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Solar eclipses are magnificent natural phenomena during which the sun is obscured by the moon. Besides the unique opportunity of studying the solar corona and immediate vicinity of the sun, an eclipse also leads to a darkened daytime sky with sunset colors and many other fascinating phenomena. Here we focus on how the daytime horizontal visual range changed during the duration of the solar eclipse of 21 August 2017, observed from Rexburg, Idaho, USA. Close to totality the eastern horizon for a short time period showed the contours of the Grand Teton Mountains from distances between about 80 km to 90 km. We show and discuss photographic images that show the visual range during totality being significantly extended beyond the visual range in most of the partial phase before and after totality, which was below 80 km when the mountains could not be seen by the naked eye. This phenomenon of an extended visual range can be explained in terms of a simple model for the daytime visual range. This model, which will be explained in this presentation, nicely reproduces the observations and also predicts other phenomena; for example, it predicts that similar phenomena may be observed if part of the line of sight close to the observer is in deep shade of a thick cloud cover. The presentation will tie these observations and their explanation to the teaching of optical scattering and atmospheric optics. 

Mirages, rainbows, halos, glories, and coronas are well-known atmospheric optics phenomena that can be used as examples when teaching the well-understood underlying optical principles of refraction, reflection, dispersion, diffraction, and scattering. These beautiful natural phenomena can generate interest when used for teaching optics because they usually are easily observable with the naked eye. The invention of Si-sensor-based digital photography, however, also offers easy investigations in spectral regions adjacent to the visible range. We report and discuss observations of natural phenomena with a modified DSLR camera operating in the near infrared spectral range above 800 nm. This investigation may be particularly useful in photonics education, as the discussion of photon detectors in certain wavelength ranges can be combined with atmospheric optics, which always attracts interest in students. 

There are many interesting ways in which optics and meteorology intersect and provide cross-discipline learning opportunities. One example is the use of thermal imaging to illustrate the principles underlying urban heat islands (UHIs), found on scales from the mesoscale to the microscale, which give rise to increased temperatures in urban settings. The most common way of documenting such phenomena is through traditional meteorological measurements. This presentation describes the use of a thermal infrared imager to document and help explain micro-scale UHIs observed initially as a persistent difference in air temperature measured by two nearly identical weather stations separated by 2.79 km in Bozeman, Montana. Mobile meteorological measurements from a backpack-mounted weather station, carried throughout the surrounding area at different times of year and compared with the stationary campus weather station, verified the presence and scale of a micro-heat island. This also identified one such micro UHI that existed when the immediate surroundings contained man-made materials such as concrete and asphalt adjacent to natural vegetation. Thermal images from the radiometrically calibrated imager recorded the diurnal thermal signature of manmade and natural surfaces. The thermal images help to explain process that are occurring, whereas most traditional meteorological instrumentation may not provide process-based information. Time-series plots of the infrared brightness temperatures show that the man-made materials emit elevated levels of thermal radiation long after the end of direct solar heating, while natural vegetation quickly comes into thermal equilibrium with the ambient air. The combination of traditional and nontraditional instrumentation document and explain processes occurring in micro UHIs that vary rapidly in space with changing ground cover.