It’s got holes in it!

What do you see when you look at the Moon?

If you live with high levels of light pollution from streetlamps or commercial buildings or an annoying floodlight on a neighbour’s house – all of which are significant problems – then the Moon may be one of the few celestial object you can bank on seeing in the night sky. It’s a reliable presence whether we’re in the middle of town or the depths of the countryside. So, what do you see? A bright disk/crescent with some darker patches; perhaps you also notice a few curved lines?

A couple of weeks before Christmas I had the opportunity of showing more than fifty 9-10 year-olds* and their teachers what the (daytime) Moon looks like through a telescope. A handful told me that they had an older sibling or a parent with a telescope, but for most this was evidently a wholly new experience. In a brief introduction inside their warm school building – it was -2ºC outside – I’d suggested two or three things they might look out for: the lava fields/‘seas’ for sure, but also the distinct curve of the lunar Alps and the nearby crater named after Archimedes. For the majority, the first-timers, they all – and I do mean ALL – seemed to find the experience quite special, almost magical in some cases. Some of their reactions were priceless; three or four of them looked, looked again and then told me that the Moon had holes in it, which was a novel way to describe lava seas and deep craters. One or two uttered something I pretended not to hear, but which made me chuckle inside nevertheless.

Although not taken on the day, or even through the same telescope, this is similar to the view everyone would have had of the Moon during our morning session. I’ve added a few labels, including the Apollo 11 landing site, to make it easier to orient ourselves. For a good quality lunar map I have installed ‘LunarMapHD’ on my phone.

In order to avoid having anyone get too cold – anyone other than me and the member of staff with me that is – there were only eight pupils out there at any one time and they were all wrapped up against the chill. Finally, the staff members also had a chance to take a peek before we bundled back inside for an extended and wonderfully lively Q&A session. As with my visit to the school towards the end of the last academic year, when the previous Year 5 classes had the chance safely to observe sunspots (see here), the questions posed were far-ranging and challenging. More than once I had to say that I didn’t have an answer, but on the whole we were able to cover a lot of ground to everyone’s satisfaction. Some of the questions opened up important generic topics like the nature of science and the need to make decisions based on the best available evidence, whereas others were a lot more specific. In that latter camp there were many which arose from what they’d observed: what are the darker areas and why are there fewer craters within them; why are there some areas that seem particularly bright; how did the Moon form …? (Answers below.) We also explored the lifetime of stars, exoplanets and a question that arose at least three times in one guise or another: why are the planets different colours?

This is a composite image of a few of the morning's lunar observers; such a great bunch. (The images are included with appropriate consent and permissions having been obtained.)

All-in-all I was deeply impressed by the degree of their engagement and by their perceptive and well-phrased questions. I suspect that there are several budding scientists in their number, and I wish them well.
Happy lunar observing everyone 😀.

____________________________________

* I absolutely must mention the warm and enthusiastic welcome I got at The Churchill School which included the help of two class members, Teddy-Rose and Lewis (see image below, reproduced with appropriate permissions): with great care they helped me to ferry my equipment from the car to the playground we’d be using. The staff were amazing, and filled me with confidence that these children were in the best of hands: thank you for the invitation Mrs. Newport (yes, well spotted: the best of daughters-in-law) and thank you to your colleagues: Mr. Moore, who braved the cold with me in order to take photographs, Mrs. Lejeune and Mrs. Coleman. Also, many thanks to the school’s Deputy Head, Andrew, who made me a mug of tea 😊.

A few brief illustrated responses to the questions posed above:
The darker areas are solidified lava flows following a past impact. If something large enough collided with the Moon there’d be sufficient energy released to melt some of the lunar surface – to turn it into lava – which then cools and solidifies to leave a smooth patch. This violent process will of course obliterate all traces of former craters caused by smaller impact events, which is why there are fewer craters to be seen. It also means that any craters that do sit within a lava sea were caused relatively recently in geological terms.

The Moon formed from the debris of a gigantic collision between an original Earth and another body about the size of present-day Mars which took place in the early stages of the solar system. This is almost certainly easier to comprehend in pictures than through words alone, so take a look at one or both of these video clips: BBC, NASA.

There’s no left or right, up or down in space so I’ll not apologise for the fact that this image of mine is flipped horizontally compared to the earlier one. The point of including it is to show that even the Moon has colour. We don’t see it because it’s muted and because it’s so bright overall that the colours are washed out – technically, it has a high albedo which simply means that it reflects a high percentage of the sunlight falling on it. However, in a digital image it’s possible to increase the colour saturation whilst holding back the brightness to show that the Moon’s surface geology does indeed imbue colour. As with all the planets, they appear as one colour or another by virtue of what’s on the outer surface. Thus Venus appears white because it’s totally covered with reflective clouds, whereas Mars has a reddish hue because there’s a lot of rust (oxidised iron compounds) on its surface; Uranus and Neptune appear blue-green and blue because of the hydrocarbon gasses which make up their respective atmospheres. (The Sun and other stars are different simply because they generate their own light; their varying colours from red to blue arise from their surface temperatures.)

There are several particularly bright areas which, if one looks closely, often seem to be associated with bright ‘rays’ extending from a crater or cluster of craters. It turns out that there is quite a lot of glass on the Moon’s surface – made when material was melted in a collision with, perhaps, a small asteroid – and it’s this material that reflects so much sunlight. Most domestic glass on Earth, like window glass for example, is made from a mixture of various chemicals with silica (sand!) but we can make a glassy material from all sorts of source materials if the heating and cooling rates are right. There are some terrestrial examples of this shown in the image above. The material shown on the left is a naturally-occurring glass called tektite and the yellowy material next to it is often referred to as ‘desert glass’; both are relatively pure samples of silica glass made when a meteorite plummeted into desert sand. The central image is of obsidian glass, which is formed in a volcano. The sample on the right is a glassy material which formed as a waste product in a commercial furnace dating to the Middle Ages.

We all know that shadows are longer when the Sun is low in the sky; the same holds true on the Moon, so the further away we are from a full Moon – when the Moon is face-on to the Sun – the easier it will be to pick out mountain ranges, valleys and craters. Speaking of mountains, this image of the Sun, taken alongside one of my grandsons during the partial solar eclipse which occurred on October 25th 2022, shows that the Moon has a slightly ‘crinkly’ edge because of its many mountains. (You’ll also be able to spot the sunspot clusters that were visible at the time.) I hope it goes without saying that these images are not to scale.