Hey, everybody! Scott here, coming to you from six inches away from a fresh cup of coffee. I admit it; sometimes I like that cheap kind from the supermarket with the fake vanilla flavor. In fact, lots of the time. So, today Skywatch HQ and this post smell like a donut shop.
Today, and today only, well… for this month, it’s Dark Side of the Moon day! This only happens about thirteen times a year!
Nope, no Pink Floyd around here; I’m listening to Crowded House’s “Temple of Low Men” album as I write this, with some REM backing it up. A couple people have asked me recently why they’ve noticed the words “far side” rather than “dark side” being used when people talk about our nearest neighbor in the sky. For instance, in this post here from the other day and lots of other places around the Internet.
It breaks down like this. The same side of the Moon always faces the Earth. That’s because over the years, the Earth’s gravity has slowed the Moon’s rotation, it’s spin, so that one day on the Moon takes the same amount of time as one orbit around the Earth; about 28 Earth days. This might make you think the Moon doesn’t spin at all, but in order for it to keep the same side facing the us all the time, it needs turn to keep up with the trip around.
Let’s have a look at this.
There’s the Earth and the Moon at two different places in its orbit as seen from above the Earth’s north pole. The Sun is off to the right. Today, August 2, 2016 (can you believe it’s August already?), is to the right of the Earth. It’s the Moon’s “new” phase. The Moon is between the Earth and the Sun. So, all of the sunlight hitting the Moon falls on the side that always faces away from us. That side is farther from us, we call it the “far side,” but it is most certainly not dark at the moment.
Just as on Earth, when sunlight hits a given spot, we say it’s daytime. The sunlit side of the Moon is its day side, no matter which side it is. The dark side of the Earth? That’s right, it’s the side that faces away from the Sun; where it’s night. As I write this, places like Tokyo, Beijing, Perth and Jakarta are on the dark side of the Earth.
The dark side of the moon changes from day to day. Today, at new moon, it’s the side facing the Earth; what we call the near side. Nighttime on the Moon is facing us today. The Moon is up in the sky now, all day today. You’d be able to see it gloriously not shining at you if not for the fact that you can’t see the new moon at all because it’s washed out, hidden away by the Sun’s glare.
In about two weeks, when the Moon has made its way halfway around in its orbit, the Sun will be lighting up only its near side, the side that always faces us. This is what we see as a gorgeous glowing ball in the nighttime sky and call the full moon (August’s is nicknamed the “Sturgeon Moon”). Full Moon is the only time calling the far side of the moon the dark side is truly correct. The truth is, the far side and the near side have equal amounts of light and darkness.
If you look a little closer at the drawing, you’ll see that the far side of the Moon is to the right today, at new Moon, and to the left at full Moon. In order for that to be, the Moon must have turned half way as it made its way half way around in its orbit.
Over the next couple of weeks we’ll see more and more of the Moon as it moves toward full. In between we see the different sizes and shapes of the Moon’s phases that we all know and love. For today, and for the next couple of days, enjoy seeing the dark side of the Moon. During these early phases, the waxing crescent ones, you’ll be able to see it more easily.
Clear skies, everyone!