Chapter: 15. The Solar System
15 The Solar System
Introduction to Heavenly Bodies
When you look up at the sky, whether it’s day or night, you see many amazing things! During the day, you see the bright Sun, and at night, you see the Moon and countless twinkling stars. These natural objects in the sky are called heavenly bodies.
Some important terms to know when we talk about space are:
The Sun: The star closest to Earth, providing heat and light. The Moon: Earth’s natural satellite. Solar system: The Sun and its family of planets, satellites, rocks, dust, and gases. Planets: Heavenly bodies that travel around the Sun in a fixed path. Heavenly bodies: Natural objects found in space, like the Sun, Moon, and stars. The Earth: Our home planet, a living planet. Stars: Heavenly bodies that have their own light and heat, made of hot gases. Satellites: Objects that go around a planet.
The Solar System
Our universe is vast and full of many heavenly bodies. Many of these bodies move around a central star. The Sun, along with its entire family of eight planets, their satellites (or moons), and also pieces of rocks, dust, and gases, all form what we call the solar system.
The Sun
The Sun is a very important part of our solar system.
It is a star, and it’s the closest star to our Earth. The Sun is like a giant ball of very hot, burning gases. All the planets in our solar system travel around the Sun. We can see the Sun clearly during the day because it is so close to us, unlike other stars which appear only at night and look much smaller because they are farther away. The Sun provides us with essential heat and light. Without the Sun’s heat and light, Earth would be extremely dark and cold, and life as we know it would not be possible here. Factpedia: The Pole Star
A Pole Star or North Star is the brightest star in the sky in the northern part of the world. By finding the Pole Star, you can easily figure out the other directions (North, South, East, West).
Planets
A planet is a heavenly body that travels around the Sun. Each planet follows a specific, fixed path as it goes around the Sun. This path is called an orbit.
The time it takes for a planet to complete one full orbit around the Sun is how long a “year” is on that planet. For example, Earth takes about 365 days (a little over a quarter) to complete one orbit, which is why a year on Earth is 365 days long.
Our solar system has eight planets. They are named in order of their closeness to the Sun:
Amazing Facts About Planets
Let’s learn some fascinating facts about each of the eight planets in our solar system:
It is the smallest planet. It is the first planet from the Sun. It takes only 88 days to orbit the Sun. It is the brightest and hottest planet in the solar system. It is the planet closest to Earth. It is a planet with no natural satellite (no moon). Our home planet, also known as a living planet because it supports life. It is called the blue planet because it looks blue from space due to its oceans. It takes $365 \frac{1}{4}$ days to go around the Sun. It is the fourth planet from the Sun and the second-smallest planet. It is known as the red planet because its surface is covered with red dust. Green Earth Fact: Like Earth, Mars also has mountains, valleys, and volcanoes. Olympus Mons, the solar system’s largest volcano on Mars, is three times taller than Mount Everest! It is the largest planet in the solar system. It is mainly made up of gases. It has the maximum number of moons (satellites). It is the second largest planet in the solar system. It is famous for being surrounded by many beautiful rings made of ice crystals. This planet is unique because it spins around the Sun lying on its sides. It has many dark rings around it. It also has many satellites. It is the farthest planet from the Sun. Because it’s so far, it receives very little heat from the Sun, making it extremely cold and giving it the worst stormy weather. From Earth, Neptune can only be seen with a telescope. Mnemonics: Remembering Planet Order
An easy way to remember the order of the planets from the Sun (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune) is to use a mnemonic device, like this sentence:
My - Mercury
Very - Venus
Enthusiastic - Earth
Mother - Mars
Just - Jupiter
Served - Saturn
Us - Uranus
Nachos - Neptune
Satellites
A satellite is an object that travels around a planet. There are two main types of satellites:
Natural satellites: These are objects that occur naturally in space, like moons. All planets in our solar system, except for Mercury and Venus, have natural satellites. Artificial satellites: These are man-made objects that are sent into space to orbit planets. Artificial satellites are very useful! They provide us with a lot of information about other planets and help us predict the weather. They also make modern communication possible, allowing us to use television, telephones, and radio signals.
The Moon
The Moon is a very familiar heavenly body to us, as it is the natural satellite of the Earth.
The Moon does not have its own light. We can see it from Earth because it reflects light from the Sun, making it appear to shine. There is no air or water on the Moon. Because there’s no air or water, nothing can live or grow on the Moon. Even though the Moon is much smaller than the Earth, it looks quite big to us because it is relatively closer to us than other heavenly bodies. If you look closely at the Moon’s surface, you might notice large pits or bowl-shaped depressions. These are called craters.
The Stars
When we gaze at the sky at night, we see countless stars twinkling. Stars are fascinating heavenly bodies with unique characteristics:
Stars have their own light and heat. They produce it themselves! They are made of very hot gases. Many stars are actually much bigger than our Sun. However, they look tiny to us because they are incredibly far away. A vast group of thousands, or even millions, of stars forms a galaxy. There are many, many galaxies throughout the universe. Our solar system, including Earth, belongs to a galaxy called the Milky Way galaxy. When we look at the night sky, sometimes we can see groups of stars that seem to form a recognizable pattern or shape. These patterns are called constellations.
Some famous constellations you might hear about include:
Great Bear (also known as Ursa Major) Chapter Summary
Here’s a quick recap of what we’ve learned in this chapter:
The Sun, the Moon, and the stars are all called heavenly bodies. The solar system includes the Sun, the eight planets, their satellites, and also rocks, gases, and dust. The Sun is a giant ball of hot burning gases that provides us with heat and light. A planet is a heavenly body that travels around the Sun in a fixed path called an orbit. A satellite is an object that goes around a planet. Stars have their own heat and light and are made of hot gases. When stars form patterns in the sky, they are called constellations.
Self Study
