Chapter 5: Galactic Lectures on the Solar System
Galactic: “Our Solar System is in an outer spiral arm of the Milky Way Galaxy. It consists of the sun and everything that orbits it: eight planets, moons (satellites) asteroids, comets, meteorites, dwarf planes, and smaller debris. It takes 250 million years for our Solar System to orbit the Milky Way. It also takes 250 million years for the Milky Way to complete a rotation.”
“Asteroids are minor planets. There are millions of them. Ceres a dwarf planet (590 miles in diameter) resides in the Asteroid Belt.”
Galactic: “What’s the definition of a planet?”
Student: “It’s an object that orbits the sun.”
Galactic: “That’s partially correct. The definition is:
It must orbit a star.
It must be big enough to have enough gravity to force it into a spherical shape.
It must be big enough to clear away other objects of similar size near its orbit around the sun.
“The word ‘planet’ means wanderer in Greek. There are eight planets: Mercury, Venus, Earth and Mars are the rocky planets. They’re made mostly or iron and rock. Earth has one natural satellite, the moon, and Mars has two. Earth is the largest of the rocky planets.”
“The outer planets are Jupiter, Saturn, Uranus and Neptune and are gas planets, Jupiter being the largest. These planets have dozens of moons ranging from rocky to icy to volcanic (Jupiter’s Io). They’re composed of hydrogen and helium and have no solid surface; some have rocky cores. Rings of dust, rock and ice encircle these giants with Saturn’s being the most famous.”
Student: “How did the rings form?”
Galactic: “Some were formed when the moons broke up due to the immense gravity of Saturn or when the moons collided.”
Another Student: “This is too weird to be true. What’s the purpose of all of this?”
Galactic: “That’s an excellent question. Your assignment is to write on the purpose of the universe. The paper should be at least one thousand words.”
Another Student: “Why are there rocky planets and why are there gas planets?”
Galactic: “When the rocky planets were formed there were more rocky debris in the environment and when the gas planets were formed, there were more gases. Okay, let’s continue because I’ve got a lot to cover today.”
“Next we’ll discuss the sun. The sun is 99.8 percent of the solar system’s mass. One million Earths could fit inside the sun.”
“The sun’s influence, the heliosphere or the magnetosphere extends two light-years. The point at which it exerts no influence is called the heliopause. The Oort Cloud extends one light-year and is believed to be a thick bubble of icy debris that surrounds our solar system and is the origin of some of the comets. It continues to the very edge of the solar system.”
Student: “That’s unbelievable.”
Another student: “Cool.”
Galactic: “You have a sense of humor. Most people don’t understand the universe but the curious amongst us want to reduce some of the mystery.”
Another student: “Why?”
Galactic: “You must be kidding. It’s important because you live in the universe and consist of the same elements that planets and stars consist of.”
Another student: “And what’s that?”
Galactic: “Listen up. Your other assignment is to learn what elements your body consists of. That will be due tomorrow. Getting back to the sun, the visible part of the sun is about ten thousand degrees Fahrenheit. The core can reach more than twenty-seven million degrees Fahrenheit.”
Student: “I wouldn’t want to live there.”
Another student: “Stupid, you couldn’t live there.” Everyone laughs including Galactic.
Another student: “Both of you shut up. Let’s hear what Ms Galaxy has to say.”
Galactic: “Thanks. Our sun is a yellow dwarf. Most suns in the Milky Way are red dwarfs; small, cool suns. Our sun and the planets orbit the Milky Way completing a revolution once every two hundred and fifty million years.”
Student: “How old would I be after it completes that orbit?”
Galactic: “I see we have some jokesters. Good! The sun was born 4.6 billion years ago. It’s seventy percent hydrogen and twenty-eight percent helium. The sun’s power is produced by nuclear fusion. Hydrogen is converted to helium. After its nuclear fuel is exhausted, it will swell to a red giant and will collapse to become a white dwarf and then a black dwarf. It doesn’t become a black hole. Only a larger sun will become a supernova and ultimately a black hole,
Student: “What will happen to the earth when the sun swells to a red giant.”
Galactic: “Any answers?”
Another student: “They’ll be no more humans.”
Galactic: “Yes, and all of the rocky planets will be annihilated.”
Another student: “That’s a terrible thing to have to know and worry about. No wonder there are pessimists in this world.”
Another student: “Why? None of us will be here.”
Galactic: “This course doesn’t have time to discuss the Solar System in depth. Next year I’ll be teaching the advanced course, so you can take it then if you’d like.”
“Did you know that I was in space for two years?”
Student: “You look a little spaced out. Just kidding. You look great.”
Galactic: “You all have a gift for gab.”
The class gives their undivided attention as Galactic recounts her experience in space. She doesn’t divulge to her students that she traveled adjacent to the spaceship. They don’t know she’s a superhuman robot. She plans on telling them soon.
Another student: “How far out in the universe did you go?”
Another student: “Far out.”
Galactic: “Another jokester; let’s all clap for his brilliant remark.”
The students clap and laugh. They’re having a lot of fun. Galactic couldn’t help but laugh too,
Another student: “Did that experience change you?”
Galactic: “Every experience changes you, but it had a profound effect on how I view life.”
Same student: “Why did you change?”
Galactic: “Seeing Earth from space is a magnificent sight. You can’t believe that it’s your home. I enjoyed space travel, but I couldn’t wait to get home.”
“Getting back to the subject; now you know a little about a lot. You’re astrophysicists; well not exactly, but you’re on your way.”
Galactic leaves the room smiling. She enjoys her students’ comments. They make light of everything and that makes class enjoyable.