BOSTON (WHDH) - You’ve probably heard the saying “once in a blue moon.” Well, depending on your definition, that happens tonight.
In Shakespeare’s day, “once in a blue moon” meant something rare or absurd. Since the 1940s, “once in a blue moon” has come to mean the 2nd full moon in a month. Since there are 29.5 days between each full moon, it is pretty rare to get 2 full moons in a single month. Somewhere in between Shakespeare’s time and modern times, there was a definition that Sky and Telescope refers to as the “Maine rule” for blue moons which states that a blue moon is the 3rd full moon in a season that has 4 full moons. There is another full moon just hours before the summer solstice next month. That will be the fourth full moon this spring so tonight’s full moon is the “blue” one.
Why is the 3rd full moon the blue moon? Well, the simplified answer is that each full moon of the season is assigned a name. Generally the May full moon is called the “flower moon” or the “corn planting moon.” But, if there are 4 full moons is a season, the only way that the names of the other full moons line up with the coordinating season is to call the 3rd full moon the “blue” one. Otherwise the “corn planting” moon might rise at a time that wouldn’t be appropriate for planting corn. Make sense? Not really!?! Just know this, since there is about a month in between each full moon, it is pretty rare to get 4 full moons in a season that has only 3 months. It won’t happen again until winter of 2019.
The moon won’t actually look blue. According to NASA the key to an actual blue moon is having lots of particles in the air that are slightly wider than the wavelength of red light (0.7 micron) and not much else. In other words, you need particles that are big enough to scatter out red and yellow light, but allow blue and green light through. This is rare, but volcanoes sometimes spit out such clouds, as do forest fires. The moon apparently appeared blue or green for years after the Indonesian volcano named Krakatoa erupted in 1883. More recently, there were reports of blue moons caused by Mt. St. Helens in 1980 and Mount Pinatubo in 1991. In 1950, smoke from a large wildfire in Alberta, Canada caused the moon to look blue in the eastern United States and even in England a few days later. So far, I personally haven’t seen any reports of an actual blue moon from the current wildfires burning in Alberta.
Either way, you won’t be able to see this blue moon. It will be too cloudy. Again, don’t feel like you are missing out because in reality, this “blue Moon” won’t look any different than any other full moon or any different than it looked early this morning. However, coincidentally, the not really blue moon will appear near the actually red Mars, forming a near perfect square with Saturn and Antares Saturday evening. That is something that would have otherwise been worth seeing.
Unfortunately for astronomy lovers and sun lovers alike, clouds take over late Saturday and stay with us for a few days. Will there be any rain from those clouds? Good question! This will be an ocean storm that passes to our south and east. The question is how far north does the rain get. Right now it looks like the best chance for rain will be between about 11pm Saturday night and 9am Sunday morning for the South Coast, the Cape and the Islands. Those areas might see a quarter of an inch of rain or more. The rest of us will see some spotty light rain if anything. Clouds stick around through Sunday. Late in the day there could be some showers in northwestern MA as some moisture wraps around the back side of the departing storm system.
Monday we will be in between two storm systems. That should give us a mix of clouds and some sun. The next storm system passes by on Tuesday along a track that should be similar to Sunday’s storm, so expect a similar pattern to the rainfall…more in southeast MA.
Boston should hit 80 degrees for the first time in 2016 on Wednesday!!! In fact, the rest of the week will be very summer-like. With some heat and humidity, we might see some pop-up, summertime variety, afternoon thunderstorms on Friday.
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