• Our sun is a star located at the center of our Solar System. It is a huge, spinning ball of hot gas and nuclear reactions that lights up the Earth and provides us with heat.

Fun Facts• AGE OF THE SUN

The Sun formed 4.5 billion years ago, as the solar system coalesced from a cloud of gas and dust.

Our sun is a medium-sized yellow star that is 93,026,724 miles from the Earth.

• The Earth is closest to the Sun (this is called perihelion) around January 2 each year (91.4 million miles = 147.1 million km); it is farthest away from the Sun (this is called aphelion) around July 2 each year (94.8 million miles = 152.6 million km).

WarningWarning NEVER LOOK NEVER LOOK

DIRECTLY AT DIRECTLY AT THE SUN!THE SUN! Looking at the Looking at the Sun can blind Sun can blind you or cause you or cause cataracts. cataracts.

• Our Sun is a second or third generation star. Second generation stars do not just burn hydrogen, they also burn heavier elements, like helium and metals, and were formed from supernova explosions.

• supernova = an exploding star

Structure of the Sun

Structure of the Sun

                                                                                                                                                                    

The CoreThe Core

The temperature is The temperature is

roughly 15 million °C. roughly 15 million °C. At this temperature, At this temperature, nuclear fusion occurs, nuclear fusion occurs, turning four hydrogen turning four hydrogen nuclei into a single nuclei into a single helium nucleus plus a helium nucleus plus a LOT of energy. LOT of energy.

Nuclear FusionNuclear Fusion

Nuclear fusion is an Nuclear fusion is an atomic reaction in atomic reaction in which many nuclei (the which many nuclei (the centers of atoms) centers of atoms) combine together to combine together to make a larger one make a larger one (which is a different (which is a different element). element).

• The result of this process is the release of a lot of energy. (Suns are powered by nuclear fusion, mostly converting hydrogen into helium. In this process, 4 hydrogen nuclei combine to form a single helium nucleus; about 0.3% of the original mass is converted into energy.

• Although the nuclear output of the sun is not entirely consistent, each second the Sun converts about 600,000,000 tons of hydrogen nuclei into helium nuclei.

• These fusion reactions convert part of these atoms' mass (roughly 4 million tons) into energy, and release an enormous amount of this heat and light energy into the Solar System.

• In these fusion reactions, the Sun loses 4 million tons of mass each second.

• The Sun will run out of fuel in about 5 billion (5,000,000,000) years. When this happens, the Sun will explode into a planetary nebula, a giant shell of gas that will destroy the planets in the Solar System (including Earth).

Radiation Zone

• The next layer out from the core is this zone which emits radiation. This radiation diffuses outwards. The temperature ranges from 15 million °C to one million °C. It may take photons of radiation millions of years to pass through the radiative zone, as they gradually make their way outwards.

The Convective Zone

• The Convective Zone: In this next layer, photons continue to make their way outwards via convection (towards lower temperature and pressure). The temperature ranges from one million °C to 6,000 °C.

CONVECTIONConvection is the transfer of heat by circulation through a gas or liquid.

The Chromosphere• The Chromosphere: This

reddish layer is an area of rising temperatures. The temperature ranges from 6,000 °C (at lower altitudes) to 50,000 °C (at higher altitudes). This layer is a few thousand miles (or kilometers) thick. It appears red because hydrogen atoms are in an excited state and emit radiation.

• The Chromosphere is visible during solar eclipses

The Photoshpere

• This is the lower atmosphere of the Sun and the part that we see (since it emits light at visible wavelengths). This layer is about 300 miles (500km) thick. The temperature is about 5,500 °C.

The CoronaThe Corona

This is the outer layer This is the outer layer of the Sun's of the Sun's atmosphere. The atmosphere. The corona extends for corona extends for millions of miles and millions of miles and the temperatures are the temperatures are tremendous, reaching tremendous, reaching one million °C. one million °C.

The QuizThe Quiz

1. Is the Sun a star, a planet, or a 1. Is the Sun a star, a planet, or a nebula? nebula?

2. Is the Sun solid, liquid, or gaseous?2. Is the Sun solid, liquid, or gaseous?

3. During what month is the Sun closest 3. During what month is the Sun closest to the Earth? to the Earth?

4. Where is the Sun hottest?4. Where is the Sun hottest?

5. Where is the Sun coolest?5. Where is the Sun coolest?

6. What element is most plentiful on the 6. What element is most plentiful on the Sun?Sun?

7. What element was named after the 7. What element was named after the Sun? Sun?

8. What is the primary atomic reaction 8. What is the primary atomic reaction that occurs within the Sun that converts that occurs within the Sun that converts hydrogen atoms into helium atoms? hydrogen atoms into helium atoms?

9. How old is the Sun? 9. How old is the Sun?

10. Are sunspots hotter or colder than the 10. Are sunspots hotter or colder than the surrounding areas? surrounding areas?