The Sun (Science Matters)

studying the Sun The star that is nearest to Earth shines down on people every day. This star is the Sun. It is the brightest object visible from Earth. The Sun provides Earth with light and heat. There would not be life on Earth without the Sun's energy. In ancient times, people believed that the Sun was a life-giving force. They knew that this glowing object in the sky gave life to plants, animals, and humans.

The Sun looks like a solid ball from Earth. Scientists have leamed that the Sun actually has several layers.

Sun Facts Did you know that the Sun is about 4.5 billion years old? Read on to learn more fascinating facts about the Sun.

The Sun is 870,000 miles (1.4 million km) in diameter.

• The Sun is a type of star called a yellow dwarf.

• The Sun's gravity is 28 times stronger than Earth's.

Nine planets, including Earth, orbit the Sun,

Earth could fit inside the Sun about 1 million times.

Sunlight takes 8 minutes to reach Earth.

The Sun in the Past The Sun has been called many names in the past. The Norse people called the Sun Sol. They believed that the Sun was a goddess. Sol was chased across the sky every day by a wolf named Skoll. The Egyptians called their Sun god Ra, He was an important god to the Egyptians. Ra traveled through the sky every day in a sailing craft. In early times, many people believed that the Sun was a powerful god.

Ra was usually shown with a human body and a falcon head.

Icarus Falls Many people prayed to the Sun in ancient times. They admired the Sun because it gave life. People also feared the Sun for its extreme heat. The Sun is an important part of the story of Icarus.

A Greek myth tells about a boy named Icarus. Icarus flew in the sky using wings that his father had made for him.The wings were made of feathers and were held together with wax. The boy's ^^ father warned him not to fly too close to the Sun. Icarus did not listen to the warning.The Sun's heat melted the wax, and the wings came apart. Icarus fell to his death.

What is the Sun? The Sun is a star. This means that it is a large ball of glowing gas. Hydrogen is the main gas that forms the Sun. The temperature of the Sun's surface is about 10,000° Fahrenheit (5,538"C). It is even hotter above and below the surface of the Sun. The Sun's core is about 27 million" Fahrenheit (15 million°C).

The Sun is a second-generation star.This means that it was formed out of dying stars.

The Sun's Corona The corona is the area just above the surface of the Sun. It is much hotter than the Sun's surface. Scientists are still trying to find out why the Sun's corona is so hot.

The Sun's corona can be seen from Earth during a solar eclipse. A solar eclipse occurs when the Moon passes in front ofthe Sun.The Sun, the Moon, and Earth are in a straight line a few times every year. When this happens, the Moon blocks the Sun from our view.The Sun's corona is most visible during a solar eclipse.

Seasons and the Sun Earth orbits the Sun. It takes 1 full year for Earth to complete a circle around the Sun. Earth spins like a top while it orbits the Sun. The Sun shines on different parts of the Earth throughout the year. North America faces the Sun in summer. This is why summer is warm. North America faces away from the Sun in winter. This is why winter is the coldest season

Earth tilts and spins while it circles the Sun.This creates the four seasons.

A Life of Science Nicolaus Copernicus

Nicolaus Copernicus lived about 500 years ago. People believed that Earth was the center of the universe at that tinne.They thought that the Sun and the planets orbited Earth. Nicolaus Copernicus believed the opposite. He thought that Earth orbited the Sun. He believed that other planets circled the Sun as well. Nicolaus used mathematics and science to support his claims.Today, scientists know that he was right.The Sun is the center of our solar system.

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Solar System Map Match each planet on the left to its orbit in the diagram. This will show you the order of the planets in our solar system.

•

Mercury

•

Venus •

•

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Earth

/

Mars

/

Jupiter

I

Saturn

\ ^^

Uranus Neptune Pluto

^

^

The Sun ¡n Nature All of the world's food requires the Sun's energy to grow. Green plants use the light energy from the Sun to make their food. This process is called photosynthesis. Animals and humans eat plants. They take in the Sun's energy that is stored inside.

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The Sun's energy also creates weather by heating the , air. Earth would not have wind or rain without the Sun.

Plants need the Sun's energy to grow.

Guiding Light Humans have used the Sun as a guide for thousands of years. Did you know that some animals also use the Sun asa guide?

Monarch butterflies fly to warm areas before the winter season.They use the Sun as a compass. The location ofthe Sun in the sky directs their migration. Monarch butterflies migrate more than 2,000 miles (3,219 km) every winter.

Sun Science The Sun is an important object of scientific study. Scientists are always trying to learn more about the closest star to Earth. They use satellites, space shuttles, and telescopes to study the Sun. Scientists can also study the Sun from the International Space Station. This space station orbits the Earth.

The SPARTAN-201 was created to gather information about the Sun's corona.

Planet Distances Nine planets orbit the Sun in our solar system. Some are close to the Sun, and others are far away.

PLANETS

DISTANCE FROM THE SUN

MERCURY

36 million miles (58 million km)

VENUS

67 million miles (108 million km)

EARTH

93 million miles (150 million km)

MARS

142 million miles (229 million km)

JUPITER

484 million miles (779 million km)

SATURN

891 million miles (1,434 million km)

URANUS

1,785 million miles (2,873 million km)

NEPTUNE

2,793 million miles (4,495 million km) 3,647 million miles (5,708 million km)

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Humans and the Sun Some people think that having a suntan looks healthy. A suntan is actually damaged skin. Damage to the skin is caused by too much sunlight. Sun damage can lead to skin cancer. It also causes wrinkles. This can make people appear older than they really are. Wearing sunscreen protects the skin from the Sun's rays.

Sunscreen wears off in the water. Be sure to apply sunscreen after swimming.

Solar Energy The Sun gives off energy in the form of light. This is called solar energy.

People have invented a new way to use the Sun's energy. Sunlight is turned into electricity by solar panels. Solar panels collect and use the Sun's energy. Solar energy is an important energy source.This is because supplies of other energy sources, such as oil and gas, are disappearing. Solar energy may one day become Earth's main energy source. Large solar panels and curved mirrors are used to collect the Sun's energy.

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Surfing Our Solar System How can I find more information about space? • Libraries have many interesting books about space. • Science centers are great places to learn about space. •The Internet offers some great Web sites dedicated to space. Where can I find a good reference Web site to learn more about space? Encarta Homepage www.encarta.com • Type any space-related term into the search engine. Some terms to try include "asteroid" and "galaxy." How can I find out more about space, rockets, and astronauts? NASA Kids http://kids.msfc.nasa.gov • This Web site offers puzzles and games, along with the latest news on NASA's research.

Science in Action Egg, Sunnyside Up! You can use the Sun's energy to cook food on a hot, sunny day. Make an outdoor stove by placing some shiny foil on the ground. Crack a raw egg onto the foil. Watch as the clear part of the egg begins to turn white.This means that the egg is cooking. Caution: Do not eat the egg because it may not be completely cooked. It is dangerous to eat uncooked or partly cooked eggs. Sun Cards Do you want to see the effect of the Sun's rays on materials? Take sonne construction paper and a few small objects, such as keys and little toys. Cut the construction paper into card shapes that are about the size of your hand. Lay the cards outside on a sunny day. Place the small objects on top of them. Leave the cards and objects outside all day. By the end of the day, the Sun's rays will have faded your cards.This leaves a design on your cards.

What Have You Learned? What is the of the star

What kind of star is the Sun?

closest to Earth?

What did the Egyptians call the Sun god?

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What causes Earth's weather?

If you could travel to the Sun, would you be able to walk on its surface?

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How long does it take Earth to complete one orbit around the Sun?

How do monarch butterflies migrate to warm areas?

's sunlight good for

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What invention allows humans to use the Sun's energy?

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Would you like to visit the International Space Station?

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Wördstoknöw compass: an instrument that shows directions

myth: a story or legend, often about gods or heroes

core: center of something

orbit: the circular path a planet makes around an object in the sky, such as the Sun

diameter: the measurement of a straight line passing through the center of a circle

satellites: orbiting spacecraft

gravity: force that pulls things toward the center

telescopes: instruments that make distant objects appear closer

hydrogen: a light, clear gas that burns easily

yellow dwarf: a star that gives off a yellow glow

migration: travels from one place to another

Index Copernicus, Nicolaus 11 core 8 corona 9,16 Earth 4,5,8,9,10,11, 13,14,16,17 energy 4,14,19,21

International Space Station 16

seasons 10 Sol 6 solar eclipse 9

monarch butterflies 15,23

telescopes 16

North America 10

yellow dwarf 5

orbits 5,10,11,16,17 gravity 5 Ra 6 hydrogen 8 JA