The Sun

1. The Sun Section1 – Structure of the Sun

2. 29-1 Objectives • Explain how the sun converts matter into energy in its core • Compare the radiative and convective zones of the sun • Describe the three layers of the sun’s atmosphere

3. The Sun’s Energy • Historically, where did people think the sun’s energy came from? • Fire or burning coal • Composition of the Sun • Light is broken into a spectrum of visible light using a spectrograph • Wide, deep lines show significant amounts of certain elements in sun’s composition • Hydrogen over 75% • Hydrogen and Helium about 99% of sun’s mass

4. Nuclear Fusion • Figure 2, page 756 • Process of combining nuclei of small atoms to form more-massive nuclei – Energy is released at each step • Step 1: protons collide and fuse, positron is released, makes proton-neutron pair in nucleus • Step 2: another proton combines with proton-neutron pair make nucleus with 2 + and 1 N. • Step 3: two nuclei collide and fuse together • Final Product: Helium nucleus

5. Mass Changing Into Energy • E = mc2 • E = energy, m = mass, and c = speed of light. This equation showed scientists how the sun could produce so much energy without burning up! • Neutrino is the subatomic particle given off when two protons are forced to bond together. • Reach Earth’s surface in about 8 minutes

6. The Sun’s Interior • The Core – not very large compared to the sun’s overall mass, only 25%. • Temperature = 15,000,000C • Entirely made of ionized gas • Where nuclear fusion of H into He occurs • The Radiative zone – between the core and convective zone where energy moves by radiation • Temperature = 2,000,000C – 7,000,000C • Energy moves outward in form of electromagnetic waves

7. The Sun’s Interior • The Convective Zone – region of sun’s interior that is between radiative zone and photosphere and energy is carried towards the surface by convection • Temperature = 2,000,000C • Convection: transfer of energy by moving matter • Hot gases are moved by a convection current and carry energy outwards to surface • Hot gases rise and carry energy then they cool and begin to sink again. (just like boiling water)

8. The Sun’s Atmosphere • The Photosphere – innermost layer, means “sphere of light” • Made of gases that have risen from convective zone and temps are around 6,000C • Energy is mostly given off as visible light • It is what we see from Earth’s surface because the other layers of the atmosphere are not visible unless under certain conditions • Dark spots are cooler areas with temps around 3,800C and are known as sun spots • Figure 5, page 759

9. The Sun’s Atmosphere • The Chromosphere – thin layer of the sun that is just above the photosphere and glows a reddish color during eclipses. • This is the only time the outer layers of the sun’s atmosphere is visible to viewers on Earth • “color” sphere – red is typical color given off by H • Temps 4,000C – 50,000C • Jets of hot gas move outward from photosphere and rapidly cool, some jets reaching 16,000 km in height

10. The Sun’s Outer Parts • The corona is the outermost layer of the sun’s atmosphere, a huge region of gas with temps above 1,000,000C • It has a strong magnetic field that traps most subatomic particles • Electrons and electrically charged particles called ions only escape into space as the corona expands and these particles stream out forming solar winds • Not visible unless during eclipses, Figure 6 on page 760

11. The Sun Section 2 – Solar Activity

12. 29-2 Objectives • Explain how sunspots are related to powerful magnetic fields on the sun • Compare prominences, solar flares, and coronal mass ejections • Describe how the solar wind can cause auroras on Earth

13. Solar Activity • Gases have large volumes and the individual molecules are constantly moving. • They don’t all move at the same speed • The sun rotates faster near the equator than it does at the poles • Rotation at equator = 25.3 Earth days • Rotation at poles = 33 Earth days • Average rotation of the sun = once every 27 days

14. Sunspots • Figure 1, page 761 • Dark areas of the photosphere that are cooler than the surrounding areas and have STRONG MAGNETIC FIELDS • Produced by movements of gas in the convective zone and the sun’s rotation • Still very bright even with dark appearance • Magnetic fields slow the rate of convection, lowering the area’s temps up to 3,000C • Granulation – grainy appearance of photosphere • Large diameter, could be several time the size of Earth

15. Sunspot Cycle • Figure 2, page 762 • Sunspots gave evidence that the sun rotated • Numbers and positions of sunspots vary in a recognizable pattern – cycle every 11 years • Minimum # begins the cycle and spots begin to appear in groups near equator • Increase until reach a max of 100+ • Slowly begin to decrease with any new ones appearing closer to equator and old ones at higher latitudes (near the poles) begin to disappear

16. Solar Ejections • Solar-activity cycle – caused by the changing solar magnetic field • Types of solar ejections • Prominences • Solar Flares • Coronal Mass Ejections

17. Solar Ejections • Prominences are clouds of glowing gas that arc along lines of magnetic forces • Opposites attract • Solar flares are sudden outward eruptions of electrically charged particles • Coronal Mass Ejections are particles of coronal gas that escape into space from the sun • These particles can affect Earth and this is known as geomagnetic storms • These storms can cause power outages, damage satellites, compasses won’t work, interfere with animal migratory patterns

18. Auroras • Colored lights produced by interactions between solar winds (charged particles from space) and Earth’s magnetosphere • Aurora borealis – Northern lights • Aurora australis – Southern lights • 100 – 1,000 km above Earth’s surface • Can also be seen on Jupiter and Saturn http://www.youtube.com/watch?v=icugqEEOgkg