1. ASTR 111 – 003 Fall 2007 Lecture 14 Dec. 3, 2007 Introducing Astronomy (chap. 1-6) Introduction To Modern Astronomy I: Solar System Planets and Moons (chap. 7-15) Sun and Life: Highlights (Chap. 16 & 28) Ch16: Our Star: the Sun Ch28: The Search for Extraterrestrial Life Ch7: Comparative Planetology I Ch8: Comparative Planetology II Ch9: The Living Earth Ch10: Our Barren Moon Ch11: Mercury, Venus and Mars Ch12: Jupiter and Saturn Ch13: Satellites of Jupiter & Saturn Ch14: Uranus, Neptune and Beyond Ch15: Vagabonds of Solar System Ch1: Astronomy and the Universe Ch2: Knowing the Heavens Ch3: Eclipses and the Motion of the Moon Ch4: Gravitation and the Waltz of the Planets Ch5: The Nature of Light Ch6: Optics and Telescope

2. Energy from the Sun sustains life on the Earth Our Star, the Sun Chap. 16

3. Basic Facts Diameter: 1,400,000 km Distance to Earth: 1 AU = 1.5 X 10 8 km Light travel time: 500 seconds Angular size: 30 arcmin Effective Surface Temperature: 5800 K

4. Thermonuclear reactions Sun’s total energy output: 10 26 watts Can not be chemical energy (only last 10,000 years) Can not be gravitational contraction (only last 25 million years) Energy from nuclear reaction –Corresponds to a reduction of mass according Einstein’s mass-energy equation: E = m c 2

5. The Sun’s energy is produced by hydrogen fusion: a sequence of thermonuclear reactions in which four hydrogen nuclei combine to produce a single helium nucleus; called proton-proton chain reaction Thermonuclear reactions

6. 4 H  He + energy + neutrinos Mass of 4 H > Mass of 1 He In every second, 600 million tons of hydrogen converts into helium to power the Sun At this rate, the Sun can last for about 10 billion years It is now 4.6 billion year old It will continue the hydrogen burning for at least another 5 billion years. Thermonuclear reactions The sun itself is extremely stable. It controls the climate of the Earth

7. Dynamic Atmosphere However, the Sun’s atmosphere is extremely dynamic

8. Dynamic Atmosphere

9. Space Weather: the Effects Human Space Exploration Satellite Operation AuroraCommunication and Navigation Aviation Power

10. The Search for Extraterrestrial Life Chap. 28

11. The State of the Universe Age: 13.7 billion years Size: Composition: dark energy: 73% dark matter: 23% ordinary matter: 4%

12. Chemical building blocks of life All life on Earth is based on carbon- based compounds, called organic molecules These organic molecules occur naturally in the interstellar clouds of gas and dust, called nebula, throughout galaxies

13. Liquid Water Liquid water may be needed for Earth-like life Besides Earth, at least two worlds in our solar system—the planet Mars and Jupiter’s satellite Europa—may have had liquid water

14. The Drake equation Estimate how many civilizations may inhabit our Galaxy: about 10 =1 per year =1 ~0.1 ~1 ~100 years

15. ATA: Allen Telescope Array of 350-dishes when completed. 42 dishes now working Dedicated to search for extraterrestrial intelligent life (SETI) Seth Shostak: “I think we will find signals from intelligent civilizations by 2025” Search…Search…