@article{Vollmer2025, author = {Vollmer, Michael}, title = {Nachtsicht ins All mit dem bloßen Auge: Sag mir, wie weit die Sterne steh'n}, series = {Physik in unserer Zeit}, volume = {2025}, journal = {Physik in unserer Zeit}, publisher = {Wiley}, doi = {10.1002/piuz.202501751}, pages = {2 -- 10}, year = {2025}, language = {de} } @article{Vollmer2025, author = {Vollmer, Michael}, title = {Naked eye celestial objects and phenomena: how far can we see at night?}, series = {European Journal of Physics}, volume = {46}, journal = {European Journal of Physics}, number = {3}, publisher = {IOP Science}, doi = {10.1088/1361-6404/adbf74}, pages = {18}, year = {2025}, abstract = {How far can we see with the naked eye at night? Many celestial objects like stars and galaxies as well as transient phenomena such as comets and supernovae can be observed in the night sky. We discuss the furthest distances of such objects and phenomena observable with the naked eye during the night-time for Earth-bound observers. The physics of night-time visual ranges differs from that of daytime observations because human vision shifts from cones to rods. In addition, mostly point sources are observed due to the large distances involved. Whether celestial objects and phenomena can be detected depends on the contrast of their radiation and the background sky luminance. We present a concise overview of how far we can see at night by first discussing the effects of the Earth's atmosphere. This includes attenuation of transmitted radiation as well as its role as a source of background radiation. Disregarding the attenuation of light due to interstellar and intergalactic dust, simple maximum night-time visual range estimates are based on the inverse square law, which can be easily verified by laboratory and demonstration experiments. From the respective calculations, we find that individual stars within the Milky Way galaxy of up to 15 000 light years are observable. Even further away are observable galaxies with several billion stars. The Andromeda galaxy can be observed with the naked eye at a distance of around 2.5 million light years. Similarly, the observability of supernovae also allows a visual range beyond the Milky Way galaxy. Finally, gamma ray bursts as the most energetic events in the universe are discussed concerning naked eye observations.}, language = {en} } @article{Vollmer2025, author = {Vollmer, Michael}, title = {How far can we see at day?}, series = {European Journal of Physics}, volume = {46}, journal = {European Journal of Physics}, number = {3}, publisher = {IOP Science}, doi = {10.1088/1361-6404/adc4a0}, pages = {17}, year = {2025}, abstract = {We discuss the farthest objects on Earth observable for the unaided, healthy naked eye during the daytime, i.e., the maximum visual range for observers on Earth. Visual range depends first on the properties of the material between observer and object and its interaction processes with radiation, but second also on our visual perception system. After a rough comparison of ranges in water, glass, and the atmosphere, we focus on the physical basis of visual range for the latter. As a contrast phenomenon, visual range refers to allowed light paths within the atmosphere. It results from the interplay of geometry, refraction, and light scattering. We present a concise overview of this field by qualitative descriptions and quantitative estimates as well as classroom demonstration experiments. The starting point is the common geometrical visual ranges, followed by extensions due to refraction and limitations due to contrast, which depend on scattering and absorption processes within the atmosphere. The quantitative discussion of scattering is very helpful to easily understand the huge ranges in nature from meters in dense fog to hundreds of kilometers in clear atmospheres. Extreme visual ranges from about 300 km to above 500 km require optimal atmospheric conditions, cleverly chosen locations and times, and a sophisticated topography analysis. Even longer visual ranges are possible when looking through the vertical atmosphere. From the ISS, daytime ranges well above 1000 km are possible.}, language = {en} } @incollection{Vollmer2025, author = {Vollmer, Michael}, title = {Elektromagnetische Wellen - Grundlagen und ausgew{\"a}hlte Anwendungen}, series = {Schwingungen und Wellen in Alltagskontexten}, booktitle = {Schwingungen und Wellen in Alltagskontexten}, edition = {1}, publisher = {Springer}, doi = {10.1007/978-3-662-70949-8_3}, pages = {35 -- 48}, year = {2025}, abstract = {Schwingungen und Wellen zeigen sich in vielen Alltagsph{\"a}nomenen der Physik, d. h. in der Lebenswelt von Sch{\"u}lerinnen und Sch{\"u}lern. Dazu z{\"a}hlen in der Mechanik Beispiele wie Schaukeln, Seilwellen oder Wasserwellen am Strand, in der Akustik Schallwellen durch beliebige Ger{\"a}usche oder stehende Wellen in Musikinstrumenten und im Elektromagnetismus die allgegenw{\"a}rtigen elektromagnetischen Wellen. Letztere haben vielf{\"a}ltigste Anwendungen, z. B. Erhitzen mit Mikrowellenger{\"a}ten, Kommunizieren mit Smartphones, Daten{\"u}bertragung mit Lichtleitern oder Fotografieren mit Kameras, ganz zu schweigen von medizinischen Anwendungen der Endoskopie, des R{\"o}ntgens oder laserbasierten chirurgischen Eingriffen. Viele dieser Anwendungen haben ein enormes Motivationspotenzial in der Lehre, weshalb das Thema fest in Lehrpl{\"a}nen der Sekundarstufen verankert ist. Im Folgenden werden zun{\"a}chst allgemeine Grundlagen und Gemeinsamkeiten der Beschreibung beliebiger Wellen diskutiert, bevor das Hauptaugenmerk auf elektromagnetische Wellen und ausgew{\"a}hlte Anwendungen gelegt wird.}, language = {de} } @article{Vollmer2024, author = {Vollmer, Michael}, title = {Optical Phenomena in the Atmosphere}, series = {Encyclopedia of Atmospheric Sciences}, journal = {Encyclopedia of Atmospheric Sciences}, number = {2}, edition = {3}, publisher = {academic press}, doi = {10.1016/B978-0-323-96026-7.00177-6}, pages = {285 -- 306}, year = {2024}, abstract = {Following a brief description of the atmosphere and spectra of the Sun as dominant daytime light source, the most common optical phenomena within the troposphere are discussed, which are due to scattering of radiation with the constituents of the atmosphere. At first mirages, rainbows, coronas, iridescence, glories and halos are explained. Then light scattering phenomena which give rise to sunset colors, blue and colorful skies are presented as well as related phenomena like blue mountains, white clouds, green flashes and visual ranges. The review ends with a short survey of other less easily observable optical phenomena of the atmosphere and a very detailed bibliography.}, language = {en} }