The

The sun is a huge ball of hot, luminous gas. In its core, hydrogen is converted to helium, releasing energy that is felt on Earth as heat and light. the sun has existed in this form for some 4.6 billion years and should stay the same for another 5 billion or so years.

inside the sun the sun is immense; its diameter is 109 times that of earth, and it contains 99 percent of all the material in the solar system. It is made mainly of hydrogen (about 73.5 percent) and helium (about 25 percent) with tiny amounts of around 90 other elements. Gravity keeps the

Photosphere

The Sun's visible surface

Core

Where nuclear reactions occur

Radiative zone

Where energy travels in the form of photons

Convective zone

A region where energy is carried by convection cells

Chromosphere_

An irregular layer of atmosphere above the photosphere

THE SUN'S INTERIOR

Hydrogen is converted to helium in the Sun's core. Energy produced moves toward the surface by radiation and then by convection, before leaving the Sun through the photosphere.

Core

Where nuclear reactions occur

Radiative zone

Where energy travels in the form of photons

Convective zone

A region where energy is carried by convection cells

sun's gas together, pulling it toward the center. the temperature increases and the pressure builds up with depth. Pressure tries to push the gas out and prevent it from becoming ever more tightly packed. As long as the balance between gravity and pressure is maintained, the sun will keep its present size and globe shape.

In the core, which contains about 60 percent of the sun's mass, it is about 27 million °F (15 million °C). Here, nuclear reactions convert the hydrogen to helium at the rate of about 600 million tons each second. In the process, nearly five million tons is released as energy. the sun is not solid, so—unlike earth, which spins as a whole—some parts of the sun spin at different speeds from others. the equator spins in 25 days, while the polar regions take about 10 days longer.

the sun's surface the visible surface of the sun is a layer 300 miles (500 km) deep, called the photosphere. It is made of cells of rising gas called granules, which give it a mottled appearance like that of orange peel. these convection cells, which are about 620 miles (1,000 km) across, are short-lived and constantly renew themselves. spicules are short-lived jets of gas that stand out from the surface. they look tiny compared with the

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