High Resolution 2017 Total Solar Eclipse

Totality: High resolution eclipse

I observed the eclipse from Unity, Oregon. Oregon was the chosen beforehand because it provided the best prospects in terms of cloud cover, and also because of the time of the eclipse in the morning which is often the best moment to get the best seeing conditions.

The area of Unity was chosen on August 19th as the forecast looked optimal in terms of sky transparency, with totally clear sky during the eclipse, both free of any cloud and free of dust/smoke from the summer wildfires. I scouted the area of Unity observing the sun with a spotting scope on the morning of 20th to find the best location for seeing. The overall seeing was very good everywhere with still notable differences in local turbulence.

Apparently it payed off, because the seeing was really excellent, with good images during the whole eclipse, and more important, perfect seeing during the crucial stage of totality. The conditions were really optimal, with the last cirrus clouds receding to the east at sunrise, and not a trace of smoke or dust in the sky.

I used a 100mm apochromatic refractor with a 42Mpix DSLR to image the eclipse.

totality_reducedComposite 2017 Eclipse (high res here): the image is a high resolution composite of more than 70 images acquired with different exposure time. With its high resolution (< 2 arcsec details) over a large 2°x1.5° field of view, this image might be the most detailed image of a solar eclipse ever produced. 

totality_closeupHigher resolution, close up view of the inner corona (high res here). The inner corona is very rich in small scale details and reveals intricate magnetic structures.

high contrast corona_okHigh contrast view of the solar corona (high res here)

full_scale_prominencesFull resolution details of the solar prominences and their associated magnetic loops (full res here)

Those high resolution images are very close to diffraction limit over the whole FOV. More than 80 images with exposure time ranging from 1/250s to 5s were acquired during the 129 seconds of totality. On the composite, stars down to magnitude 13 are visible. Needless to say that the the results are above my wildest expectations for my first time seeing the solar corona.

With its high resolution (< 2 arcsec details) over a large 2°x1.5° field of view, this image might be the most detailed image of a solar eclipse ever produced.

The processing is inspired by the pioneering work of Pr. Druckmuller. I had to write my own code for all the critical steps of processing: sub-pixel image registration on the coronal feature, optimal composition of images to get a seamless HDR composite, and enhancement of the coronal details using adaptive filters. This work represents many hundreds of hours. I  thank eclipse chasers Christian Viladrich, Larry Stevens and Jean-Marc Lecleire for sharing some of their eclipse images so that I could work on the image processing before the eclipse happened.

Scope Skywatcher Black Diamond, 100mm diameter S-FPL53 apochromatic doublet, 900mm focal length.

Scope baffling was optimized to improve contrast.

Corrector Homemade field flattener Design correcting both field curvature and astigmatism.

4-layer-AR-coating on lenses for best contrast.

Imager Sony A7RII 42Mpix camera, 4.5µm size pixels for diffraction limited sampling. Rental camera.

Earthshine

The Earthshine was particularly clear on the images with longest exposure. Using the images with longest exposure (5s, 2.5s, and 1.3s), I created a dedicated image of the Earthshine. Very small details on the moon are visible, like Rima Hyginus, walls of Copernicus crater, Vallis Alpes, etc…

Those features are generally hard to catch on usual Earthshine images with small crescent; here, the 45° elevation of the eclipse and good seeing allowed for very detailed view of the lunar surface. The pinkish color spots of color on the right hand side of the lunar limb are due to the the bright prominences that scattered around some of their colored light.

The total exposure time used for this image is around 70 seconds, which allowed to obtain very good signal to noise ratio and to reveal all the lunar surface details.

earthshine_okThe Earthshine (high res here) shows the well-known lunar details. It comes from solar light scattered by Earth clouds, ocean and land, dimly litting the Moon surface. 

C2 and C3

The location chosen was about 5km (3miles) South of the center line of the eclipse path in order to get nice Baily’s beads at C3.  This location even provided 1s longer eclipse duration compared to center line because of the irregular lunar profile.

But it all happened too fast and I did not see any Baily’s beads as I was looking at the 360° sunset during C3. Fortunately, the camera did its job and recorded them.

contacts_reducedComposite of C2 and C3 (high res here). C2 was a solitary diamond ring, while C3 featured beautiful Baily’s beads.

contacts_jubierCalculated contacts using Xavier Jubier’s excellent Google maps tool. The predicted contact appearance matches perfectly the recorded contacts.

Coronal motion and coronal features

During the totality, the camera was driven in order to take successive sets of 9 exposures bracketed images. Exposure durations were 1/50s, 1/25s, 1/12s, 1/6s, 0.3s, 0.6s, 1.3s, 2.5s and 5s. Altogether, 8 successive 9-exposures-sets, ie 72 images, were acquired during the totality. Shorter exposures where used around C2 and C3 to get prominences and contacts.

Each successive 9-exposures-set of images was processed independently to get 8 successive HDR composites of the solar corona. After removing the lowest spatial frequencies of these 8 HDR composites, the 8 successive HDR composites were animated.

The most obvious is the motion of the moon disk in front the solar corona during the totality. More interesting, the animation reveals many dynamic features in the solar corona moving quickly enough to be seen during the short duration of totality from a single location.

The outflow of a CME on the left hand side quadrant of the sun is particularly well visible with surprisingly large displacements. Many other features with smaller scale displacements are visible, like in the polar plumes.

The displacement of the solar corona in front of the background stars (due to Earth annual revolution around the sun) is also visible. It amounts ~4 arcseconds.

anim_OK+closeups_gif_generationOpen link in another window to see the animation in full resolution. Notice the complex outflow of the CME (purple close up), a very active polar plume at the bottom (green close up), as well as the debris of a dissipating prominence (right edge of the blue close up) that shows its pink color on the color composite

Left (high res here): SDO spacecraft animation (AIA304) showing the dissipating prominence at the time of the eclipse. The last debris of the prominence are visible on the high resolution image I obtained and the animation below . Right (high res here): SOHO spacecraft animation (LASCO C2) showing the CME on the left quadrant during the eclipse that is easily visible on the high resolution image and animation. Another weaker CME on the upper right quadrant is visible before the eclipse. It shows up as some irregular structure alike a turbulent flow on the color composite.

Partial phases

The partial phases provided a progressive rise of the tension as as the moon glides over the sun surface. On top of this, another source of excitement was the seeing. As the sun rose, the images were becoming more and more steady. Around 20 minutes before C2, I knew the seeing was going to be perfect: it was already the best conditions I ever had during my practice solar images, and it kept improving.

Indeed, the conditions were perfect during totality, with zero blur due to atmospheric turbulence, and even rarer, almost non existent local distortion in the images, which provided sharp images over the full field of view.

After Totality, the fast rise of temperature quickly degraded the image quality.

Some images of the partial phase (high res 1, 2, 3, 4). Opening the images in full resolution, it is possible to see how the seeing improved before Totality, and degraded after Totality.

sunspots_okAnimation (full resolution here) showing some changes of the sunspots group before and after totality. Sunspots appear brown compared to the pitch black lunar disk. Although the sun elevation was ~37° and ~50° when the images were acquired, the ~1 arcsecond atmospheric dispersion is readily visible as a respectively blue/red fringe on the edge of the lunar disk.

 

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