Post by Joanna on Nov 30, 2014 2:40:44 GMT -5
The Moon and its Phases
The moon has intrigued humanity since we first craned our necks toward the heavens, but many still have questions about why Earth’s nearest neighbor appears as it does in the sky. The moon’s ceaseless celestial dance is indeed a complex one, taking it from dark and “new” to bright and full, then back again, over and over. Here are the answers to a few interesting questions that frequently come up regarding the phases of the moon:
How long does a full moon last? Probably not as long as you think. The actual moment of full moon – that time when the moon is opposite the sun in the sky – can be found in any almanac, and in many newspapers. We can therefore say the moon is officially “full” for just one minute! The full moon of March 27, 2012, for instance, occurred at 5:27 a.m. EDT (0927 GMT). In the very strictest sense, one minute before that time, the phase of the moon is a waxing gibbous; one minute after this time, it is a waning gibbous phase.
But is a full moon really ‘full’? Surprisingly, the answer is “no.” The disk of the moon can only appear 100 percent sunlit from Earth when it is diametrically opposite the sun in the sky. But that’s impossible, because at that moment the moon would be positioned in the middle of the Earth’s shadow and in total eclipse! In fact, in any month where there is no eclipse, there should be an ever-so-slight sliver of darkness visible somewhere on the lunar limb throughout those hours when the moon is passing through full phase.
Interestingly, people often refer to a full moon one, two or even three days before and/or after the actual full moon date. Yet close inspection will usually reveal the moon is not fully illuminated at these times, but is, indeed, gibbous, or slightly out of roundness.
Source: Joe Rao, Skywatching.