Astronomy 201: Cosmology Prof. Jill Bechtold Graduate TA: Ken Wong Pick up hard copy of syllabus...

Astronomy 201: Cosmology

Prof. Jill BechtoldGraduate TA: Ken Wong

Pick up hard copy of syllabusPick up HW #1

http://boojum.as.arizona.edu/~jill/astro201.html

The Textbooks21st Century Astronomy: Stars and Galaxies by Hester et al. 3rd Edition.

Unbound version available at UA bookstore for low cost -- $45.50

However, this version is not refundable or re-sellable

The bound edition is available through Amazon.com for $71.

An ebook version is also available

“Stars and Galaxies” is a subset of “21st Century Astronomy”

$45 or $71 $115

Two other books

Dancing With the Universe: From Creation Myths to the Big Bang, by Marcelo Gleiser

paperback, $23 new, $5-10 used

From Eternity to Here: The Quest for the Ultimate Theory of Time, by Sean Carroll

paperback will come out in October Bookstore: $17, Amazon $11

Do I need to buy the books?

• Class notes will be posted• Exams will be on lecture material• If you like to also read the material in a

textbook, get the Hester et al. book• If you like to read prose, the other books are

readable and enjoyable – especially if you like history, culture and philosophy

What Is Modern Astronomy?

• Science of the nature of everything outside of the Earth’s atmosphere: planets, stars, interstellar gas, galaxies, etc.

• What is the content of the Universe? – What is its history? What is its future?

• How do humans fit in?

The science that studies the history & future of the Universe is called

“cosmologycosmology”

“kosmos” = order, harmony

“logos” = word, law"My goal is simple. It is complete understanding of the universe, why it is as it is and why it exists at all. "

-- Stephen Hawking

Our Cosmic Address

STEWARD OBSERVATORY

Ca. 1930

Steward ObservatoryTHE UNIVERSITY OF ARIZONA

Steward ObservatoryThe University of Arizona

TUCSON

Steward ObservatoryThe University of ArizonaTucsonARIZONA

Steward Observatory, The University of ArizonaTucson, ArizonaUNITED STATES, NORTH AMERICA

Steward Observatory, The University of ArizonaTucson, ArizonaUnited States, North America

EARTH

EARTH

• Planet• Diameter = 7900 miles• Mass = 6x1024 kilograms• Age = 4.5 billion years = 4.5 x 109 years

= 4,500,000,000 years

Earth has one moon, which orbits it

Earth-Moon distance = 240,000 miles

or 30 Earth Diameters

The Moon

Steward Observatory, The University of ArizonaTucson, ArizonaUnited States, North AmericaEarth

SOLAR SYSTEM(Not to scale)

SUN, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (Pluto)

Solar system to scale:

SUN

THE SUN

Visible light image

THE SUN• Star, produces energy by nuclear fusion (Hydrogen helium)

THE SUN• Star, produces energy by nuclear fusion (Hydrogen helium) • 93 million miles from Earth• 93 million miles = 1 Astronomical Unit, or A.U.

More on units of distance:More on units of distance:

• Instead of miles, kilometers, etc. astronomers often use light seconds, light minutes, light years

More on units of distance:


• 1 Light Year = the distance light travels in one year

More on units of distance:


• 1 Light Year = the distance light travels in one year

• 1 Light Year = 5.9 x 1012 miles

THE MOON IS ABOUT 1.3 LIGHT SECONDS FROM EARTHTHE MOON IS ABOUT 1.3 LIGHT SECONDS FROM EARTH

THE SUN IS ABOUT 8.3 LIGHT MINUTESFROM EARTH

Practical matters: Astronomers use scientific notation to write large & small numbers.

1000 =

1,000,000,000 =

0.001 =

2,200,000 =

103

109

10-3

2.2 x 106

1 light minute = the distance light travels in one minute

1 light year = the distance light travels in one year = almost 10 trillion kilometers or 6 trillion miles (one trillion = 1012 = 1,000,000,000,000)



Because light takes time to travel through space, when we look farther away in distance, we look farther back in TIME.



Because light takes time to travel through space, when we look farther away in distance, we look farther back in TIME.

The farthest we can see in space is 13.7 billion light years, because we think the Universe is 13.7 billion years old.

Orbit of Quaor (Q) and Pluto (P) versus the planets

STARS NEAR THE SUN

Nearest Star to Sun: Alpha Centauri

• Triple star in S. hemisphere



• 4.2 light years from the Sun




• Alpha Centauri A and Alpha Centauri B are orbiting each other with period 80 years, separation 23 Astronomical Units.




• Alpha Centauri A and Alpha Centauri B are orbiting each other with period 80 years, separation 23 Astronomical Units.

• Proxima Centauri is 13,000 AU from Alpha Centauri A and B.

Space Travel

Freeway speed

Jetliner speed

Concorde Speed (Mach 2)

Spacecraft Speed

Speed

Freeway speed 75 mph

Jetliner speed 500 mph


1350 mph

Spacecraft Speed40,000 mph

Speed Time to get to Mars

Time to getTo Jupiter

Freeway speed 75 mph 80 years 600 years

Jetliner speed 500 mph 12 years 90 years


1350 mph

4.4 years 33 years


2 months 1.5 years


Freeway speed 75 mph 80 years

Jetliner speed 500 mph 12 years


1350 mph

4.4 years


2 months



Time to get to Saturn

Freeway speed 75 mph 80 years 600 years 1200 years

Jetliner speed 500 mph 12 years 90 years 180 years


1350 mph

4.4 years 33 years 66 years


2 months 1.5 years 3 years



Time to get to Saturn

Time to get to Alpha Centauri

Freeway speed 75 mph 80 years 600 years 1200 years 38 million years

Jetliner speed 500 mph 12 years 90 years 180 years 6 million years


1350 mph

4.4 years 33 years 66 years 2 million years


2 months 1.5 years 3 years 70,000 years

Back to our COSMIC ADDRESS

Steward Observatory, The University of ArizonaTucson, ArizonaUnited States, North AmericaEarthSolar System

Milky Way Galaxy: The Sun is one star of many in the Milky Way

The Milky Way as seen from Earth

Spiral Galaxy

Our Milky Way, Plus many “dwarf” satellite galaxies

The LOCAL GROUP

The AndromedaGalaxy

The other big spiral galaxy in the Local Group

About 2.5 millionLight years fromThe Milky Way

The Local Group is on the edge of the VIRGO CLUSTER OF GALAXIES

A photograph of the center of the VIRGO CLUSTER OF GALAXIES

SUPER-CLUSTERS

OUR COSMIC ADDRESS

Steward Observatory, The University of ArizonaTucson, ArizonaUnited States, North AmericaEarthSolar System

Milky Way GalaxyLocal Group of GalaxiesVirgo Cluster of GalaxiesLocal Supercluster of Galaxies

The UNIVERSE

Astronomy 201: Cosmology Prof. Jill Bechtold Graduate TA: Ken Wong Pick up hard copy of syllabus...

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