MadSci Network: Astronomy

Re: why does the moon turn orange-yellow in the fall?

Date: Wed May 3 21:27:47 2000
Posted By: Tom Stickel, Grad student, Optometry, Indiana University School of Optometry
Area of science: Astronomy
ID: 955726938.As

  Interesting question.  Sometimes in the fall the moon really can look 
orange and yellow.  If you observe closely, though, you'll find that the 
in the fall, when the moon is right overhead, it looks pretty white.  And 
in the winter, when the moon is close to the horizon, it can look pretty 
orange.  Here's what's going on.
  The first thing that you have to understand is that there are different 
kinds of light.  Green light, for instance, is different than red light.  
Blue light is different than yellow light.  The main difference is that 
different colors of lights have different wavelengths.  Light travels in 
waves, and the distance from one peak of a wave to another is called the 
wavelength.  Blue light has a very short wavelength, and red light has the 
  The second thing to understand is that the air in our atmosphere acts 
like a filter.  It filters out short wavelength light, and scatters the 
short wavelengths around.  The short wavelengths are the blue ones. The 
greens, yellows, and reds come through.  That's why the sky looks blue. 
All the blue light is bouncing around the air before it comes down, so the 
sky looks blue.
  At night, when the moon is right overhead, it looks white.  White light 
is made up of all different colors of light, including blue.  When the 
moon is right overhead, it comes straight through the atmosphere, so not 
much of the blue light gets scattered.  But when the moon gets close to 
the horizon, it isn't coming at you straight on.  It's kind of slanting at 
us, and it's going through a lot more air.  The more air the white 
moonlight has to go through, the more chance for the short wavelength 
(blue) light to get scattered out.  The green light is pretty short too, 
so it gets filtered out too.  What's left is the red and yellow light.  
And that's why you only see the red and yellow light when the moon gets 
close to the horizon, and that's why the white moon looks red and yellow 
whenever it is about to rise or set. 
  Hope that helps a little bit.  At least now you know why the sky is blue 


Current Queue | Current Queue for Astronomy | Astronomy archives

Try the links in the MadSci Library for more information on Astronomy.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2000. All rights reserved.