Blog 1: Moon Monday: That Big Round Thing In The Sky

Blog 1: Moon Monday: That Big Round Thing In The Sky

By Mélissa M Azombo

“Big round thing in the sky! You couldn’t keep away, could you?” – The Doctor, Doctor Who, Series 6, The Impossible Astronaut. The Doctor was of course right. The Moon even became the main target of the space race. But was it really worth it? What’s so fascinating about the moon that it’s worth investigating?

Well, first of all, of course it was and there are many, many fascinating things about the Earth’s moon, which make it worth investigating.  However, for the purpose of the limited dimension that is time for humans, I shall keep that to 4 points.

Craters: Inevitably, the most visible features of the moon are its craters. They are noticeable with the naked eye and can be seen very clearly with a telescope. Craters such as Copernicus, Tycho and Picard give great reason to want to enquire about and study the Moon further. This is because they give us an insight into the geology – or moonology – of the Moon. A cratered surface indicates an old surface, which has encountered impacts from other bodies, such as meteors. So is a non-cratered surface a brand new one? Not necessarily, as this shows evidence of resurfacing. The planetary body has had time to “heal its wounds”, if you wish, making the ex-cratered surface smoother over time.

Tides: Furthermore, it is a generally well-known fact that the Moon is responsible, in conjunction with the Sun for our tides, due to its gravitational effect. However, the Sun only has 45% the power of the Moon when it comes to tides. Although the Sun is much more massive, with a mass of 2.0X10³⁰ kg (That’s 20000000000000000000000000000 kg), in comparison to the moon with a mass of 7.3 X10²² kg, the Sun is also much further away from Earth than the Moon’s 384 000 km distance, at a distance of 149597871 km, a distance known to astronomers as 1 astronomical unit (1 au). As the Inverse-Square Law dominates (More on that on Wednesday), the fact that the Sun is further away means it has less of an impact on Earth’s tides than the Moon does.

So, how do tides occur? Firstly, it is important to distinguish between the 2 types of tides which exist. There are Neap tides and Spring tides. Neap tides occur when the Moon is at its waxing or waning phase, so the Sun, Earth & Moon are not aligned. On the other hand, Spring tides occur when the Sun, Moon and Earth are aligned, so the Moon is at its Full or New phase. In either case, tides are caused by the Moon’s gravitational pull, causing the waves to rise up and fall. As a result of the Earth rotating over 24 hours a day, 2 tides will be experienced per day, although some places do only experience 1. This means, if the Moon was far away enough, it wouldn’t cause the Earth to have any tides at all.

Position In The Sky: Once upon a time, the Moon was incredibly close to the Earth. Therefore, the Moon appeared much larger in the sky and tides would have been much greater. On top of that, there is one particular factor, which makes studying the Moon at this point in time incredibly significant. On 20 March 2015, some of the Northern Hemisphere witnessed a total solar eclipse – a phenomenon which would not have applied in the past. Had the Moon and the Sun been aligned, the Moon would have covered the Sun so that it would have completely blocked it (imagine a big crisp in front of a small crisp), due to their sizes and distances. Today, the Moon is at a distance that means in the event of a solar eclipse, it exactly covers the Sun, allowing corona filaments to be visible just over it, from behind. This, I think, is why we are entitled to be more inquisitive about the Moon now, than ever before!

So, there are tons of reasons we should keep studying the Moon, whether that is to attempt to find life on it or to delve further into the Universe’s past. I could go on forever, but I am sure you don’t have that long. No, honestly. I’m sure. I’m afraid you’ve only got about 5 billion years. Want to know why? Find out in my next article….