Worksheet 4.2 (Teacher's Answers)




How are the stars we see at night related to the Sun? How are they different?

The Sun is a star, but the Sun is very close and the stars are very, very far away.



How big is the Sun relative to Earth? How far away is it?

The Sunís diameter is 109 times larger than Earth. The volume is over 1 million times greater than Earthís. The Earth is 150 million km from the Sun (or 93 million miles, or 8.3 light-minutes, or 1 Astronomical Unit, or 11,700 Earth diameters, or 390 times the distance between the Earth and the Moon).


How do the density and temperature of the Sun vary from the center outward?

The Sun is very dense at its core, and the density steadily decreases out toward its surface, where it is less dense than Earth’s atmosphere. It continues to decrease out into the corona where the density is about 1 particle per cubic centimeter. The temperature at the core is 15 million Kelvin and decreases steadily out to about 5,000 K at the photosphere. It then rises again to about 1 million Kelvin in the corona. [Student answers need not be this detailed]


How does the Sun produce the energy it needs to stay hot?

It uses nuclear fusion at its core to stay hot.



Why does the Sun shine?

The Sun shines because it is hot.



What parts of the Sun are revealed by using invisible forms of light to observe it?

The chromosphere is visible using UV and H-Alpha (which is visible). The corona is visible using visible light, extreme ultraviolet, and x-ray light.


Can plasma move freely in the presence of a magnetic field? Why not?

No, plasma cannot move freely in a magnetic field because it is charged gas. When charged gas moves it creates an electrical current. Electrical currents are constrained to move along magnetic lines of force.



What are sunspots?

Sunspots are cooler places than average on the Sun’s photosphere where strong magnetic fields inhibit convection.



What happens to the Sun’s magnetic field with time, and how does that affect the number of sunspots and solar flares?

The Sun’s magnetic field gets twisted up due to the differential rotation of the Sun. As it gets twisted, parts of it poke through the surface, forming sunspots and causing solar flares. The magnetic field gets the most twisted every 11 years and flips polarity.

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