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Eclipse 2024

The 2017 total solar eclipse provided the first successful measurement of gravitational deflection due to the Sun’s mass, since 1973. That eclipse was only 2 minutes long, but provided the most accurate deflections ever recorded by a telescope on Earth. In 2024, an even better opportunity arose, and I helped others make the most of it. It was cloudy in Leakey, TX, as seen in this video, so instead of seeing the corona and lots of stars, the clouds acted as a filter and I imaged some prominences during some small breaks. Fortunately, members of the MEE2024 group in El Salto, MX, had fairly clear skies. They are processing their images and expect to get good results.

The Springs Retreat in Leakey was the ideal place to set up my telescope, along with 10 others from Oregon, Texas, and London. My setup shown here used a Tele Vue NP101 with a Baader CMOS red filter and a ZWO2600MM Pro camera. On the same plate was a Tele Vue TV-85 telescope, Tele Vue 0.8x reducer/flattener, ATIK red filter, and a ZWO1600MM Pro camera. Not seen, but between these telescopes was a 135mm focal length Askar lens with a ZWO183MM camera. That camera was supposed to look for Vulcan or other intra-Venus asteroids. Based on some tests, I could have detected objects on the order of 100m diameter. To run these telescopes, I needed two laptops, each with their own sun shade.

The NP101 telescope took images using 250msec exposures at zero gain, recording at 3.5 images per second. The TV-85 used 50msec exposures at zero gain, and was able to record 11.5 frames per second. This shorter exposure was picked to allow getting stars as close as possible to the Sun’s limb, without the corona saturating the camera. Others in the MEE2024 group used longer exposures, with the goal of getting dimmer stars further from the Sun.

The NP101 was re-focused during totality by observing some sunspots. I had only a few seconds, and it turns out the final focus was not very good. I estimate the blur was 4 to 5 arcseconds. The TV-85 focus seemed more stable when practicing focus on stars during twilight compared to night-time, so I did not attempt to refocus the telescope. The prominences from that telescope looked pretty good, so that is what I show in this summary.

The Bisque Paramount MyT was the same one I used in 2017, and could just support the total weight. I used a Celestron tripod that was augmented with braces on the lower part of the legs, with a 25lb weight to add tension. Under each foot was a 3” diameter steel disk with a 1” button, which helped stabilize the tripod on the hard sandy/grassy ground.

The four nights before the April 8 eclipse were clear, so I took about 10 zenith calibration images (each 3sec, 20 raw images) each night, with both Tele Vue telescopes. The distortion coefficients would have been used in the eclipse images to get accurate deflection results.

The imaging during totality was totally automated, so I could enjoy the eclipse naked-eye. The first 50 seconds of totality were used to take images about 10 degrees right of the Sun, then 160 seconds pointed at the Sun, then 50 seconds pointed about 10 degrees to the left of the Sun. Those side images were to get plate scale calibration data. The clouds prevented recording any stars in those series. I did process the 160 seconds of mid-totality data by going frame-by-frame and measuring the brightness of the strongest prominence. The result is shown in the graph. If the signal was greater than 66000 counts, that frame was saturated and was not used for analysis. It is obvious that there was a few seconds of clouds thin enough to see through near the start and toward the end of the 160 period. The clouds were moving quickly enough so that I averaged some frames to help reduce the wide intensity variations across the disc. I used frames 49-60, centered at 13:31:29 to get a good image of the prominence on the right side of the Sun. Those frames averaged about 42000 counts, so none were saturated. I did the same kind of averaging for frames 152-177, centered at 13:31:42, and frames 1030-1040, centered at 13:33:28. Note that C2 occurred at 13:30:32.

These best averages are shown in the next figures. The one on the left is the series at 13:33:28. The center image is for reference (13:31:42) and the image on the right is the one at 13:31:29. Other eclipse observers who started earlier saw a brighter portion of that long prominence, a little closer to the Sun.

After several years of preparation and practice, I was ready to get thousands of stars at perfect focus, allowing a very good determination of not only the relativistic gravitational deflection coefficient (1.75 arcsec/R), but also show that the 1/R relationship is precise. Unfortunately, all I was able to do was get some pretty pictures of prominences. Transporting this equipment to Africa or Australia for the next good totalities in 2027 and 2028 is not likely.

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Web page last updated April 17, 2024.