Light Color and Atmospheric Light, Color, and Atmospheric Optics

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Light Color and Atmospheric Light, Color, and Atmospheric Optics

Light, Color, and Atmospheric Optics Chapter 19 April 28 and 30, 2009 Colors • Sunlight contains all colors (visible spectrum) Wavelength Ranges in µm UV-C: 0.25 - 0.29 UV-B: 0.29 - 0.32 UV-A: 0.32 - 0.38 Visible: 0.38 - 0.75 Near IR: 0.75 - 4 Mid IR: 4 - 8 Longwave IR: 8 - 100 Colors • If object is white then all colors are reflected • If object is red then only red is reflected and all others are absorbed From Malm (1999). Introduction to Visibility Blue Skies and Hazy days • Selective scattering – Scattering depends on wavelength of light • Rayleigh scattering – Very small particles, gases • Mie scattering – Particles the size of wavelength of visible light • Blue haze • Some particles from plants: terpenes, α- pinene Blue Ridge Mountains • Blue haze caused by scattering of blue light by fine particles Creppyuscular Rays • Scattering of sunlight by dust and haze produces white bands Selective Scattering: Sunset • Notice the effects of scattering on color as sunlight penetrates into the atmosphere Twinkling, Twilight, and the Green Flash • Light that travels from a less dense to a more dense medium loses speed and bends toward the normal, while light that enters a less dense medium increase speed and bends away from the normal. • Apparent position, scintillation, and green flash all depend of density variations in the athtmosphere • Scintillation also indicates the amount of turbulence in the atmosphere Bending of Light Paths from Atmosphere Green Flash • Green flash at top may be seen under circumstances of very cold (dense) air near the surface rapidly changing to warmer (less dense) air aloft Mirages •Miraggyges are caused by refraction of light due to strong density differences in atmospheric layers usually caused by strong temperature differences. An object appears to be displaced from true position. Inferior Image Formation IfInferi or: down to groun d Superior Image Formation Superior: up into air Example: Fata Morgana –Fairly uniform surface is transformed into one of vertical walls and columns with spires –Usually in polar regions with warm air over a cold surface. 22° Halo Formation of 22° and 46° halos Effects of Dispersion Sundogs Sun Pillar Ice Crystal Shapes http://www.atoptics.co.uk/halo/common.htm Rainbows • Face falling rain with sun at back, water droppps disperse li ght • Primary and secondary Rainbow from raindrops Other Single Particle Effects Results from geometrical optics, snell’s law of refraction for drops of a few mm in diameter.

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Why Doesn't the Sky Turn Green?
Why Doesn't The Sky Turn Green? Rushi Shah 09 November 2015 I was leaﬁng through the US Army Corps of Engineers' Manual on Remote Sensing and learned about how Rayleigh scattering creates blue skies during the day and redish-orange sunsets. Well, everybody knows about blue skies and red sunsets, was the title just click-bait, you ask? No, but I'll get to that. 1 The Basics of Rayleigh Scattering Let's start with this whole Rayleigh scattering thing. Basically the idea is that particles in the atmosphere (like Oxygen and Nitrogen particles) scatter rays of light as they enter the atmosphere. How much the light is scattered is heavily dependent on the wavelength of the light. Remember how ROY-G-BIV represents the colors of the rainbow (and thus the spectrum of visible light)? Well that spectrum of light starts with long wavelength rays (reds, oranges, and yellows) and ends with short wavelength rays (blues, indigos, and violets). 1 The amount of light that is scattered (denoted with the variable I) is highly inversely proportional to the wavelength of the light (denoted with the greek letter ). Put simply, as the wavelength goes down, the light waves are scattered more quickly. 1 I / λ4 When sunlight hits the earth directly during mid-day, it travels through a small amount of atmosphere, and thus we see the wavelengths of light that are immediately scattered. Based on the equation above, the blues, indigos, and violets would be scattered ﬁrst (and they blend together into the blue sky we see). As the sun sets, it goes through more and more particles to reach us.
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Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Reports 2018 Evaluating the Effectiveness of Current Atmospheric Refraction Models in Predicting Sunrise and Sunset Times Teresa Wilson Michigan Technological University, [email protected] Copyright 2018 Teresa Wilson Recommended Citation Wilson, Teresa, "Evaluating the Effectiveness of Current Atmospheric Refraction Models in Predicting Sunrise and Sunset Times", Open Access Dissertation, Michigan Technological University, 2018. https://doi.org/10.37099/mtu.dc.etdr/697 Follow this and additional works at: https://digitalcommons.mtu.edu/etdr Part of the Atmospheric Sciences Commons, Other Astrophysics and Astronomy Commons, and the Other Physics Commons EVALUATING THE EFFECTIVENESS OF CURRENT ATMOSPHERIC REFRACTION MODELS IN PREDICTING SUNRISE AND SUNSET TIMES By Teresa A. Wilson A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY In Physics MICHIGAN TECHNOLOGICAL UNIVERSITY 2018 © 2018 Teresa A. Wilson This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Physics. Department of Physics Dissertation Co-advisor: Dr. Robert J. Nemiroff Dissertation Co-advisor: Dr. Jennifer L. Bartlett Committee Member: Dr. Brian E. Fick Committee Member: Dr. James L. Hilton Committee Member: Dr. Claudio Mazzoleni Department Chair: Dr. Ravindra Pandey Dedication To my fellow PhD students and the naive idealism with which we started this adventure. Like Frodo, we will never be the same. Contents List of Figures ................................. xi List of Tables .................................. xvii Acknowledgments ............................... xix List of Abbreviations ............................. xxi Abstract ..................................... xxv 1 Introduction ................................. 1 1.1 Introduction . 1 1.2 Effects of Refraction on Horizon .
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The Color of the Sky
Atmospheric and Climate Sciences, 2012, 2, 510-517 http://dx.doi.org/10.4236/acs.2012.24045 Published Online October 2012 (http://www.SciRP.org/journal/acs) The Color of the Sky Frederic Zagury Department of the History of Science, Harvard University, Cambridge, USA Email: [email protected] Received June 9, 2012; revised June 30, 2012; accepted July 9, 2012 ABSTRACT The color of the sky in day-time and at twilight is studied by means of spectroscopy, which provides an unambiguous way to understand and quantify why a sky is blue, pink, or red. The colors a daylight sky can take primarily owe to Rayleigh extinction and ozone absorption. Spectra of the sky illuminated by the sun can generally be represented by a a 1 4 generic analytical expression which involves the Rayleigh function R e , ozone absorption, and, to a lesser 4 extend, aerosol extinction. This study is based on a representative sample of spectra selected from a few hundred ob- servations taken in different places, times, and dates, with a portable fiber spectrometer. Keywords: Sky Color; Rayleigh Extinction; Ozone; Aerosols; Radiative Transfer; Spectral Analysis 1. Introduction agree that the blue color of the sky in day-time is due to Rayleigh scattering and that blue nuances at twilight, Two major causes of the extinction of light by the at- when the sun is low on the horizon, require an additional mosphere, extinction by air molecules (nitrogen mainly) ozone absorption [11-16]. A conclusion that Wulf, and ozone absorption, were discovered in the second half Moore, and Melvin [17] had already reached in 1934 of the XIXth century when scientists1 questioned why the from what may be considered as the very first published sky is blue.
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446 NATURE [MARCH 22, 1930 of the Higher Hydrate, the Function of Which May Or Clouds Lying Low Above the Ocean Or Mountains
446 NATURE [MARCH 22, 1930 of the higher hydrate, the function of which may or clouds lying low above the ocean or mountains. possibly be filled by other solids, isomorphous or All but one of the flashes at sunrise have been seen otherwise, furnished by dust, promotes the reaction. from Westwood Hills as the sun has risen over the Dust may even fumish particles of salts that are Baldwin Hills and other elevations east and south deliquescent under the conditions of the experiment, east ; while one of the most beautiful was seen from a thus making possible hydration of the salt studied peak on the eastern rim of Death Valley. by water in the liquid phase. One could not, there The observations of these beautiful but variable fore, hope to observe, nor does one observe, the phenomena have been very numerous. Usually no behaviour mentioned above if starting nuclei, fumished record has been kept ; but in the 32-day interval by dust, were thickly spread over the surfaces of the Aug. 20-Sept. 20, 1928, I witnessed the flash at Slill· crystals of the lower hydrate. In such a case, the set 13 times ; and I am confident that I have since induction period would be lacking and the rate of seen a greater number of sunset and sunrise flashes reaction a steadily diminishing one as the zone of in an interval no greater. In the 32 days referred to, reaction progressed, with diminishing area, toward fogs and clouds interfered on 9 days ; the hack the centres of the crystals ; and this has been the ground of sky was too bright on 3 days ; observations common observation in the past.
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