1. The Sun
Unit 1B : Astronomy

2. First…we have to discuss light
Information about universe
Light emitted from stars and other bodies in space
Electromagnetic spectrum = arrangement of waves according to their wavelengths and frequencies
We see visible part of spectrum

3. Visible Light A range of waves with various wavelengths
Passed through a prism
Violet bent more than blue
Blue bent more than green
Etc.

4. Spectroscopy
Study of the properties of light that depend on wavelength
absorption spectrum = visible light is passed through a cool gas under low pressure

5. Absorption Spectrum
Each element or compound in gaseous form produces unique set of spectral lines
Studying a star
Lines indicate which elements --> star’s chemical composition

6. Remember the Doppler Effect?
Light from a source moving away from you appears redder
Waves are lengthened
Moving toward you appears bluer
Waves are shortened
Determine whether a star or other body in space is moving away from or toward Earth
Measured from the dark lines in spectra and comparing them with a standard spectrum

7. Intro to the Sun “Average” star Earth’s primary source of energy
Only star whose surface we can study
Diameter = 109 Earths
Mass = 332,000 times of Earth

8. Our Sun is a Star

9. Structure of the Sun Sun is made of gas 4 parts
No clear boundaries between layers
4 parts
Solar interior
Photosphere
Chromosphere
corona

10. Photosphere Visible surface Radiates most of the sunlight we see
Layer of gas
Grainy texture --> granules
Composition = 90% hydrogen, almost 10% helium
Dark lines of absorption spectrum

11. Chromosphere Above the photosphere Thin layer of hot gases
Can see during a total solar eclipse (red rim)
Light from photosphere is blocked out

12. Corona Outermost portion of the solar atmosphere Weak
Envelope of gases > extend a million kilometers from sun

13. Corona
Solar wind = streams of protons and electrons ejected at high speed from the corona
Travel through solar system and are lost to space
Alters appearance of bodies in the solar system
Earth’s magnetic field doesn’t allow them to reach our surface -- > do affect our atmosphere

14. Solar Wind

15. Sunspots Dark spots on the surface of the sun
Temperature is less than the surrounding solar surface
Number of sunspots observable vary in an 11-year cycle
Increases to maximum (100) --> then decrease to minimum
Motion of sunspots --> sun rotates about once a month
Not all parts rotate at the same speed (gaseous)

16. Sunspots

17. Prominences
Concentration of gases often appearing as arches extending beyond corona
Sometimes can erupt  matter escapes Sun’s atmosphere

18. Solar Flares Sudden eruption Above sunspot cluster
Release lots of energy (UV, radio, X-ray)
Atomic particles released --> reach Earth day later (affect long- distance radio communications)
Auroras = bright display of light caused by solar radiation interacting with the upper atmosphere at the poles
Following strong solar flare

19. Solar Flares

20. Solar Interior Source of energy = nuclear fusion
Combining of the nuclei of lighter elements to form a heavier element
Energy released because some matter is converted to energy

21. Introduction to Nuclear Energy

22. Process of nuclear fusion
Converts four hydrogen nuclei into the nucleus of a helium atom
Lots of energy released!
4 hydrogens = amu; 1 helium = amu
Missing mass! (.029 amu)

23. Process of nuclear fusion
E = mc2
c = speed of light
Speed of light is very high (300,000 km/sec) --> amount of energy released from small mass is very high
One pinhead of hydrogen to helium > burning thousands of tons of coal

24. Nuclear Fusion in the Sun
Small percentage of hydrogen is converted to energy
Helium forms the solar core --> grows

25. Future of the Sun Will the sun run out of hydrogen fuel?
Last another 100 billion years
Sun will grow
Engulf Earth
Sun can exist in its stable state for 10 billion years
Already 4.5 billion years old