The Sun and the Earth
Thank goodness for the sun! Life couldn’t exist on Earth without it. There are lots of reasons why. For one thing, the sun’s heat keeps Earth from being an unlivable ball of ice.
What exactly is the sun? What are some of the ways our world depends on it? And how does it sustain life?
Star of the Show
Our solar system just has one sun. Some solar systems have two or more! But one sun is all we need.
Not only is our sun the star of the show here on Earth, it’s actually a real star. Although our sun may be special to us, it’s just one of millions and millions of stars in the universe. Just look up at the sky on a clear, dark night and you will see plenty. Stars come in different types. Ours is a type called a yellow dwarf star. Even though it’s closest star to Earth, it’s still 94.43 million miles away from us.
Our sun formed from space dust 4.6 billion years ago. That same cosmic dust formed all the planets in our solar system, including Earth, but most of it went into making the sun. In fact, the sun contains more than 99% of all the matter in our solar system. Even though it’s not the biggest type of star, our sun is big enough to fit more than one million planets the size of earth inside it.
The sun is made almost completely of just two elements: hydrogen and helium. It is very hot: over 10,000° Fahrenheit. That heat is generated by a reaction between hydrogen and helium called a fusion reaction. That is far too hot for an astronaut, or even a spaceship, to get close to. No wonder NASA isn’t planning any missions to the sun anytime soon.
The reason for our seasons
Like all planets, Earth orbits its sun. It takes 365.25 days for Earth to make one complete trip around our sun. That’s what we call a year, of course. Every four years, we add an extra day, called Leap Day, to catch up with the extra quarter days.
At the same time that Earth is circling the sun, it is also rotating on its axis. The axis is a line from the north to the south pole, through the center of the earth. Each rotation is a day. So when you watch the sun “rise,” it’s really you that is moving, riding along as Earth spins around on its daily rotation.
If a year is one orbit, and a day is one rotation on an axis, what is a season? Seasons occur because our planet is tilted on its axis. That tilt creates seasons. When the northern hemisphere is tilted away from the sun, it’s winter in the North America and other northern continents. When the southern hemisphere is tilted away from the sun, it is winter in South America and other continents in the southern hemisphere.
Bringing life to Earth
The sun’s heat is the only reason we exist here on Earth. It warms our planet to just the right temperature for life.
The sun gives us more than warmth. Plants—the basis of all our food —need the sun’s energy to create their own food. Without the sun, we wouldn’t have flowers, apples, broccoli, wheat, sugar, or any other food. Plants are more than food: without them, our atmosphere also wouldn’t have the oxygen that we need to breathe. Besides food and warmth, our bodies need sunlight, too. It provides us with Vitamin D, an essential ingredient for healthy bodies.
So, the next time you are enjoying a meal, savoring a warm afternoon, or just feeling grateful for the life all around you, don’t forget to thank your lucky star: our sun.
Written by Laura McCamy
Edited by Beth Geiger, MS Geology
Illustrated by Renee Barthelemy