Sun
The Sun is very important to you. You play in sunshine. You see in daylight. The Sun keeps you warm. Even ancient people knew the Sun was very important. They thought the Sun was a god. The ancient Greeks thought the Sun god drove a chariot across the sky every day. The ancient Egyptians thought the Sun god sailed a boat across the sky. Today we know that the Sun is a star. The Sun is the star at the center of our solar system. Earth and all the other planets orbit, or go around, the Sun. The Sun is very important to all life on Earth.
THE SUN IS A STAR
The Sun is a star—a ball of hot, glowing gas. It does not have any solid parts. It is made up mostly of hydrogen gas and helium gas. The Sun is huge compared with Earth. If the Sun were hollow, a million Earths could fit inside it. The Sun looks small only because it is far away. The average distance from Earth to the Sun is 93 million miles (150 million kilometers). You would have to go around the world more than 3,700 times in order to travel that far on Earth.
The force of Earth’s gravity holds you on the ground. The Sun’s gravity holds Earth and the other planets in their orbits. It holds asteroids, comets, and dust in orbit.
The Sun is one of about 400 billion stars in the Milky Way Galaxy. A galaxy is a large group of stars. The Sun and all the other stars orbit the center of the Milky Way.
ENERGY FROM THE SUN
Almost all the energy on Earth comes from the Sun. Heat from the Sun makes Earth warm enough for life. Plants use the Sun’s energy to live and grow. Plants give off a gas called oxygen. Animals eat the plants and breathe the oxygen. Animals need plants in order to live, and plants need the Sun.
You use plants to make heat and energy. You can burn wood from trees. You can burn fossil fuels called coal, gas, and oil. Fossil fuels formed deep underground from plants and animals that died millions of years ago.
The Sun’s energy can also do harm. Too much sunlight can burn your skin, causing sunburn. Harmful rays from the Sun can also cause a disease called skin cancer. Looking right at the Sun can harm your eyes. You need to be careful of the Sun.
THE CORE OF THE SUN
The center of the Sun is called the core. The core is extremely hot. The heat sends tiny bits of matter called atoms crashing into each other. The crashing atoms set off atomic or nuclear reactions. All the energy of the Sun comes from these nuclear reactions in its core. It takes a long time for the energy from the core to reach the surface of the Sun—about 170,000 years!
THE SURFACE OF THE SUN
The photosphere is the outer part of the Sun that we can see. Like the rest of the Sun, the photosphere is made of hot hydrogen and helium gas. Heat and light from the photosphere reach Earth. The temperature of the photosphere is about 9950° Fahrenheit (about 5500° Celsius).
Fountains of red-hot gas shoot up thousands of miles from the photosphere into the Sun’s atmosphere. Cooler dark spots called sunspots form on the photosphere.
Far above the photosphere is the corona. The corona is the top layer of the Sun’s atmosphere. The corona is so faint that the only time you can see it is when the light from the rest of the Sun is blocked. Astronomers use discs to block the light so they can study the corona. The temperature of the corona goes up to 4 million degrees Fahrenheit (2 million degrees Celsius). The corona trails off into space. Gases that blow off the corona are called the solar wind. The solar wind reaches far beyond Earth.
THE SUN IS A MAGNET
The Sun is a huge magnet. The magnetism of the Sun causes strange things to happen. Bright explosions called solar flares flash in the corona. The flares send gases looping out into space. Sometimes there are huge explosions in the corona that send billions of tons of material into space. The flares and explosions can cause magnetic storms on Earth. These storms cause problems for satellites and cell phones.
HOW DID THE SUN FORM?
Astronomers believe our solar system formed about 4.6 billion years ago from a swirling cloud of dust and gas. The Sun formed first at the center of the cloud. Then the planets formed from dust and gas going around the Sun.
Someday the Sun will burn out. It will use up all the fuel in its core. You don’t need to worry. Astronomers say that the fuel will last several billion more years.
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