The full moon has long been associated with any number of superstitions. While links with lunacy, violence, fertility, disasters, and the stock market have been thoroughly debunked, the possibility of a causative role in some arenas still remains a possibility. A lunar ranging study carried out using reflectors has long contended with the "Full-Moon Curse", a near-total fading of reflected signals during the full Moon. This Curse is real, and has now been explained.
Lunar ranges have been collected for decades, most recently by astronomer Tom Murphy's group at UC San Diego, who is using these data to carry out a stringent test of general relativity. Lunar ranging works by sending laser pulses from the Earth to the Moon and back, timing the duration of the round trip.
The observations are now carried out using a 3.5 m (140 in) telescope at New Mexico's Apache Point Observatory. Twenty 532 nm laser pulses, each having an energy of 115 mJ and a duration of 100 ps, are directed each second through the telescope onto the lunar surface. The pulses then strike retroreflectors left on the Moon by Apollo astronauts and on a Soviet lunar rover. These optical prisms precisely direct reflected light back along the path on which it arrived; that is, back to the original telescope where their arrival is timed.
The time required for the round trip can be measured to within a few picoseconds, allowing the distance to the Moon to be measured with a precision of about a millimeter (0.04 in). The level of precision is remarkable, considering that only one photon, on average, is detected in each return pulse 13 roughly 1 in 100 quadrillion photons sent from the telescope to the Moon.
In short, a very difficult experiment is being carried out brilliantly. Then appeared the Full-Moon Curse. On the night of the full Moon, the strength of the returned signal drops roughly tenfold. Not just once; the drop follows the lunar phases month after month.
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