You may have heard of the lunar tetrad of 2014-2015, four successive total eclipses, with no partial lunar eclipse in between. The second lunar eclipse of the tetrad occurred on October 7th and 8th of this year, and the third is scheduled to occur on April 4th of 2015. You may have also heard that it was a “blood” moon, because of the red tint the moon displayed during the lunar eclipse.
For the most part, the moon appears yellow because it reflects light from the sun and on occasion, the moon can appear red. One reason for the red tint is because of the billions of high density light particles in the air. When the atmosphere scatters sunlight, it is red light that gets scattered the least. A second reason for a red moon occurs when the moon is low in the sky, which means light from the moon has to pass through a larger amount of atmosphere. Blue and green light scatter to give off a reddish tint. Incidentally, it is this filtering of the green to violet portion of the light spectrum that gives us our blue sky during the day.
A third reason for the Moon to appear red occurs during a lunar eclipse. During an eclipse, the moon passes behind the Earth’s shadow and is no longer illuminated by the Sun. It is at this time that red light, filtered and refracted by Earth’s atmosphere, reaches the moon, turning the eclipsed moon its distinctive color. Depending on the amount of dust in the atmosphere at the time, that distinctive color can range from copper to deep red. If you were to take a look at the Earth from inside its shadow, you would see the entire planet glow red.
It’s not clear that a lunar eclipse has any effect on wildlife, although studies have shown that a full moon may have some effect on animal behavior. Increased moonlight can elevate nocturnal activity for some species and decrease it for others. In Australia’s Great Barrier Reef, moonlight triggers a collective mass-spawning event as corals release sperm and eggs in synchrony. During a full moon, the prolonged visibility of throat feathers permits owls to communicate more extensively, although some owls avoid activity during full moons. Wild dogs and cheetahs also increase their nocturnal activity during full moons, although lions may be less likely to hunt for lack of prey. Doodlebugs dig larger holes to trap prey during full moons, since the increase in light also increases the activity of their prey. Conversely, scorpions tend to be more active during the new moon, to catch prey that prefers darker nights.
Animals tend to adjust their behavior in response to changing light levels, although some behaviors follow more mysterious circadian rhythms controlled by the monthly lunar cycle. A deer’s reproductive cycle, for example, responds to the phases of the moon, peaking close to the second full moon after the autumnal equinox, also called the “rutting moon.” Increased light pollution, however, could be disrupting to these animal patterns by overshadowing the moon’s illumination.
For the bulk of the animal kingdom, the cycles of the moon are fairly mundane events. We, on the other hand, may always find something magical about a moon that, on rare occasions, appears to turn blood red.