Lesson 7) Moons of the Solar System, Part 1

While entering the classroom, Professor Turing uses his wand to open the drapes so that students will have a clear view of the Full Moon. Then, he magically reveals large images of other Solar System moons, which have been placed all over the classroom.

Good evening, students, and welcome back to Astronomy. There are three weeks left in this course - including this one, of course - and that means that finals are approaching. In the little time that we have left here, I will discuss some very interesting topics that are meant to extend your knowledge about moon-related magic. This week and next week, I will be discussing the moons of other planets of our Solar System. 

Next week, we will also have a very special guest speaker - Janvier Mathieu, a French professor of Magical Astronomy, will talk about the Shepherd Moons of Saturn. She is a personal friend of mine, and she was one of the many astronomers who inspired me to return to school to study magical astronomy.

The last week will not only feature a final but also a relatively light lesson on the Moon’s role in magical culture. The final itself is rather easy - multiple choice questions and short answer questions - but will require you to know information from all lessons of this course. If you study and take your time on the questions, you have a good chance of doing well.




Moons of the Solar System

Moons are natural satellites - essentially astronomical bodies - that orbit a planet. Of the eight planets in the Solar System, the only planet with only one moon is ours - the Earth. As such, we refer to our Moon with a capital “M”, while we refer to satellites of other planets as “moons” with a lowercase “m”. The Earth-Moon relationship also stands out because, in terms of size, the Moon is relatively big compared to the Earth. The word “lunar” is an adjective that refers to “of the Moon” - notice the capital “M”.



Callisto
Image Source: NASA

In the Solar System, it is very common for planets - especially the gas giants (Jupiter, Saturn, Uranus, and Neptune) to have moons. The Inner Planets tend to have fewer moons - Mercury and Venus have no moons; Earth has one moon, and Mars has two moons. The Outer Planets, however, are known for their many moons. 

At the time of this lesson, Jupiter leads the Solar System moon count with a whopping 67 moons. Saturn comes a close second with 62 moons - I will save the discussion of Saturn’s moons for next week’s guest lecture by Professor Mathieu. Although Galileo Galilei was the first to discover that Jupiter has moons while observing the planet in 1610, the majority of the moons of Jupiter have been discovered in the 21st century. This, of course, shows that even today, Astronomy still remains a cutting-edge and rapidly growing field of study. Some of Jupiter’s moons, like Callisto, Europa, and Io, are larger than the Earth’s Moon in terms of mass, but many of the more recently discovered moons are only a few kilometers across. With new techniques and devices developed every day, as well as with more people looking at the skies, there probably are yet  more moons of Jupiter to discover.


Titania
Image Source:
NASA

Uranus and Neptune also have many moons; at the time of this lecture, 27 and 14 respectfully. Uranus, the smallest of the Outer Planets in terms of mass but the second smallest (after Neptune) in terms of diameter, has several moons. Its two largest moons, Titania and Oberon, were discovered in the 18th century. The third and fourth largest moons, Umbriel and Ariel,were discovered in the 19th century; the rest were discovered in the 20th and 21st century. The five largest moons of Uranus are so massive that, had they been in orbit around the Sun like the eight Solar System planets and Pluto, they would have met the criteria to be dwarf planets. As for Neptune’s moons, the largest of the bunch,Triton, is known for its still-functioning geysers that rain liquid nitrogen all over the moon. The orbits of the moons are rather unique; I will discuss this more in a future year.




Extended Example: Martian Moons

We spent several lessons discussing the Moon’s magical impact on the Earth. The Moon’s magical power, though gentle, is powerful enough to have a substantial impact on the magic used on Earth. Even though the Moon itself does not create magic, the Moon affects magic on Earth by reflecting it, and by aligning with other Astronomical bodies. Without the Moon, magic on Earth would be very different.

Let us take what we know about the Moon’s magical effect on the Earth and use it to approximate the effect that another planet’s moons have on their host planet. For this exercise, we will use Mars, the only other Inner Planet to have moons. Although Mars is only 10% the mass and just over half the diameter of the Earth, the example of Mars is easy to analyze because the planet only has two moons - Phobos and Deimos.

     

   
Phobos (left) and Deimos (right), the Two Moons of Mars
Image Source: NASA

Please look at the front of the room to see pictures of Phobos and Deimos, both taken by the Muggles’ Mars Reconnaissance Orbiter. How are these two moons different from the Earth’s moon? The most noticeable difference that can be seen from these pictures is that both Phobos and Deimos are not round; they are shaped like potatoes.

If you look carefully at both moons, you can see something interesting - their relative size. Notice how the image of Phobos is sharper than the image of Deimos? Not only is Phobos much closer to Mars, but it is also much bigger than Deimos. In terms of size, Phobos is almost two times larger than Deimos in diameter and over five times larger in mass. Although Phobos orbits Mars approximately four times in the time that Deimos orbits Mars once, both Phobos and Deimos are tidally locked to Mars just like the Moon is tidally locked to the Earth - the same portion of the moons faces Mars at all parts of the moons’ orbits.

Class today is over. While going over your notes, please think about the Martian situation - specifically how Mars is magically affected by its moons. I will go over the example next week as a partial review for the final. In addition, as we have a well-respected guest speaker from outside the school next week, I expect everyone to be in class on time and ready to learn.

Thank you for your time. Class is dismissed.


The Moon, The Lifebringer

NOTE - This course will soon be undergoing rewrites. Stay tuned!
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