September 26, 2007

The Harvest Moon

Tonight the reddish orange color of the Harvest Moon will be upon us yet again. The full moon nearest the autumnal equinox makes the moon's light last well into the night, allowing farmers some much needed light to harvest there fall crops.
The atmosphere reduces visible light on celestial objects near the horizon, which is why they are always brighter overhead. The atmosphere scatters blue light in the spectrum causing this. This reduction of blue light allows us to look at the setting sun, yet keeps us from looking into the sun during midday. The orange reddish color in the moon will be prevalent until the moon starts moving directly overhead away from the horizon at which point it will resume its normal white color.
The harvest moon often makes the moon look larger, yet this is an optical illusion. By simply taking pictures of the moon near the horizon and taking pictures of it in the sky and comparing the photos, the illusion will be revealed, assuming you use the same camera settings. There's quite a bit of heated debate as to which hypothesis of why this occurs is true.