Astronomy 170: The Physical Universe Prof. Jill Bechtold Graduate TAs: Johanna Teske, Megan Reiter All Students: Pick up 3 white handouts Honors: Pick

Astronomy 170: The Physical Universe

Prof. Jill BechtoldGraduate TAs: Johanna Teske, Megan Reiter

All Students: Pick up 3 white handoutsHonors: Pick up 4th handout on black cart

The Textbook: Recommended, Not Required

The Cosmic PerspectiveBy Bennett, Donahue, Schneider, & Voit

6th edition

5th edition OK, but there are always updates

An ebook version is also available

Do I need to buy the book?

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

textbook, get the Bennett et al. book• New books come with a key to use the

publisher’s web site, Mastering Astronomy, which has “flash cards”, quiz questions, and other study aides.

Honors Credit

• If you want honors credit for this class, be sure you are signed up for Section 3.

• If you are in Section 2 and want honors credit, please bring a change of class form for me to sign as soon as possible

• Trip to Sky Center on Mt. Lemmon• We will have an organizational meeting later

in the semester

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?

"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

Goals of this course

• Survey of current state-of-the-art astronomy and astrophysics

• Science literacy in the physical sciences; current topics

• See how working research scientists think

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

Documents

Astronomy 170: The Physical Universe Prof. Jill Bechtold Graduate TAs: Johanna Teske, Megan Reiter All Students: Pick up 3 white handouts Honors: Pick