Chapter 18 - The Sun The Sun is a star, a glowing ball of gas held together by its own gravity and powered by nuclear fusion at its center.

Our Sun is a “typical” star Our Sun is a “typical” star. It is in the middle range of stellar mass, radius, brightness, and composition. The Sun contains no solid material.

The part of the Sun that we see with (or without) a telescope is the solar disk.

The photosphere is the “surface” of the Sun The photosphere is the “surface” of the Sun. Above the photosphere is the lower atmosphere of the Sun, called the chromosphere.

Far beyond the chromosphere is the thin outer atmosphere, the corona.

Further out in space, extending out to the gas giants, is the solar wind.

The layers within the Sun begin with the photosphere as the surface.

Below the photosphere is the convection zone, where the heat is transferred from the interior to the surface.

Within the convection zone is the solar interior at the center of which is the solar core where the Sun’s nuclear fusion occurs.

Diameter - 1.4 x 106 km 100x Earth Volume - 1 million times Earth’s Mass - 2.0 x 1033 g 300,000 x Earth’s

Average Density - 1.4 g/cm3 (similar to the Jovian planets) About 1/4 Earth’s density.

Temperature - 6000K in the photosphere

Solar Constant – the amount of solar energy reaching Earth per unit area per unit time. 1.4 x 106 erg/cm2/sec

(1 erg is less than 1/10 the energy expended by a jumping flea)

A sunbather’s body has a surface area of about 0 A sunbather’s body has a surface area of about 0.5 m2 (unless it is Coach Huggins). That is 5000 cm2. The amount of heat received by this sunbather is about 7 x 109 ergs/sec.

That is equivalent to 700 watts That is equivalent to 700 watts. This is about the amount of heat given off by a typical electric room heater or ten household light bulbs.

The total energy given off by the Sun each second is its luminosity and is 4 x 1033 erg/sec.

This is equal to 100 billion 1-megaton nuclear bombs each second This is equal to 100 billion 1-megaton nuclear bombs each second. This would be 4 x 1026 watts or 4 trillion trillion 100-watt light bulbs shining simultaneously.

This would cost 1019 US dollars per second.