Once in a blue moon, I get a chance to talk about something uncommon in our earthly realm, something non-lighthouse. If you're only interested in lighthouses, stop reading this post now, though you'll miss some amazing lighthouse photos later in the blog. This entry is about the moon, which I think of as a huge natural lighthouse. Sailors of old used it for navigation. If you've ever tried to calculate a lunar position, you know about this.
I’ve always regarded the moon as a giant lamp in the heavens, a lunar lighthouse of sorts. And being an avid amateur astronomer, I spend a good deal of my time watching the sky, day and night. It's a wonderful, free playground up there. Go check it out.
|Hormbersund Lighthouse, Norway|
In this blog, I’d like to encourage you to enjoy a free celestial show coming up January 31st. An eclipse and a blue moon. Yes, there really is such a thing as a blue moon. It doesn’t just apply to lovesick rock and roll singers and a colorful mixed drink of curacao and gin. And it rarely occurs alongside a total lunar eclipse. But in two weeks it will put on an extraordinary show. (More about the eclipse later.)
A blue moon is an authentic astronomical event, Can the moon be blue? Yes, in several ways. Certain atmospheric conditions, such as smoky air from forest fires, can make the moon appear blue. So can dust from a big volcanic eruption.
In 1883, when the Indonesian volcano Krakatoa blew its top in a blast equaling the force of 100-megaton nuclear bomb, dust circulated in the atmosphere for several years, causing glorious blue moons. The 1980 eruption of
and the 1991 blast from Mt. St. Helens Mt. Pinatubo caused
a similar spate of blue-tinted moons.
Why? Well…the particles of dirt from such catastrophic events are just the right size, each about 1 micron wide (one millionth of a meter), to scatter all the colors of light except the blue wavelengths. This gives the lunar face a bluish cast.
|Barnegat Lighthouse, New Jersey|
But smoke and volcanic ash won’t be the cause of the January 31 blue moon, at least we hope it won’t. Instead, the traditional and more predictable definition of blue moon will apply. January 1st was the first full moon of the month, the Wolf Moon, and January 30 will bring another full moon, the Snow Moon. Two full moons in one calendar month mean the second one is called a blue moon.
Why? Not because of color. The moon won’t have a blue hue on January 31. Instead, this moon is “blue” because it’s a rare occurrence. It only happens “in a blue moon.”
Usually, only one full moon occurs in a month, since about 29.5 days are required for the moon to show all of its phases. Months with 30 days are less likely to experience blue moons than those with 31 days. February never has a blue moon, even in a leap year, because it is always shorter than the moon’s phase period. March 31, 2018 also will have a blue moon, so if you miss the January blue moon, you can see the phenomenon again in March.
Calendrical blue moons occur roughly every 2.7 years or once in 33 full moons. This adds up to about seven blue moons during the Metonic Cycle, a predictable period of 235 lunations (moon cycles). At the beginning of this cycle, the full moon is at a set point in its orbit around Earth. It then orbits 235 times before it arrives back at that exact same point 18.6 years later.
The cycle was named for Meton of Athens who discovered it in the fifth century B.C.E. The ancient Greeks were attuned to anything cyclical, which they felt had significance in political and social affairs. The Greek calendar was different than the one we use today, but it had blue moon months. Public monuments in Athens were inscribed with the Metonic dates, and important events, such as the Senate convening, were scheduled according to the full moon schedule.
|Jupiter Lighthouse, Florida|
Also important in Greek affairs was the time known as a “lunar standstill” when the moon experiences a slight and very slow wobble in its motion and allows observers to view a bit of its dark side. (We see only one side of the moon throughout its phases. Standstills reveal small slices of the unseen side. The moon really does not stand still at this time; rather it reaches a high or low point in its orbit for a brief time and appears to be stationary.)
If all this lunar language sounds complicated and brain boggling….well, it is. Lunar motions are among the most challenging celestial gyrations to understand. Even scientists admit the moon can be mysterious. Isaac Newton once commented that calculating lunar positions made his head ache. Thankfully, computers now do the number crunching.
A better appreciation of moon melodramatics might be achieved by simply recognizing the duality and beauty of our moon. Its face and positions in the heavens are ever-changing and sometimes surprising, as when a blue moon occurs, or we get a peek at the edge of the dark side, or we get a lunar eclipse. Yet the moon is still a predictable friend in the night sky and a timepiece of sorts.
|Split Rock Lighthouse, Minnesota|
Finding the blue moon on January 31 will be easy. Head for some open space with a clear eastern horizon (the ocean would be perfect), and take some time to observe the moon’s rise over the horizon. Moonrise will occur in the northeast a few minutes after sunset. (A good rule to remember is that full moons rise along the eastern horizon at approximately the same time the sun sets in the opposite direction.) The moon’s bright light will wash out the dim surrounding stars of its host constellation, Virgo, the maiden.
As if a blue moon isn’t enough, we’ll also be treated to a total lunar eclipse on January 31. In 2017, we were treated to a solar eclipse, when the moon moved in front of the sun. A lunar eclipse occurs when the shadow of the earth passes over the moon. Not everyone will see the January 31 lunar eclipse. Here in Connecticut, where I live, only the earliest part of the eclipse will be seen. My daughter, in Seattle, will see much more. Check this website to learn more about what you’ll see at your location and when. https://www.timeanddate.com/eclipse/lunar/2018-january-31
And while you’re watching this rare celestial show, consider the regularity and reliability of the gears that keep our universe ticking. The moon is only one cog in the grand cosmic wheel, but it’s an astonishingly predictable one.
|Point Wilson Lighthouse, Washington|
Many lighthouses that are open to the public offer full moon climbs. Check for one in your area.
|Have fun with your camera! Above is Hillsboro Inlet Lighthouse in Florida and below is Marblehead Lighthouse in Massachusetts.|
|Nubble Lighthouse, Maine|