WSET.com - ABC13Super (Red?) Moon by Lyndsay Tapases

Many of us were able to enjoy a rare sight this past weekend with the occurrence of a Super Moon on Saturday. We were fortunate enough to have clear skies that gave us a great view of Mother Nature's show. I wanted to address a question that I have received on a couple of occasions regarding the moon, and something that some of you may have even observed this weekend. The question is: Why does the moon sometimes appears red or orange in the sky?

Photo credit NASA/Bill Ingalls

The Super Moon rising over the Lincoln Memorial on March 19th, 2011.

The effect that causes the moon to sometimes appear red is the same effect that creates our blue sky. Our atmosphere is full of tiny gas and solid particles that scatter the sun's white light in different directions and influence the color that reaches our eye. This process is called Rayleigh Scattering. Each different color of light (which combined make up the white light from the sun) has a different wavelength. Colors with shorter wavelengths are absorbed more easily than colors with longer wavelength. Since the color blue has one of the shortest wavelengths, it is absorbed the most by molecules in the atmosphere. The blue light then gets radiated back out in all directions, thus creating a blue sky as observed from our view on the surface of the Earth.

Now back to the moon. Under normal conditions, when the air is clear and the moon is overhead, the moon reflects the white light from the sun, and appears white to us in the sky. The orange or red appearance most often occurs when the moon is close to the horizon and at a low sky angle. The moonlight has to pass through more atmosphere because of it's low angle and greater distance from the earth. Since the light is passing through more atmosphere, there are many more dust and pollutant particles to overcome. The colors with the shorter wavelengths (violets, blues, greens) tend to get refracted along the way by all of the dust and particles in the atmosphere. The longer wavelengths (red, oranges, yellows) are the ones that make it through. A red or orange moon can also occur because of unusually dusty, smoky, or polluted air. (And in case you were wondering, this is the same reason we experience beautifully colored sunrises and sunsets.)

I'll leave you now with a few pictures taken locally of the Super Moon this past Saturday. 

Photo Credits: Steven Owen