ASTR-201 Lessons

ASTR 2.1: Introduction to the Moon and Year Two

Year Expectations

Good morning, students, and welcome to another year of Astronomy. I enjoyed teaching First Year Astronomy last term, and I am glad to see so many of you back in class after the term break.

The class expectations from last year have not changed: show up to class, take notes, do your own work, and ask for help if needed. You will also be happy to know that you will not have to buy any new materials for class this year; there is no textbook again, and you can use your von Rheticus model telescope from last year. As an important note, please bring said telescope to class every lesson from next week onwards.

There is, however, one major change to the class expectations: this term, there will be two required Astronomy essays. One of the required essays will be this week’s, and the other will appear later in the year. If you are nervous about these essays, do not be; think of them as another way to express your thoughts and show what you know. You also still have access to last year’s optional essays; feel free to “warm up” on those before attempting the required ones, if desired.  The distribution of marks will be the same as in Year One: 75% for content and 25% for presentation, consisting of 10% for meeting the minimum word count as is indicated in the prompt, 10% for spelling and grammar (unless you indicate NES or LD at the beginning of your essay), and 5% for not including any identifying information (such as your name and house).

Preview of Year Two

This year, we will be learning more about some very exciting topics relating to the Moon.  We will learn about how tides, phases, and eclipses work and will discuss the magic behind a syzygy, which is an alignment of three astronomical bodies.  A good portion of the year will be focused on studying beasts and plants that are affected by the Moon’s cycles as well as other effects of lunar magic, and believe me, there are quite a few!  We will also discuss some of the moons of the other planets of the solar system, and finally, some folk tales and scientific theories about the origin of the Moon.

Below is a more organised  list of the topics to be discussed in each lesson this year.

Basics of the Moon

This year we will be focusing on learning more about the Moon.  Even though the Moon’s “light” is actually light reflected from the Sun, it still affects us on Earth in a unique way. For those who grew up in magical households, for example, you have probably heard warnings about werewolves turning into their beast form under the influence of a full Moon.  For those who grew up in Muggle households, perhaps you have heard stories - inaccurate as they may be - about witches in pointy hats riding a broomstick across the backdrop of the Moon.  As we all know, although witches sometimes do wear a pointy hat and ride a broom, as do wizards, they can do so at any time of day, with or without the Moon in the sky, but I digress.

Before discussing the Moon’s magical properties, though, we have to get through some mundane information.  While it may not be as enthralling, it is just as important!  Starting with the Moon’s diameter, it is about 3474 kilometres, which is about 0.28 times that of Earth. I hope it comes as no surprise that it’s smaller than our planet!  Continuing with the comparisons, its mean density is 0.61 times that of Earth and its mass is 0.012 times that of our planet.  To put it in a bit more perspective, Earth is over 80 times more massive than the Moon! One better-known difference is its gravity - specifically its surface gravity - which is about 1/6 that of Earth’s, making it easier for the astronauts who landed on the Moon from 1969 to 1972 to move around despite having to wear a heavy space suit.  If you want to learn more about the Moon’s physical characteristics, you can find more information here. 

The Moon, like Earth and all the other planets, is spherical. Of course, it’s not a perfect sphere. Like some of the planets, the Moon has places of high elevation and places of low elevation as well as flat land and areas with more jagged profiles, like mountains.  The portions of the Moon's surface that appear light to us are areas of higher elevation – also known as the “highlands” – and the dark portions are flat, plain-like areas created by cooled lava from ancient volcanoes. These dark, flat areas are called “mare” or “seas,” based on a previous incorrect assumption that they were lunar seas.  As a tie-in to your studies from First Year, the light areas have a higher albedo than the dark areas, and, as we learned, the higher the albedo of a surface, the more magic it reflects.  In addition to these naturally-occurring features, the Moon is also covered with craters, caused by impacts with smaller objects like asteroids, comets, and meteoroids.  

Another interesting, and important, tidbit about the Moon’s physical appearance is that the same side of the Moon always faces Earth.  The side that faces us is called the “near side” and the side that faces away is called, you guessed it, the “far side.”  Yes, good observation, the Moon does appear to wobble a bit, so an observer on Earth who looks at it often enough over the course of a month can actually see about 59% of it.  I was about to mention that fact, but you beat me to it.  Five points to … uh, what house are you in?   Anyway, I’ll explain the reasons for this particular phenomenon in the next lesson!  

For now, though, let’s talk some more about the near and far sides of the Moon. You may be wondering how we know anything about the far side if we’ve never seen it before. While we haven’t viewed it from the ground, it has actually been seen both by satellites orbiting the Moon and by a space probe!  The pictures on the screen in front of you, which were taken from NASA's Lunar Reconnaissance Orbiter, show the near side and the far side of the Moon, respectively.  In addition, as I mentioned last year, the Chinese landed a spacecraft on the far side in 2019, which has further added to our knowledge.  If you want to learn more about the Chinese spacecraft and what it discovered, you can find more information here. 

The near side of the Moon

Source: here

The far side of the Moon

Source: here

Let It Shine

Now, as stated, the Moon does not generate any light itself; it appears to shine in the night sky because it reflects light from the Sun. Interestingly, have you ever noticed that even when the Moon is in its crescent phase, the darker area still looks to be slightly lit up?  In an even bigger twist, that glow is actually earthshine, or light from the Sun reflected off Earth to the Moon.  See the image below.

Earthshine

Source: here

Either way, all moonlight was originally sunlight. That being said, we as magical people know instinctively that moonlight does not have the same effects as sunlight. We can clearly see this through the example of werewolves. Werewolves maintain their human form during the day and most nights. While they are in their human form, you can’t detect their condition just by looking at them. However, on the night of the full Moon, they turn into their wolflike form, and unless they take Wolfsbane Potion, they will respond with the violence and behaviours you would expect of giant wolves (more about them in Lesson Five). These observations seem to suggest that even though moonlight is reflected sunlight, something about being reflected off of the Moon changes the light's magical properties, which should come as no surprise to you since, as you learned last year, the planets do the same thing.  The far side of the Moon looks different from the near side, so the magic it reflects could very well be different too.  Fortunately, since the Moon keeps (almost) the same side facing the Earth at all times, the magic reflected from the Moon to the Earth is predictable and consistent.

Concluding remarks

There will be a ten-question quiz and a mandatory essay.  Class dismissed.

The original lesson was written by Professor Turing

Part of this lesson was written by Professor Plumb