Astronomy

Chapter Eighteen: Earth, the Moon, and the Sun

• 18.1 The Earth and Its Moon

• 18.2 Earth Cycles

• 18.3 The Sun

Investigation 18B

• What causes the seasons?

Earth’s Seasons

18.3 The Sun

• The Sun is a star.

• A star is a giant, hot ball of gas held together by gravity.

• The Sun is medium-sized compared with other stars in the universe.

Approximately 1 million planet Earths could fit inside the Sun!

18.3 The Sun• Gravity squeezes the

atoms in the core of a star so tightly that they fuse together in a reaction called nuclear fusion.

• In the process, huge amounts of energy are given off.

18.3 Anatomy of the sun

• The corona is the outermost layer of the sun’s atmosphere, extending millions of kilometers beyond the sun.

• Sunspots are areas of gas that are cooler than the gases around them.

18.3 Features of the sun

• Occasionally, large “loops” of gas called prominences can be seen jumping up from groups of sunspots.

18.3 Features of the sun

• Solar wind is an electrically charged mixture of protons and electrons.

• Auroras, called the northern lights, occur when layers of our atmosphere are energized by solar winds.

Research Connection

Solar Observatory

• The staff of Big Bear Solar Observatory study the sun, solar phenomena, and the solar atmosphere.

Activity

• Scientists have been studying the sun, its behavior and its relationship to the Earth.

• Graph the month of the year versus the distance of Earth to the Sun using a spreadsheet program.

Distance from Earth to the Sun