Caoimhín's Content

Today we are looking, once again, at the Moon. For a change, we are going to take a look mostly at the side of the Moon that we don’t normally get to see. The Chinese Space Agency, or the China National Space Administration, has recently landed a lander, Chang’e 6, on the Far Side of the Moon, what we often call the Dark Side of the Moon. This lander is part of a sample return mission, to collect samples from the Far Side of the Moon and return them to the Earth.

Before we focus in on that unfamiliar face of the Moon, we will have a quick look at the side facing us, the Earthward or Light Side of the Moon. About 8 months ago I made a video mostly about the Moon, and almost every video looking at the sky for a whole month will at least mention the Moon. I also discussed the Moon quite a bit in the context of the recent eclipses, both solar and lunar. Regardless, we’re going to have another quick look at it here. Given that we are so close to the solstice, it may be hard to see the Moon in true darkness, depending on your latitude. To make things a little simpler, in the video I turned off the atmosphere to ensure a pristine view. When we look at the Moon in the sky, it does look very bright, almost white against the black background of space. This is mostly an illusion, the surface of the Moon is really a grey colour, even those areas that look quite white and pale, they’re truly grey in colour. The darker areas are also a lot darker than they appear here.

One of the best known features of the Moon, at least the side we can see, are those dark areas, known as oceans, bays or seas depending on their size. The biggest dark region an ocean, the Ocean of Storms or Oceanus Procellarum. Probably the most famous sea is the Sea of Tranquility or Mare Tranquillitatis, where as only the smallest are called bays, such as the Middle Bay or Sinus Medii. The Sea of Tranquility is one that you can spot with your naked eye when looking at the Moon, as long as the Moon is full or if you’re looking at the correct Half Moon, the First Quarter Moon is when we see the half with the Sea of Tranquility. Different people imagine different things on the Moon, such as a Man on the Moon or a face, but I normally imagine a soccer player on the Moon. The Head is the Sea of Serenity, just to the left of the Ocean of Storms near the top. Under the head is the Body, followed by two feet (the Sea of Nectar and the Sea of Fecundity), with a football or soccer ball on the far left, the Sea of Crisis. The Body is the Sea of Tranquility, and looking for the shape of an imaginary football player is normally how I find it or point it out. Keep in mind that from the Southern Hemisphere the Moon appears the other way up, so the directions will be different.

From the Earth, we never get to see the other side of the Moon, so instead we are going to go to the Sun to look at the Moon from a different vantage point. The Sun is listed under planets when you’re looking for where to go in Stellarium. Changing planet, or star in this case, in Stellarium usually preserves your latitude and longitude, so we end up in the Northern Hemisphere of the Sun, where Ireland would be. To get a nice clear, simple, view we are going to relocate to the equator of the Sun. I’ll also need to remove the default landscape of lovely green grass, which of course wouldn’t be there on the Sun. Looking out into the solar system, on of the first objects you I notice is the comet 12P/Pons-Brooks, still on it’s way out of the inner solar system. Even moving to the Sun won’t change how the constellations appear. The constellations will look the same from every part of the Solar System, it’s only when you travel to other stars that the constellations could start to look different. The Earth should be visible from the Sun, however the Earth isn’t that as big as Jupiter or as close to the Sun as Venus and Mercury, so it might require a little bit of searching. Luckily, Stellarium can find it for you, as it can be a little strange to look for the Earth in the sky, when we’re normally on the Earth looking out into space. It is interesting to see the Earth hanging in space, in this case against the backdrop of the core of the galaxy. It requires a little bit of zooming in to resolve the Moon as a separate body to the Earth, but the view of the Moon is the reason we’re on the Sun. To begin with, it looks like a normal Full Moon, we happen to be looking at the side of the Moon facing the Earth. This is the only side we get to see, but as the Moon rotates, the normally out of view side turns to face the Sun. As we move through time it will continue to spin, giving us an alternating view of what we normally see and what we never get to see from here. As it does so, it will appear to twist and flip, but this is down to our position on the equator. Even on Earth, if you are trying to follow something as it passes directly over head, through the zenith, you would have to turn in order to keep it in view. The same thing is happening here, but it does look strange if your view moves when you are still.

More importantly, as the Moon rotates, we only see it fully illuminated. Although we get to see every part of the Moon, we do not see any phases at all. This is of course because we’re on the Sun, no matter what you look at, it will be fully lit up and that is a very important point when it comes to what we often call the Dark Side of the Moon. The Light Side of the Moon and the Dark Side of the Moon both get the same amount of sunlight. The Moon takes a month, roughly, to go around the Earth, so any given point on the Moon gets two weeks where it’s facing the Sun, and then another two weeks where it’s facing away. One exception to this would be deep polar craters which, as mentioned in a recent video, can be permanently dark at the bottom. From our perspective on the Sun, we can see the lunar landscape on the Far Side of the Moon, the Dark Side of the Moon, fully lit up in its daytime. It immediately looks very different to the surface of the Moon that we’re used to seeing. There’s no obvious big lakes or seas here, it’s a much smoother looking surface, at least when we’re seeing it fully illuminated from the Sun. As this is the Far Side of the Moon and we don’t get to see it from the Earth, we know a little bit less about it. Not much less but a little bit less. We’ve never been to the Far Side of the Moon, no crewed lunar missions have landed there, only on the near side of Moon, what we’d think of as the light side. The crewed missions to the Moon were able to bring back samples, and travel over a large area. Although no people have ever been to the Far Side of the Moon, there has now been a couple of landers and even a rover to the Far Side of the Moon thanks to the Chinese Space Agency. Rovers in particular are an important source of information about the Moon and planets such as Mars thanks to their ability to have a look around. Even landers are useful, as they can perform certain analyses of the surface while they are there. However, getting samples back to the Earth allows us to learn a lot more. There are always compromises when it comes to what instruments and tests to send into space, not everything will fit. Once a sample is here on Earth, there are a lot more options for how to study it. There are things we still don’t know about the Far Side of Moon, but bringing back samples should help. Samples have been returned from the Far Side of the Moon once before, by a Chinese sample return mission, Chang’e 5, and now another sample is on the way. Having a robot do this is of course safer, there is no crew to be in danger, and cheaper, but it hasn’t been an option until recently. One of the main reasons uncrewed missions are sent to space is because you don’t have to worry about bringing them back at all. Sending a craft into space with enough fuel to send itself back makes everything heavier and more expensive to launch in the first place. That’s before considering that an uncrewed mission will need to launch itself and at least partly guide itself back to Earth autonomously, something for which a human pilot used to be necessary. Now they are becoming such a viable option that hopefully we’ll have many more in the near future.

Our view from the Sun is a little limiting, in the Sense that we only see it perfectly full. To get a different view, we first go to Saturn. Saturn isn’t at opposition at the moment, so it isn’t directly behind the Earth. It will be soon, but right now it’s moving through our morning sky, and it will be in our midnight sky over the course of the next couple of months. Looking out from Saturn’s equator towards the Earth, you might miss the Rings. Being right at the equator of Saturn, we’re almost directly underneath the Rings, which makes them look like a very thin line. The Rings are only a couple of kilometers wide, they are much much broader from their inner to outer edge than they are thick from north to South. Zooming in on the Moon from Saturn unfortunately doesn’t reveal much, at least from this point in it’s orbit. Although Saturn isn’t at opposition yet, it was mostly seeing the Moon in almost complete or complete darkness, which of course makes it unobservable. It is also quite far away, making the Moon look small and obscuring most details. If Saturn were closer to being behind the Sun, the Moon would have appeared more illuminated, and Mercury is always close to the Sun.

Jumping to Mercury gives us a slightly different view. It’s certainly a slightly closer view, we are closer to Mercury than we are to Saturn. It is more similar to the view from the Sun, but with a little bit of shadow, which is what I had hoped to see from Saturn. It’s not quite as overwhelmingly bright as when we were looking at it from the Sun, and it’s also going to appear to move in a very different way. Moving day by day on Mercury means moving by Mercurian days, which are significantly longer than Earth days. That can cause things to jump around pretty wildly, so for this view moving through time over shorter scales made more sense. Just like our view from the Sun, we can see all sides of the Moon of the Moon from Mercury. This is almost always the case, it’s really just us here on Earth that are restricted to only seeing one side of the Moon. We get to see a little band of night time, visible on the Moon from Mercury, thanks to its position near, but not in line with the Sun. Just where day time meets night time, that is the terminator. Taht really is its name, the terminator is the line between daytime and nighttime, on the Moon and on any other planet . If you are standing in dusk or in dawn, you are on the Earths Terminator, if the Sun is just setting or rising for you then the terminator is moving past you. Thanks to the long shadows along the terminator, it becomes a lot easier to see the cratered texture of the Moon. As the line of the terminator moves across the Ocean of Storms you can see that there’s not too many craters, it seems pretty flat. This is generally true for all the darker regions. As the Moon continues to rotate, more craters will come into view, along the bottom of the side of the Moon that faces us. A mountain ridge-like ring is also visible, around the football or soccer ball, the Sea of Crisis, just in front of the Sea of Tranquility.

As the terminator moves across the Far Side of the Moon, there are loads and loads of small craters. the Far side of the Mon does have a slightly darker region, and there it is a little bit smoother just like the dark regions on the near side. It can be hard to see the craters on the Moon unless you’re looking at them along the terminator, which kept the Moon looking smooth in our view from the Sun. Now with the terminator to help us, we can definitely see that there’s a lot more craters, and those craters are old. The dark regions of the Moon are a newer surface, thanks to the Moon being punctured when there were still some liquid rock under the surface. That liquid rock spilled out and smoothed out the surface, covering up any of the craters. Craters can hold interesting information about whatever object crashed into the Moon and created the craters, so getting samples from the Far Side of the Moon might help us learn about the objects that crashed into the Moon. Those objects are often left over from the early solar system, so we might learn something about the composition of the early solar system by checking material on the Dark Side or the Far Side of the Moon,

Although I’m not explicit in the video about the successful return of samples form the Moon having happened, I would like to reinforce the point here. The Chinese space agency has recovered samples from the Far side of the Moon, which for all the reasons mentioned above, is quite a feat. Hopefully we will continue to learn more about the Moon, so that we are no longer in the dark about the Dark Side. If you enjoyed this little piece, then I hope you consider subscribing to this website and my YouTube channel, and I hope you will be back next time.