caa a22 4500 606166483 CHVBK 20210128100658.0 cr unu---uuuuu 210128e20150601xx s 000 0 eng 10.1007/s10440-014-9989-6 doi (NATIONALLICENCE)springer-10.1007/s10440-014-9989-6 Broer Henk Groningen, The Netherlands aut Near-Horizon Celestial Phenomena, a Study in Geometric Optics [Elektronische Daten] [Henk Broer] Near horizon phenomena, like blank strips in the setting sun or Fata Morganas, can be largely understood in terms of geometric optics. Here the existence of a warm layer above the observer in which light rays can be either refracted of reflected, already suffices to explain many of the phenomena; a reasoning which goes back to Alfred Wegener in the 1920's. We review this theory, where first the atmosphere is divided into discrete, optically homogeneous layers, and where later the atmosphere is considered as a continuous, isotropic medium. Thus the theory gets embedded in differential geometry, where light rays are geodesics. Asimplifying assumption is that the refraction index only depends on the elevation above the surface of the earth. Here a connection is made with the geodesic problem on a surface of revolution. In the background of this we touch the variational calculus as this runs from Bernoulli to Hamilton, all the way maintaining a completely anachronistic viewpoint. Springer Science+Business Media Dordrecht, 2015 Geometric optics nationallicence Differential geometry nationallicence Nonlinear dynamics nationallicence Acta Applicandae Mathematicae Springer Netherlands 137/1(2015-06-01), 17-39 0167-8019 137:1<17 2015 137 10440 https://doi.org/10.1007/s10440-014-9989-6 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s10440-014-9989-6 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Broer Henk Groningen, The Netherlands aut NATIONALLICENCE 773 0- Acta Applicandae Mathematicae Springer Netherlands 137/1(2015-06-01), 17-39 0167-8019 137:1<17 2015 137 10440