Astronomy

Question

Why is the sky blue usually? Starr

Answer

Tiffany,<BR><BR>That's a very good question-- thank you for asking!&nbsp; Before I can answer your question, I have to explain a little bit about light and air.&nbsp;<BR><BR>As you probably know, sunlight is actually made up of many different colors.&nbsp; In fact, they are the colors in a rainbow: red, orange, yellow, green, blue, indigo, and violet.&nbsp;&nbsp;<BR><BR>The air that we breathe is made up of different gasses, like oxygen, nitrogen, and carbon dioxide.&nbsp; These gasses are&nbsp;made up of very small bits called molecules.&nbsp; They are so small that you can't see them, even with a microscope.<BR><BR>Ok-- now that we have that out of the way, I can answer your question.<BR><BR> <P>The blue color of the sky is due to something called Rayleigh (<EM>raw-lee</EM>) scattering.&nbsp; As the sunlight&nbsp;passes through the atmosphere overhead, the molecules in it scatter or spread the blue light in all directions, while letting the other colors pass straight through.&nbsp; This means when you look up, you are seeing the blue light that has been spread <STRONG>toward</STRONG> you from&nbsp;all over the sky.&nbsp; Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.&nbsp;&nbsp; Here's a picture that might help:</P> <P align=center><IMG alt="diagram explaining Rayleigh scattering" src=http://www.sciencemadesimple.net/img_sky/bluesky.gif" border=0><BR><STRONG><FONT size=1>Rayleigh Scattering <BR>(image courtesy of <EM>Science Made Simple</EM>)</P> <P align=left></FONT></STRONG>This also helps explain why sunsets are red.&nbsp; When the sun is low, all that blue light is scattered <STRONG>away</STRONG> from you, leaving mostly orange and red light.&nbsp; Here's another drawing to help:</P> <P align=center><IMG alt="image showing scattering at sunset" src=http://www.sciencemadesimple.net/img_sky/sunset.gif" border=0><BR><FONT size=1><STRONG>Why sunsets are red&nbsp;</STRONG></FONT><FONT size=1><STRONG> <BR>(image courtesy of <EM>Science Made Simple</EM>)</STRONG></FONT></P> <P>I hope this answers your question.&nbsp; Thanks again for asking.<BR><BR>Cheers,<BR><BR>Dennis</P> http://www.sky-watch.com/articles/skyblue.html http://www.exploratorium.edu/snacks/blue_sky.html http://science.howstuffworks.com/question39.htm Light<BR>Color<BR>Sky<BR>Rayleigh Scattering http://vrd.askvrd.org/services/answerschema.xml