Time-resolved photographic dataset of the total lunar eclipse (27–28 July 2018) acquired with a Nikon D7500

Time-Resolved Photographic Analysis of the Total Lunar Eclipse (27–28 July 2018) This document summarizes the scientific interpretation and analysis of a georeferenced, time-resolvedphotographic dataset documenting the total lunar eclipse of 27–28 July 2018. The dataset consists of 128high-resolution digital photographs acquired with a Nikon D7500 camera and archived on Zenodo as a compressedZIP file. The images were recorded from a fixed terrestrial location in Wangen (ZH), Switzerland, at geographiccoordinates 47.409283° N, 8.643662° E, approximately 430 m above sea level. The availability of precisegeographical coordinates together with original EXIF timestamps allows the full observation geometry to bereconstructed for each image. 1. Nature of the Dataset The dataset constitutes a passive observational experiment of a natural radiative transfer system. The Sunacts as the primary light source, the Moon as a diffusely reflecting test object, and the Earth’s atmosphereas a wavelength-dependent transmission filter. The Earth’s shadow (umbra and penumbra) serves as a dynamicaperture controlling the incident radiation. All images were acquired with identical instrumentation, optics, and sensor configuration, and containoriginal EXIF metadata including acquisition timestamps. This ensures chronological consistency and allowsthe dataset to be treated as a true georeferenced time series. 2. Temporal Structure The dataset spans three main physical phases: Phase A – Reference (26 July 2018):Images recorded one day before the eclipse provide a baseline reference of the Moon under direct solarillumination. These frames represent standard atmospheric transmission conditions and serve as a controlstate for comparison. Phase B – Total Lunar Eclipse (27 July 2018):The Moon becomes fully immersed in the Earth's umbra. Direct sunlight is completely blocked and the lunarsurface is illuminated exclusively by sunlight refracted and scattered through the Earth's atmosphere.Short wavelengths are preferentially scattered (Rayleigh scattering), while longer wavelengths (red andorange) dominate the transmitted spectrum. This produces the characteristic "Blood Moon" appearance. Phase C – Recovery and Ghost Moon (28 July 2018):The Moon gradually exits the umbra and penumbra. At low elevation angles, the Moon remains strongly attenuatedby atmospheric extinction, producing low contrast and pale coloration. These frames capture the limit ofvisual detectability under high air mass conditions. 3. Geometrical and Physical Interpretation With known latitude, longitude, altitude, and acquisition times, the full Earth–Moon–Sun geometry can bereconstructed for each image. This enables calculation of lunar altitude, azimuth, and air mass for everytime step. The dataset therefore represents a georeferenced observational record of atmospheric transmission. TheEarth’s atmosphere behaves as a large-scale optical filter, with the eclipse geometry producing anintegrated transmission measurement along the Earth's limb. This process can be described by the Beer–Lambert law: I = I0 · exp(-k · m) where I is the observed intensity, I0 the original solar intensity, k the atmospheric extinction coefficient,and m the optical air mass. During totality, the effective air mass becomes extremely large, leading to strongspectral filtering and reddening. 4. Statistical and Methodological Validity Because all instrumental parameters remain constant throughout the series, the only variable in the systemis the geometric configuration of the Earth–Moon–Sun system. This makes the dataset conceptually equivalentto a controlled radiometric experiment. The presence of accurate geodata transforms the dataset from a qualitative photographic sequence into aquantitatively interpretable physical observation. The data can therefore be used for semi-quantitativeanalysis of brightness, color channels, contrast, and atmospheric extinction as a function of time andviewing geometry. 5. Scientific and Educational Relevance This dataset is suitable for:- Teaching atmospheric optics and radiative transfer- Demonstrating Earth shadow geometry and eclipse mechanics- Outreach and public science communication- Image processing and photometric exercises- Comparison with astronomical ephemerides and atmospheric models The dataset provides a visually intuitive demonstration of how planetary atmospheres modify radiation,using the Moon as a natural calibration target. 6. Conceptual Significance From a scientific perspective, the dataset represents a natural experiment in which planetary-scale opticalphenomena become directly observable. The Earth itself functions as an optical instrument, and the Moon actsas a projection screen for atmospheric physics. In this sense, the dataset captures not only a rare astronomical event, but also a direct measurement of theoptical properties of the Earth's atmosphere integrated over global spatial scales, embedded in realspace-time through precise georeferencing.