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The 2017 Great American Eclipse 1.3

Updated: Mar 20

17.08.21 - Composite Images: It is difficult to see a total solar eclipse based on the logistics of travel and photography alone, but it is equally difficult to capture the full range of phenomena surrounding the event in the limited time provided. A considerable amount of the detail and mechanics at play are obfuscated by the incredible contrast between light and shadow, and the passing of time itself. However, one of the great strengths of digital photography is the ability to compile multiple photos into a single composite image that provides insights into the veiled reality that exists beyond the capabilities of both our eyes and the camera alone.


High contrast image of totality detailing the solar corona
9 bracketed images stacked into a final, high-contrast composite


It is easier than ever to predict the approximate path of the sun using augmented reality (AR) tools such as PhotoPills and Sky Safari. However, predicting the actual path precisely is still challenging because the AR functions are locked into the aspect ratio, focal length, and orientation of my phone instead of the larger cameras that I use for imaging. This is especially complicated for long-exposure and timelapse photography which don't allow for downstream modifications to correct for location and/or orientational inaccuracies. In the end, it's still just a hopeful, educated guess.


I located my D750 on a tripod low along the ground on the edge of the lake so I could get both the lake and the Sun's high orbital path in the frame. Even with the very wide 14mm lens, it was difficult to get both objects in frame at the same time. I set up the Nikon D750 to take photos every 6 seconds for the duration of the eclipse (around 1,760 images total over about 3 hours). At the cinematic standard of 24 frames per second (fps), that resulted in an approximately 73 second timelapse video.


However, this type of event does not lend itself to standard timelapse methods. The light intensity of the environment drops dramatically during a total solar eclipse and the parameters that the camera generally uses to estimate correct exposure are not compatible with the dark, low contrast conditions of totality. For this reason, I had to modify the exposure manually over the duration of the event.


Exposure Value - In photography, light intensity can be simplified into a single numeric approximation known as Exposure Value (EV). Exposure Value is calculated based on the aperture and shutter speed settings (ISO has a tertiary role). Each integer increase in EV (ie. moving from 1EV to 2EV) indicates a doubling in brightness, and each step reduced is roughly half (50%) as bright. During the 2017 eclipse the daytime images were about 18EV (1/3200, f8, ISO 200), while during totality it was about 8EV (1/20, f3.5, ISO 200) which is a 10EV reduction in brightness or approximately 1000% dimmer. To put that into units of luminance, full, unobstructed daylight generally has an intensity of about 10,000 foot candles (Fc), but during totality the luminosity was around 10 Fc which is barely enough light to read by.

While manually adjusting the exposure provided groups of well exposed frames, when combing them into a video, it initially left me with jagged transitions at each modification of shutter speed or aperture. It would have taken months to manually smooth the transition between each exposure, but fortunately I found the fantastic application LRTimelapse to help me balance the gradual transition between exposures and combine the 1,760 images into the following 41 second timelapse video of the event (also available in 4k on my YouTube channel):


Wide Angle Timelapse (4k video)

If you watch the video carefully during totality, you can see the elliptical shadow of the Moon move across the sky from right to left during the few frames of that brief 2 minutes starting at about 19 seconds. I slowed down the frame rate considerably during totality so that more detail can be seen in that brief period of time. For the 2024 eclipse, I plan to take more images during totality to provide more detail of the sky's transition during the event.


Even though the timelapse was able to capture the slow transition of the sky over the duration of the event, it didn't provide any insight into how the pictures of the partial phase corresponded with the Sun's movement across the sky. To provide this information, I took a single image at max totality and superimposed the 20 images of the partial eclipse on both sides in Photoshop to create a composite image that depicts the approximate position of the Sun and Moon during each phase of the eclipse.


Partial phase overlay of wide angle total solar eclipse image
Twenty partial phase images flanking the fleeting moments of totality

As is usually the case, the actual orbital mechanics at play were not readily understandable just by viewing the eclipse from the ground. As mentioned previously, while the Sun appears to move across the sky from East to West, it is actually our position on the Earth rotating away from the Sun that makes it appear to move across what we loosely refer to as "the sky." The long, arcing path of the solar eclipse is caused by the Moon moving between the Sun and the Earth (across the Ecliptic) casting a shadow that moves across the Earth's surface. The actual path of the shadow (especially how it is perceived from the surface of the Earth) is also affected by the Earth's rotation away from the event, and the curvature of the Earth (which is why the ellipse elongates at the beginning and end of the path), but that is much more complicated discussion.


However, while aligning the partial phase images, I began to see a pattern in the Moon's movement across the Sun which accurately depicted the differences between the orbit of the Moon, and the Earth's orbit around the Sun which I have labeled in the graphic below.


2017 Total Solar Eclipse Transit Diagram
Click on the image to enlarge if text is too small to read.

The path of sunlight from the sun to the Earth is essentially constant along what is known as the Ecliptic. The Moon passes over the ecliptic twice every time it completes an orbit around the Earth (every 27.3 days). On rare occasions, the Moon happens to cross the plane of the ecliptic at the same time as the Sun is moving across the same point. When the alignment is not quite perfect, we have a partial eclipse. When the Moon is closer to apogee (the farthest point in its orbit from Earth), the relative size of the Moon is smaller than the Sun which leads to an annular eclipse (ring of fire). On this day however, the Moon was closer to perigee (the closest point in its orbit from the Earth), so the relative size of the Moon was slightly larger than the Sun, leading to a total solar eclipse.


The graphic above describes the interaction between the Sun and Moon, but we don't perceive it in this way from the curved, rotating surface of the Earth. To help translate the relationship to our Earthly perspective, I superimposed the orbits onto the partial phase composite. In the diagram below, we are viewing the Sun looking slightly to the Southeast, so the Earth (and thus my viewing position) is rotating to the left (East) of the frame making the Sun appear to move to the right (West).


It is important to note that while the ecliptic in this graphic is consistent throughout the duration of the eclipse, the Moon's orbit shifts to the West with the Sun because the Earth's rotation around its axis occurs faster than the Moon moves in its orbit. So a more accurate graphic would have lines indicating the Moon's orbit at every partial phase, but that would make for a very cluttered image.


Augmented reality overlay of transit diagram
The eclipse transit diagram superimposed with our view of the event

The difference in illumination (dynamic range) of the darkened sky, the secondary reflection of the light from the Earth off the Moon (Earth glow), and the brilliance of the corona around the Sun is vastly greater than the capabilities of any modern camera. However, photographic software has advanced so much since I started photographing that it is now possible to compile multiple images of increasing exposure levels in order to pull out the incredible detail hidden beyond the capability of our eyes. I used 9 exposures ranging form -4 to +4 EV and combined them to create a composite HDR image that gives a more expansive view of the conjunction of the Moon, the Sun’s Corona, and the stars that poked through the veil.


I originally created this HDR image in 2017 using Aurora HDR, but this software is no longer available as a standalone application, and is instead now a part of Luminar Neo.


Natural Totality Solar Corona image.

However, the more natural lighting and tones of the original image obfuscated some of the fine detail in the corona and the sky, so I pushed the data further to accentuate the nuanced patterns and the surrounding stars. This created a few unwanted artifacts, but the increased contrast was perfect for labeling the eclipse's components and the surrounding stars of Constellation Leo.


2017 Total Solar Eclipse Totality Diagram
Click on the image to enlarge if text is too small to read.

In previous posts I shared diagrams that included the 20 partial eclipse phase images flanking a single image of totality. However, a diagram doesn't give a good sense of movement, so I decided to create a brief timelapse video using only the primary frames of the event (23 in total). It took a very long time to align all the frames, compensate for all the rotation of the sun in the frame of my camera (explained in more detail below), and create the video, but it helps make the information more dynamic.


Telephoto Timelapse (4k Video)

I didn't have a star-tracking mount at the time of this eclipse, so I have had to overcome a number of alignment issues with my images as the movement of my camera was locked into the azimuthal movement of a geared head (which moves vertically, horizontally, and rotationally) instead of the equatorial movement of the Earth around its axis. The following image shows the roughly 67 degrees of clockwise rotation that manifested in my images from the beginning to the end of the eclipse.


Sun rotation diagram
The Sun slowly rotated approximately 67 degrees clockwise in-frame during the eclipse

To compensate for the rotation, I overlayed the 23 images in Photoshop and carefully aligned them one by one. I used different methods of comparing the layers to help with alignment, but the only real reference points were the sun spots and the silhouette of the Moon. While playing around with overlaying methods, I found the emerging pattern of the overlaid partial phases to be very interesting, similar to opposing sound waves passing through each other. The variation in the width of a few of the arcs is due to the fact that I could not take images at exactly 9 minutes apart because of persistent conflicts with passing clouds (as you can see in the timelapse video).



Even if I had the camera set up on a perfectly tracking equatorial mount, it is important to note that the Sun is not stagnant either. The Sun rotates on its axis approximately every 27 days, but compared to the relatively stagnant surface of the Earth, the "fluid" dynamics of the Sun's amorphous surface engender notable differences in its rotation from slower rotation at the poles to faster rotation at the equator. Since my camera cannot render the churning surface of the Sun (that requires very expensive telescopes and very narrow H-Alpha filters), the movement of the surface was only evident in the path of the Sun Spots visible on that day. Over the roughly 3 hours of the eclipse, a combination of the Sun's rotation and the migration of the spots across the Sun's surface lead to a notable change in position that was only evident once I had manually aligned the images.


Solar surface movement gif
Animated GIF of how the Sun spots moved from left to right during the eclipse (updated 2.9.24)

We returned from the eclipse to the ravages of hurricane Harvey, followed by the creation of this website, the birth of our first child, moving to a new home, and much more. In that process, all the images and composites I hoped to make from the data I captured on the day of the eclipse had to wait. However, with the excitement of the eclipses in 2023 and 2024, I finally made the time to work on all these images over the span of many months. It took a a lot of work to create all these composites, but in the end I think they were worth the effort and tell a story the single images could not. Additionally, what I learned while creating them has provided important insight into what I want to do in 2024 when the total solar eclipse comes to Texas.


C2 phase diamond ring
C2 phase that I missed with my telephoto rig which was captured by the D750 at 14mm

This concludes my images and videos for the 2017 Total Solar Eclipse. I look forward to taking what I have learned from my first eclipse and putting that knowledge towards the next one. I hope to see you all in Central Texas April 8, 2024 for one of the greatest shows on Earth



See how the trip started: The 2017 Great American Eclipse 1.1

See detailed images from each phase: The 2017 Great American Eclipse 1.2

Detailed Eclipse Photography Guide: How to Photograph a Solar Eclipse




© 2017-2023 Shaun C Tarpley

 
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