Weekend Feature: Super Moon Over Earth Saturday Night


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The biggest and brightest full moon of the year arrives Saturday night, May 5, 2012 as our celestial neighbor passes closer to Earth than usual creating  a “supermoon'' –the closest and therefore the biggest and brightest full moon of the year. This month's perigee is the closest of any perigee in 2012, which vary by about 3 percent, because the moon's orbit is not perfectly circular. At 11:34 p.m. EDT, the moon will be about 221,802 miles from Earth. That's about 15,300 miles closer than average, which makes it appear about 14 percent bigger than it would if the moon were at its farthest distance, said Geoff Chester of the U.S. Naval Observatory. 

When the perigee moon lies close to the horizon it can create the famous "moon illusion" combines with reality to appear truly stunning and enormous. This  perigee moon, either rising in the East at sunset or dropping down in the West at sunrise might seem to make the moon appear so close that it almost seems that you could almost reach up and touch it. 

According to NASA, perigee moons are about 14 percent larger, and 30 percent brighter than apogee moons. For the best view of the supermoon, NASA has suggested viewing it when it’s lower in the sky.

According to Dr. James Garvin, chief scientist at NASA's Goddard Space Flight Center, a 'supermoon' is a situation when the moon is slightly closer to Earth in its orbit than on average, and this effect is most noticeable when it occurs at the same time as a full moon. So, the moon may seem bigger although the difference in its distance from Earth is only a few percent at such times.
It is called a "supermoon" because this is a very noticeable alignment that at first glance would seem to have an effect. The 'super' in supermoon is really just the appearance of being closer, but unless we were measuring the Earth-Moon distance by laser rangefinders (as we do to track the LRO [Lunar Reconnaissance Orbiter] spacecraft in low lunar orbit and to watch the Earth-Moon distance over years), there is really no difference. The supermoon really attests to the wonderful new wealth of data NASA's LRO mission has returned for the Moon, making several key science questions about our nearest neighbor all the more important.

The effects on Earth from a supermoon are minor, and according to the most detailed studies by terrestrial seismologists and volcanologists, the combination of the moon being at its closest to Earth in its orbit, and being in its 'full moon' configuration (relative to the Earth and sun), should not affect the internal energy balance of the Earth since there are lunar tides every day. 

The Earth has stored a tremendous amount of internal energy within its thin outer shell or crust, and the small differences in the tidal forces exerted by the moon (and sun) are not enough to fundamentally overcome the much larger forces within the planet due to convection (and other aspects of the internal energy balance that drives plate tectonics). Nonetheless, these supermoon times remind us of the effect of our 'Africa-sized' lunar neighbor on our lives, affecting ocean tides (and a visible aspect of how our planet is part of the solar system and space).

There are references, however, in scientific literature of a possible connection between full moons and seismic activity. The moon causes tides in the solid core of the Earth, just as it causes ocean tides. Most experts rule out the assumption that a close full moon might cause geologic activity to increase. 
But, it is pure speculation that a "supermoon" phase could cause tectonic plate shifts. We'll  test the theory during tomorrow's supermoon—which coincides with the moon’s closest point to Earth—and see if it bring more earthquakes and tsunamis.

You can check out this effect for yourself by first noting the times for moonrise and moonset in your region at http://www.usno.navy.mil/USNO/astronomical-applications/data-services/rs-one-year-us.

Image credit: With thanks to edrybczynskiphotos.com

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