Direct Imaging and Gradient-Based Analysis of the 12 August 2026 Partial Solar Eclipse from a Freely Rotating High-Altitude Balloon

Abstract

We report a proof-of-concept observation of the partial solar eclipse of 12 August 2026 using a freely rotating high-altitude balloon launched from Oldenburg, northern Germany. The payload carried two Insta360 ONE RS cameras equipped with 4K Boost wide-angle lenses; covered by filter material taken from a BRESSER eclipse viewing glass. Interval photographs were acquired every 10 s at ISO 800 and 1/1000 s. Of approximately 1,300 images, 21 contained a directly visible image of the eclipsed Sun, spanning 19:19:15-20:38:21 CEST and both sides of the local eclipse maximum. To test whether quantitative eclipse information could be recovered from these small, non-stabilized wide-angle images, the visible solar area was estimated using a two-dimensional gradient-based solar edge analysis and normalized to the first observation. The image-derived obscuration followed the independently calculated eclipse geometry with Pearson r = 0.959, a mean absolute difference of 9.5 percentage points, and an RMSE of 11.5 percentage points. Systematic deviations are consistent with the limitations of an uncalibrated action-camera system, including point-spread function, field-dependent lens response, filter geometry, and camera-to-camera differences. The results demonstrate that passive payload rotation can yield both visually useful and semi-quantitative direct eclipse observations without active solar pointing, and define a calibration strategy for future balloon-borne eclipse measurements.