 6 s per side. The very
fast change in the solar appearance is clearly
appreciable expecially in the high resolution version. TEC140 refractor (1011mm f/7.2), ASI6200MM, ZWO AM5 mount, 0.39 ms exposure at gain 0 (equivalent tot 215 ISO, EV=15.9), image capture at 4.1 fps. Image processing by Lorenzo Comolli. Image setup controlled by Lorenzo Comolli. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
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| Sequence of C2 and C3
contacs from the Pentax75+Canon90D setup. 20 images per
side show a total duration of 12-10 s per side.
Unfortunately the continuous shooting of the reflex
camera was not at a constant framerate as the TEC140
setup. Pentax 75 refractor (500 mm f/6.7), Canon 90D, Kenko NES mount, 1/2000 s exposure at 100 ISO. Image processing by Lorenzo Comolli. Image setup controlled by Emmanuele Sordini. This image is a collaboration between Lorenzo Comolli, Emmanuele Sordini and Alessandro Gambaro. |
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| Sequence of
the full eclipse from C1 to C4 on a single image at 3
min intervals. This is a classic goal for eclipse
astrophotograpy, that at the time of film photography
was obtained on a single film piece, and now with
digital imaging is obtained from many shots added
together via software BUT with the requirement that
pointing of the camera is maintened fixed. Sequence obtained with a Canon 6D baader, Canon 50 mm f/1.8 used at f/5.6, exp 1/30 s during partiality (with solar filter) and 0.25 s during totality (without filter), 100 ISO, 3 min intervals. The last 6 frames were digitally added because pointing of the camera was not perfect and the Sun went outside of the field. |
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| The authors in
a group photo taken during totality. This was a goal of
our expedition, something to take with us in the future
as a reminder of the expedition. Taken near mid
totality, with the eclipsed sun at the top, with Venus
on the bottom right, the double setup of Alessandro on
the left (Pentax75 and EDPH61), the authors in the
middle (from left Emmanuele, Alessandro, Lorenzo), on
the right the setup of Lorenzo (TEC140) and at extreme
right part of our car with engine on for powering all
the instrumentations and PC. Also a buffer car battery
(in the middle bottom) is present. Btw powering all our
setup was very difficult because we found many
unexpected problems caused by the long time under the
Sun before the eclipse, heating all the PC and mounts. HDR composition obtained at mid totality with a Canon 6Dmk2, Samyang 14 mm f/5.6, exp 2.5s, 0.66 s, 1/6s, 800ISO. |
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| An All Sky
shot gather all the sky in a single image, a very
important feature when the time is limited like during
an eclipse totality! HDR composition obtained near mid totality with a Canon 6D, Peleng 8mm f/5.6, exp 4s, 1s, 1/4s, 800ISO. |
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| Rectangular projection
of the above all sky image. The orange/pink horizon is
at 360° but it is visible only in a small part of
the horizon due to the trees. At left the telescope
setups and authors while taking the group photo (see
below). |
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A solar
eclipse greatly influences the Earth atmospere. The
temperature, relative humidity, luminance data show
typical trends, peculiar to each eclipse and location.
During this eclipse I've used a T/RH datalogger with the sensors positioned at 1 m heigth on a small tree, on the side in shadow from the Sun light. This way data are quite reliable and much less influenced by the ground temperature respect to the measurements I've made in the past eclipses. In this eclipse I've found a 5°C decrease, to be compared to 9°C in 2017 USA Wyoming, to 4°C in 2006 Egypt, to 7°C in 1999 Hungary. A digital luxmeter measured the horizontal luminance: this is a really interesting measurement, that show the tremendous fall of the light, between full Sun at 110000 lux and totality at only 1.8 lux, to be compared to 3.4 lux 2017 USA Wyoming, 4.1 lux 2006 Egypt. The lower value, in my opinion, is due to 2 reasons: first the eclipse was quite long and deep (as confirmed by the SQM reading below), and second the selected location was surrounded by many trees, reducing the ambient light coming from the horizon. During totality I've measured the sky brightness with a SQM-L, obtaining 13.56 mag/arcsec^2, that is equivalent to the twilight sky when the Sun altitude is -6°C, i.e. 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:
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 Click for the PDF presentation |
| If
you're interested in processing your HDR corona, I invite
you to follow the tutorial that Lorenzo Comolli prepared
after the USA 2017 eclipse. On 27 January 2018 Lorenzo was
invited by VVS association in Belgium for presenting at
the Astrofotografiedag 2018, a conference about
astrophotography. One of the presentations was on how to
process the great American eclipse. Look
also to the other presentation on the dedicated page. |
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