What is Sky?
[[File:Trees-sky.jpg|thumb|The daytime sky with [[Tree|trees]].]] [[File:TrafalgarSquareEvening.jpg|thumb|Sunset in [[London]].]] [[File:Twilight subcategories.svg|thumb|Colors of the sky at different times.]] The '''sky''' is the appearance of the [[atmosphere]] around the surface of the planet from our point of view. We see many objects that are actually in space such as the Sun, the Moon, and stars because they are in the sky. On a clear day the sky appears [[blue]]. ==Physics== At night, it appears from very dark blue to black. The deepness of the blue increases as we look toward the [[horizon]], and up to the point above us. The sky, which is made up of gas [[Molecule|molecules]], is blue because of the random scattering of sunlight by the molecules. ===Rayleigh scattering=== [[Rayleigh scattering]] defines the amount of scattering of [[light]] rays. [[Blue]] light scatters much more than [[red]], which is why the sky appears blue on a clear day. Depending on the time of day, the sky may appear different colors. At [[sunrise]] or [[sunset]], the sky may appear red, [[Orange (color)|orange]] and other colors depending on how low the sun is and how close it is to night. <ref> * {{cite journal|last=Tyndall|first=John|date=December 1868|title=On the Blue Colour of the Sky, the Polarization of Skylight, and on the Polarization of Light by Cloudy Matter Generally|journal=[[Proceedings of the Royal Society]]|volume=17|pages=223–33|bibcode=1868RSPS...17..223T|doi=10.1098/rspl.1868.0033|jstor=112380|doi-access=|s2cid=121593427}} * {{cite journal|author=Lord Rayleigh|date=June 1871|title=On the scattering of light by small particles|journal=[[Philosophical Magazine]]|volume=41|issue=275|pages=447–51}} * {{cite journal|last=Watson|first=J. G.|date=June 2002|title=Visibility: Science and Regulation|url=|journal=J. Air & Waste Manage. Assoc|volume=52|issue=6|pages=628–713|bibcode=2002JAWMA..52..628W|doi=10.1080/10473289.2002.10470813|pmid=12074426|doi-access=|s2cid=1078961}} * {{cite web|last=Gibbs|first=Philip|dat