Observing the Moon, the best stuff to look at

Observing the Moon is a great way to come to terms with the fact that it will continue to ruin your Deep Sky observing objectives for the next few billion years. It’s a case of “if you can’t beat ‘em, join ‘em”. Fortunately the Moon does have some rather awesome things you can look at – it’s not just all craters and grey dust, though those craters are pretty spectacular. The first thing you will need is a good telescope, you want something so you can get up close and personal with the Moon. Binoculars are great (if they have a tripod) but to see the cool stuff you’ll need something with a bit more power. If you have a huge aperture telescope then you’ll need a Moon filter otherwise it’ll be too bright and you’ll get sore eyes.

My favourite crater is Clavius, it is huge and has a bunch of smaller craters inside of it. The crater is the third largest of the visible ones at 225km across and it’s in the Southern part of the Moon where some of the rugged highlands are – as opposed to the smooth Maria areas. You can observe this crater over a few days as it takes on a different character as the terminator moves further away. The craters inside Clavius all put on a different show of shadows which makes it a fantastic sight. A trick to see how good your telescope is, and how good the seeing is, to try and count how many of the smaller craters you can see on the floor of the main crater. Clavius is very old, it probably got formed during an impact about 4 bilion years ago and is one of the older formations on the surface.

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Clavius from the Lunar Reconnaissance Orbiter (Credit: NASA)

The next on the list of must see sights is the big crack/wall of Rupes Recta. This feature is also known as the Straight Wall, because it looks like one. It’s in the Mare Nubium and the feature is about 110km long with a width of 2-3km. Because of the way the sun illuminates the feature, it appears as a cliff but it is in fact a linear slope that isn’t all that steep at all. The sharp shadow of the features on the Moon are due to a lack of an atmosphere which helps to accentuate the illusion of this being a cliff. The feature is best viewed not far from the terminator as it’s much harder to see when the Sun is at a higher altitude above it.

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Rupes Recta from Apollo 16 (Credit: NASA)

Plato is my next favourite crater because of it’s super smooth floor that makes it standout so much from the surrounding terrain. The smoothness is because the crater floor was filled with lava shortly after impact. The crater is about 109km across and about 1km deep. The lava filled floor is quite fascinating as it means the crater doesn’t have the characteristic mountains that many other large craters have at the centre. Astronomers think the impact that caused the crater was about 3.84 billion years ago. When the angle of the Sun is low the crater really comes to life with amazing shadows from the wall being projected onto the crater floor. For the lunar imagers out there, a real challenge is to see how many of Plato’s cratelets you can capture on the floor of the crater, as many of them are smaller than 2km across.

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Plato from the LRO (Credit: NASA)

The next awesome sight is the Sinus Iridium which is a cool cross between a crater and lava plain or Maria. It’s part of the Mare Imbrium and the area around it is a delight to explore with the telescope as there’s some fascinating mountains all around and also some interesting deep craters as well. The feature was formed when a whole lot of lava spilled over the rim of the big crater that formed the circular art of the feature and flooded the crater floor – kind of similar to Plato, but not from the inside of the crater. This is a really beautiful feature and you can easily spend a lot of time admiring the different moonscapes that are visible.

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Sinus Iridium from the LRO and annotated by Wikipedia (Credit: NASA)

Th final in my selection of five features to have a look at on the Moon is the awesome crater Copernicus. This is a classic crater with a defined high wall and the central mountains. The wall is terraced showing that over time it has slumped and collapsed in parts. The crater is 93km across and has a depth of 3.8km which is what gives the amazing shadows when close to the terminator. This is also one of the few features that looks great when viewed when it’s a long way from the terminator and you can still get quite good pictures. The peaks in the middle of the crater are about 1.2km high and are separated by valleys. What is also apparent around this crater are the rays which extend almost 800km from the impact site, they aren’t as straight or have the nice radial pattern as the Tycho rays though. Around the crater are also a whole bunch of smaller ones that were created from ejecta of the original impact. Copernicus is the crater with a little bit for everyone to enjoy observing.

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Copernicus Crater from the LRO (Credit: NASA)

You can actually really enjoy all of these features wth a pair of binoculars so no need to go out and spend a lot of money just yet. For those wth more powerful equipment, you’ll get to see the real beauty of a lot of these features. The view won’t be anywhere near as crisp as those depicted here as they are from the Lunar Reconnaissance Orbiter. Now you can eagerly await the Moon rather than lament it’s light pollution qualities and think of the time when Plato City or Sinus Iridium Megalopolis will shine their habitat lights back onto Earth.