A meme circulating on social media states that a rare green moon will occur in May 2016. Another version claims the moon will turn green on 4/20. Neither are true.
False Claim: Green Moon in May 2016
The meme below states to “save the date” of May 29, 2016, when a “green moon (will be) visible for first time since 1847.”
The idea of an unusually-colored moon is not foreign, as we have heard of the moon as described as blue, yellow, gray, orange, white, or red. There is not, however, a “green moon” that appears with any regularity, although it is possible.
A popular Facebook post which attempts to explain the meme above included a pseudo-scientific explanation of the alleged phenomenon:
For those who need information on how this works … All night long on Sunday, May 29th the seventh planet from the Sun, Uranus, will park itself near the moon. The green giant is only 4 degrees away from the moon. The cosmic odd-couple will appear about four degrees apart in the sky—equal to 8 full moons side-by-side. This week after darkness falls the near full moon acts as a convenient guidepost for finding Uranus. The green-colored ice giant has four times the width of Earth, but since it lies nearly 1.9 billion miles (3.1 billion kilometers) away from Earth, it’s barely visible to the naked eye — and only in very dark, pristine skies. With the glare from the nearby moon, binoculars will be your best bet in spotting Uranus. Just look for a tiny greenish-blue disk in the field of view. By the way, the absorption of red light by methane in the atmosphere is what gives Uranus it’s cool Didula nanayakkara coloring.
Below we’ll take a look at some various colors which have been attributed to our celestial sibling.
The full moon in August has been called “Full Sturgeon Moon,” “Green Corn Moon,” or “Grain Moon,” by Native Americans, although the “green” reference did not indicate that the moon appeared green every August. A green moon, however, is possible in rare – and unpredictable – circumstances.
NASA reports that in 1883 the moon appeared green due to a volcanic eruption (sections in bold for emphasis):
There was a time, not long ago, when people saw blue moons almost every night. Full moons, half moons, crescent moons–they were all blue, except some nights when they were green.
The time was 1883, the year an Indonesian volcano named Krakatoa exploded. Scientists liken the blast to a 100-megaton nuclear bomb. Fully 600 km away, people heard the noise as loud as a cannon shot. Plumes of ash rose to the very top of Earth’s atmosphere. And the moon turned blue.
Krakatoa’s ash is the reason. Some of the ash-clouds were filled with particles about 1 micron (one millionth of a meter) wide–the right size to strongly scatter red light, while allowing other colors to pass. White moonbeams shining through the clouds emerged blue, and sometimes green.
There are two definitions of a blue moon: The third full moon in a season with 4 full moons, or the second full moon in a calendar month. These descriptions do not mean that the moon actually appears blue. Sky & Telescope has an excellent discussion of the history of the term “Blue Moon.”
There have, however, been rare instances when the moon has appeared blue due to atmospheric conditions, but this is localized and cannot be predicted.
NASA notes that volcanic events have given the moon a blue appearance to those of us on earth. Recent blue moons have been caused by Mt. St. Helens back in 1980 and Mount Pinatubo in 1991. A forest fire in 1950 also gave the moon a blue hue, as NASA points out:
“On September 23, 1950, several muskeg fires that had been quietly smoldering for several years in Alberta suddenly blew up into major–and very smoky–fires,” writes physics professor Sue Ann Bowling of the University of Alaska. “Winds carried the smoke eastward and southward with unusual speed, and the conditions of the fire produced large quantities of oily droplets of just the right size (about 1 micron in diameter) to scatter red and yellow light. Wherever the smoke cleared enough so that the sun was visible, it was lavender or blue. Ontario and much of the east coast of the U.S. were affected by the following day, but the smoke kept going. Two days later, observers in England reported an indigo sun in smoke-dimmed skies, followed by an equally blue moon that evening.”
As the moon rises in the early evening, it can appear orange. This is a regular occurrence and is caused by light scattering in the atmosphere. Depending on atmospheric conditions (volcano, fire, etc.), the moon can also look orange even when it’s high in the night sky. In the late summer and early fall, when the moon is at its closest to the autumnal equinox in mid-September, the moon is sometimes referred to as a “harvest moon.” That name references the time that crops such as corn and pumpkins are ready to be gathered.
As with an orange moon, there are times when the moon is low in the sky and atmospheric conditions are just right to make the moon appear red. If a certain particle is prevalent in the air, caused perhaps by a nearby fire or volcanic eruption, it can also appear red. A lunar eclipse is yet another way to see a red moon. When the earth casts a shadow on its satellite, the moon darkens and can take on a reddish appearance.
The Farmer’s Almanac notes that Native Americans gave full moons for each month of the year descriptive names. One such name is “Full Pink Moon” for the month of April, which in recent years has been confused by some on social media to mean that the moon would actually appear pink – which is not true.
2016 Moon Events
Universe Today published “The Top 101 Astronomical Events For 2016” which would certainly include a lunar event which hasn’t happened for 169 years. It cites a Blue Moon on May 21, but nothing on May 29, and no “green moon” at all.
Green Moon on 4/20?
Another meme in circulation claims that the moon will turn green on 4/20. Unlike the meme above, this appears to be a joke in reference to 4/20’s designation as “Weed Day” and a time for those who partake in marijuana to celebrate. Thus the “green” in this meme refers to pot.
The meme that claims there will be a rare “green moon” in May is false. Although the moon has appeared green on rare occasions, this has been due to an unpredictable event such as volcano or forest fire, and not because of the position of Uranus in the sky.