TY - JOUR A1 - Vollmer, Michael T1 - Below the horizon-the physics of extreme visual ranges JF - Applied Optics Y1 - 2020 U6 - https://doi.org/10.1364/AO.390654 VL - 59 IS - 21 SP - F11 EP - F19 PB - Optica Publishing Group ER - TY - JOUR A1 - Vollmer, Michael A1 - Möllmann, Klaus-Peter T1 - Unsichtbares sichtbar gemacht: Infrarotkameras für Smartphones JF - Physik in unserer Zeit KW - Infrarotkamera KW - Smartphone KW - Temperaturmessung KW - räumliche Auflösung KW - qualitative Analyse KW - quantitative Analyse Y1 - 2020 U6 - https://doi.org/https://doi.org/10.1002/piuz.201901551 VL - 51 IS - 1 SP - 29 EP - 35 PB - Wiley-VCH ER - TY - JOUR A1 - Vollmer, Michael A1 - Möllmann, Klaus-Peter T1 - Wenn Licht die Biege macht JF - Physik in unserer Zeit Y1 - 2020 U6 - https://doi.org/https://doi.org/10.1002/piuz.202001569 VL - 51 IS - 1 SP - 46 EP - 47 PB - Wiley-VCH ER - TY - JOUR A1 - Vollmer, Michael T1 - Gefrierende Gewässer JF - Physik in unserer Zeit KW - Gefrieren von Seen KW - Eiswachstumsmodell KW - Konvektion KW - Strahlung KW - Stefan-Boltzmann-Gesetz KW - Wärmeleitfähigkeit KW - optische Eisdickenmessung Y1 - 2021 U6 - https://doi.org/10.1002/piuz.202001589 VL - 52 IS - 1 SP - 19 EP - 25 PB - Wiley-Blackwell ER - TY - JOUR A1 - Vollmer, Michael A1 - Eberhardt, Wolfgang T1 - Ein einfaches Modell für die Vorhersage von CO2 Konzentrationen in der Atmosphäre in Abhängigkeit von globalen CO2 Emissionen JF - PhyDid B, Didaktik der Physik, Beiträge zur DPG-Frühjahrstagung N2 - Es wird das vielleicht einfachst mögliche Modell vorgestellt, mit dem zeitabhängige CO2 Konzent-rationen c(t) in der Atmosphäre ausgehend von verschiedenen globalen Emissionsszenarien für CO2berechnet werden. Dazu wird eine einzelne inhomogene lineare Differenzialgleichung 1. Ordnung hergeleitet, deren Parameter sich aus den quantitativen Daten des global carbon project sowie Mauna Loa Daten für CO2 Konzentrationen errechnen. Das Modell wird erstens getestet am Zeitraum 1960 bis 2020 mit vergleichsweise guter quantitativer Übereinstimmung zu Messdaten. Zweitens wird für zwei typische IPCC Emissions-Szenarien ein Vergleich der Modellvorhersagen mit denen der kom-plexen IPCC Earth-System-Klimamodelle diskutiert mit qualitativer Übereinstimmung des zeitli-chen Verlaufs. Drittens werden Ergebnisse einiger ausgewählter neuer Emissionsszenarien präsen-tiert. Ungeachtet einiger Abweichungen zu komplexeren Klimamodellen zeichnet sich unser Mo-dell durch zwei wichtige Vorteile für die Lehre aus. Zum einen ist es sehr einfach für Studierende und begabte Schüler nutzbar, da die erforderliche Lösung der Differentialgleichung bereits mit han-delsüblicher Tabellenkalkulationssoftware wie z.B. Excel programmiert werden kann. Dadurch ge-stattet es zum anderen auch sehr einfach, den zeitlichen Verlauf von Emissionsszenarien zu verän-dern und innerhalb weniger Sekunden Veränderungen aufgrund geänderter Eingaben zu berechnen. Insofern eignet sich das Modell sehr gut als Einstieg in das Thema Klimamodellierung in einführen-den Hochschulvorlesungen zum Themenbereich Kohlenstoffkreislauf und Klimawandel. In der Schule kann es gegen Ende der Sekundarstufe 2 beispielsweise im Projektunterricht zum Themen-komplex Nachhaltigkeit in Physik und/oder Mathematik eingesetzt werden Y1 - 2024 UR - https://ojs.dpg-physik.de/index.php/phydid-b/article/view/1411 SN - 2191-379X VL - 1 IS - 1 SP - 379 EP - 388 PB - FU Berlin ER - TY - JOUR A1 - Vollmer, Michael T1 - Limitations of the eye and how to overcome them JF - Journal of Physics: Conference Series N2 - Human eyes have spatial, temporal, and spectral limitations which impose constraints on our perception. With appropriate optical devices and cameras, the limitations can be easily overcome. As a consequence, a huge variety of physical phenomena can be made accessible for teaching. Y1 - 2024 U6 - https://doi.org/10.1088/1742-6596/2750/1/012001 VL - 2750 IS - 1 SP - 1 EP - 10 ER - TY - JOUR A1 - Vollmer, Michael T1 - Nachtsicht ins All mit dem bloßen Auge: Sag mir, wie weit die Sterne steh'n JF - Physik in unserer Zeit Y1 - 2025 U6 - https://doi.org/10.1002/piuz.202501751 VL - 2025 SP - 2 EP - 10 PB - Wiley ER - TY - JOUR A1 - Vollmer, Michael T1 - Naked eye celestial objects and phenomena: how far can we see at night? JF - European Journal of Physics N2 - 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. Y1 - 2025 U6 - https://doi.org/10.1088/1361-6404/adbf74 VL - 46 IS - 3 PB - IOP Science ER - TY - JOUR A1 - Vollmer, Michael T1 - How far can we see at day? JF - European Journal of Physics N2 - 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. Y1 - 2025 U6 - https://doi.org/10.1088/1361-6404/adc4a0 VL - 46 IS - 3 PB - IOP Science ER - TY - JOUR A1 - Vollmer, Michael T1 - How many stars appear colored to the naked eye? JF - Applied Optics N2 - Naked eye studies of the clear night sky reveal that a certain percentage of all observable stars can be perceived as having color. Subjective estimates differ widely, ranging from just a few to a maximum of above two hundred. Explanations are based on the emission spectra of the stars, which are modified by interstellar dust clouds, the Earth atmosphere, and mostly the inverse square law. Color changes occur not only for variation of the star’s angular elevation above the horizon, but as well for decreasing nighttime sky brightness due to the transition from photopic via mesopic to scotopic vision. The maximum number of stars showing color to the naked eye depends on star illuminances on Earth and the background sky luminance. The limit of observing color is found to correspond to apparent visual magnitudes around , defining the number of colored stars. This also means that naked eye perception of stars with color is only possible for a certain star distance range, which is well below the maximum naked eye visual range of stars. Y1 - 2026 U6 - https://doi.org/10.1364/AO.580635 VL - 65 IS - 9 SP - C27 EP - C37 PB - Optica Publishing Group ER -