Once In a Blue Moon

You have probably heard the expression, “once in a blue moon.” People use that as a way of saying that something very rarely happens. For sky watchers, a blue moon has a different meaning. It refers to those times when a full moon occurs twice in the same month. That will happen tonight, Wednesday, August 30, 2023.

Although the “once in a blue moon” expression indicates something rare, astronomical blue moons are not all that rare. They occur on average four times per year, although they can happen as few as three times or as many as five times. The lunar cycle takes 29.5 days, so we usually have one full moon monthly. This year, we experienced a full moon on August 1, so we will see another one on August 31.

The “blue moon” title has nothing to do with its actual color. The Moon will appear white, yellow, or orange depending on its location and how much dust and other particles are in the air. If it is near the horizon, where its light has to travel through more of our atmospheric dust, it will appear white, yellow, or orange. High in the sky, it will look whiter unless there are perhaps pollutants, such as from wildfires.

In addition to being a blue moon, this full moon is also called a “super moon.” That is because it will be near its closest point to Earth. The Moon’s elliptical orbit averages nearly a quarter of a million miles from Earth. At the time of tonight’s full moon, it will be about 222,043 miles (357,344 km) from Earth. That means it will be the biggest and brightest full moon of 2023.

Despite people calling it a blue supermoon, it will not appear “blue,” and you may not think of it as incredibly “super.” It will be slightly bigger and brighter than other full moons this year, but you may not be extremely impressed. If you see it near the horizon, where it appears with buildings or trees, it will look more prominent compared to when you see it high in the empty sky. That is called the “moon illusion” and happens all the time, not just once in a blue moon.

So enjoy seeing tonight’s super blue moon, and thank God it’s there. Without it, we might not be here either. Our Moon is always “super,” as we have said many times. You can read more about that HERE, HERE, HERE, HERE, HERE, and HERE.

— Roland Earnst © 2023