WHY DO THE SUN AND MOON LOOK BIGGER
WHEN THEY ARE NEAR THE HORIZON?
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METEOROLOGIST JEFF HABY
The distance from the surface to 300 mb averages 9,300 gpm. When the sun is directly overhead, radiation passes
through 9,300 meters of atmosphere between the surface and 300 mb. When the sun is at an angle, it must pass through
a greater length of the atmosphere before reaching the surface. When the sun is passing through the atmosphere at
a 45 degree angle, the radiation must pass through 13,000 meters of atmosphere between the surface and 300 millibars.
When the sun is passing through the atmosphere at a 5 degree angle, the radiation must pass through 107,000 meters
of atmosphere between the surface and 300 millibars.
The amount of scattering and refraction differential depends on how far the sun's radiation must pass through
the atmosphere. As the length of passage of light through the atmosphere increases, the amount of scattering
and the refraction differential increase. When the sun or moon are within about 10 degrees of the horizon,
they have the illusion of looking much bigger than they do higher in the sky and the coloring
looks different. This increase in scattering is also the cause of sun sets and sun rises giving
a red color on the horizon. Although the size looks different when close to the horizon, it is mostly an
illusion.
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