Astronomer Mark Thompson explains why, on Wednesday, a lunar eclipse is set to dazzle night skies (but not in the U.S., sadly)
On the 20th Sept. 331 B.C., before the Battle Of Gaugamela between Alexander III of Macedon (Alexander The Great) and Emperor Darius III of Persia, an eclipse of the moon was observed.
Despite Alexander's army being considerably outnumbered, to astrologers of the time, the eclipse foretold Darius's defeat. As night fell on the battlefield, the eclipsed moon glowed a deep blood red, signaling blood would be spilled on that night, but not in Alexander's army.
As history shows, Alexander won the battle and it is thought the favorable forecast from astrologers gave his army the lift they needed (also, astrologers on the Persian side are rumored to have been bribed to foretell doom among Darius's men, impacting morale).
Throughout history there are countless examples of when eclipses have foretold doom. Significant events are chronicled to have taken place, shaping our past based on documented lunar eclipses. Nowadays, we know that these events simply coincided with the alignment of three celestial bodies, resulting in a stunning astronomical sight.
Lunar eclipses occur when the sun, Earth and moon sit in alignment and the Earth blocks sunlight from reaching the moon. Usually, of course, we can only see the moon because it reflects sunlight. But during an eclipse, the source of light is blocked and the moon's disk goes unusually dark.
However, the moon doesn't completely disappear since the gasses in our atmosphere act to bend some of the blocked sunlight, directing the red part of the solar spectrum back to the moon. Sometimes this has the effect of turning the moon a deep red, often blood red. The mechanism behind this phenomenon is called "Rayleigh scattering."