ASTR 111 – 003 Fall 2007Lecture 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 SunCh28: The Search for Extraterrestrial Life

Ch7: Comparative Planetology ICh8: Comparative Planetology IICh9: The Living EarthCh10: Our Barren MoonCh11: Mercury, Venus and MarsCh12: Jupiter and SaturnCh13: Satellites of Jupiter & SaturnCh14: Uranus, Neptune and BeyondCh15: Vagabonds of Solar System

Ch1: Astronomy and the UniverseCh2: Knowing the HeavensCh3: Eclipses and the Motion of the MoonCh4: Gravitation and the Waltz of the PlanetsCh5: The Nature of LightCh6: Optics and Telescope

Energy from the Sun sustains life on the Earth

Our Star, the SunChap. 16

Basic Facts• Diameter: 1,400,000 km• Distance to Earth: 1 AU = 1.5 X 108 km • Light travel time: 500 seconds• Angular size: 30 arcmin • Effective Surface Temperature: 5800 K

Thermonuclear reactions• Sun’s total energy output: 1026 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 c2

•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

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

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

Dynamic Atmosphere

Space Weather: the EffectsSpace Weather: the EffectsSpace Weather: the EffectsSpace Weather: the Effects

Human Space Exploration

Satellite Operation

Aurora Communication and Navigation

Aviation

Power

The Search for Extraterrestrial Life

Chap. 28

The State of the Universe•Age: 13.7 billion years

•Size:

•Composition: •dark energy: 73%•dark matter: 23%•ordinary matter: 4%

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

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

The Drake equationEstimate how many civilizations may inhabit our Galaxy: about 10

=1 per year

=1

~0.1

~1

~1

~1

~100 years

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…