Lecture 36

1. The Sun. Tools of Astronomy. The Sun (continued) Telescopes and Spacecrafts Lecture 36 Chapter 17.1  17.7

2. Hydrogen Fusion in the Sun The proton-proton chain

3. How does the Light Comes Out? Photons are created in the nuclear fusion cycle. They collide with other charged particles and change their direction (random walk). They also decrease their energy while walking. It takes ~10 million year to get outside. The random bouncing occurs in the radiation zone (from the core to ~70% of the Sun’s radius). At T<2 million K, the convection zone carries photons further towards the surface.

4. The Sun’s Internal Structure

5. Solar Neutrino Neutrino is a subatomic particle. It is a by-product of the solar proton-proton cycle. It barely interacts with anything. Counts of neutrino coming from the Sun are crucial to test our knowledge about solar physics. Neutrino observatories use huge amounts of different substances to detect nuclear reactions with neutrino. So far theory predicts more neutrino than is seen.

6. The Super Kamiokande Experiment Information Sonic Boom

7. Observations of Solar Neutrino The GALLEX detector Gran Sasso, Italy The Sudbury Observatory Ontario, Canada

8. Sunspots and Other Solar Activity Sunspots have T~4,000 K, cooler than the 5,800 K surrounding plasma. Sunspots are kept together by strong magnetic fields. Usually sunspot appear in pairs connected by a loop of magnetic field lines. The loops rising into the chromosphere or corona may appear as solar prominences. Solar flares are events releasing a lot of energy where magnetic field lines break.

9. Sunspot Close-Up

10. The Sunspot Cycle Observations of the Sun since the beginning of the telescopic era revealed that the number of sunspots gradually rises and declines. An average period is 11 years (from 7 to 15 years). The magnetic fields in sunspots reverse their direction when a cycle is over. No sunspots were observed in 16451715, when a Little Ice Age took place in Europe and America.

11. The Sunspot Cycle

12. Summary of the Sun The Sun shines with energy generated by fusion of hydrogen into helium in its core. Gravitational equilibrium determines the Sun’s interior structure and maintains a steady nuclear burning rate. The Sun is the only star near enough to study it in great detail.

13. Collecting Light with Telescopes Telescopes are giant eyes, collecting more light than we could with our naked eyes Telescopes are characterized by 2 key properties Light-collecting area (depends on the telescope size) Angular resolution (how much detail we can see in the telescope’s images)

14. Telescope Design Two basic designs: Refracting and Reflecting telescopes Refracting telescope uses transparent glass lenses to focus the light (from Galileo’s small telescopes to a 1-m refractor)

15. Refractors

16. Refractors

17. Telescope Design Reflecting telescopes use precisely curved mirrors Most contemporary telescopes are reflectors Primary mirror gather and focuses the light Secondary mirror reflects the light to a convenient location

18. Reflectors

19. Reflectors

20. Uses of Telescopes Imaging - pictures of celestial objects Spectroscopy - dispersing light into a spectrum Timing - tracking time variations of the light Atmosphere affects observations - light pollution, turbulence Turbulence can be corrected by adaptive optics

21. Types of Telescopes Optical and Infrared telescopes Radio telescopes (use metal “mirrors”) Interferometeres (link several separate telescopes together to improve angular resolution)

22. Observatories

23. Radiotelescopes

24. Satellites • First satellite  1957 Soviet Sputnik • First astronomical satellites  late 1960’s • The Hubble Space Telescope (HST)  1990 • The X-ray Chandra Observatory  1999 • The Spitzer Space (IR) Observatory  2003

25. Satellites