Having fallen sick the prior weekend, I was hard pressed to be dedicated in my efforts toward a speedy recovery while ruing the lost opportunity of posting a new article on the blog. A sudden cold, and the ensuing fatigue left me out of sorts; the origins of which could be traced back to a persistent cycle of late-night at work along with irregular sleep.
The past week has helped me recover, and now that I’m back, I would like to recapitulate on my original plans for a post dedicated to the lunar awesomeness coinciding with the final and initial weeks of January and February 2018.
The night of January 31st hosted a special treat for amateur and professional astronomers alike with three lunar events coinciding upon the occasion: a supermoon, a blue moon, and a blood moon.
Unfortunately, the weather in Edmonton was less than accommodating with a rapid slew of snowfall enveloping the city at January’s end, and resulting in quite the cloudy forecast on the night of the occasion.
While this was a mild disappointment, I drew delight by watching the video recordings of the event that were made available online the following morning. With that being said, what do astronomers mean when they use the terms supermoon, blue moon, and blood moon? Your friendly neighborhood astronomer is here to explain.
Simply put, the supermoon refers to a full moon or a new moon where the moon is at its closest distance to our planet in its orbit. This makes the moon appear slightly larger and brighter than usual.
The moon’s average distance is 382,900 km from Earth. To get some context, if we were to scale the Earth’s size or diameter (12,756 km) to that of a beach ball (16 inches), the distance from the Earth to the moon would be an equivalent of 40 ft. Thanks to its elliptical orbit, the moon tends to experience both a closest (perigee) and farthest (apogee) distance of approach to our planet.
Now, this doesn’t imply that a supermoon will occur every month as the moon’s orbit changes orientation as our planet revolves around the sun. Thus, a full or new moon won’t always happen at apogee or perigee. 12-13 full or new moons are possible every year, with 3-4 usually being classified as a supermoon. The most recent supermoon occurrence will be followed by another at the year on December 22, 2018. The closest supermoon of this century is set to occur in the relatively far future on December 6, 2052.
A blue moon refers to an additional full moon that appears among the months of a year. The term can refer to either the third of four full moons in a season or the second full moon over a month of the calendar year. The existence of the second definition is due to an erroneous parallel drawn by amateur astronomer James Hugh Pruett (1886-1955). Having misunderstood the measures for calculating the seasonal blue moon, Pruett would publish an article in 1946 in the Sky & Telescope magazine writing instead that the a blue moon was the second full moon in a month. The phrase “blue” has nothing to do with the actual color of the moon. Nevertheless, varying atmospheric conditions may cause the moon to take on a tinge of blue e.g. elevated fires or volcanic eruptions that may result in particles being spewed into the atmosphere resulting in the preferential scattering of red light.
Lastly, the blood moon refers to a lunar eclipse, when the moon passes directly behind our planet and into its shadow. This occurs only when the sun, Earth, and moon are aligned exactly or at least closely enough, with the Earth smack-dab in the middle.
This is also why a lunar eclipse can only occur on the night of a full moon. January 31, 2018 witnessed a total lunar eclipse, a perfect alignment that resulted in sunlight being completely blocked by the earth’s shadow.
The moon’s “color” is nothing more than the reflection of the sun’s light upon its surface. During a total lunar eclipse, the only light seen is refracted or bent through our planet’s shadow. This light is mainly of a “red” nature thanks to the scattering of its bluer spectrum (an opposite process to what may occur in a “literal” blue moon). Therefore, a total lunar eclipse is also called a blood moon as the moon takes upon a reddish color during the event.
So, what is so special about January 31, 2018?
Well, this was the first time in 152 years that these three lunar events coincided with each other making it a rare gem of a beautiful lunar display. Pretty much everyone in the UK missed out on the spectacle while those in the US, Asia, Australia, and Russia got to see the full eclipse. But not to worry, if you missed this lunar awesomeness of a super blue blood moon, the next one is up for grabs in 2037.
Finishing up with this astronomy treatise for today, unlike the 19 year wait in the case above, I hope to see you all soon again the following week with another interesting story to share.