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
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)
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:
• Instead of miles, kilometers, etc. astronomers often use light seconds, light minutes, light years
• 1 Light Year = the distance light travels in one year
More on units of distance:
• Instead of miles, kilometers, etc. astronomers often use light seconds, light minutes, light years
• 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)
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.
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.
The farthest we can see in space is 13.7 billion light years, because we think the Universe is 13.7 billion years old.
Nearest Star to Sun: Alpha Centauri
• Triple star in S. hemisphere
Nearest Star to Sun: Alpha Centauri
• Triple star in S. hemisphere
• 4.2 light years from 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.
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.
• 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
Concorde Speed (Mach 2)
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
Concorde Speed (Mach 2)
1350 mph
4.4 years 33 years
Spacecraft Speed40,000 mph
2 months 1.5 years
Speed Time to get to Mars
Freeway speed 75 mph 80 years
Jetliner speed 500 mph 12 years
Concorde Speed (Mach 2)
1350 mph
4.4 years
Spacecraft Speed40,000 mph
2 months
Speed Time to get to Mars
Time to getTo Jupiter
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
Concorde Speed (Mach 2)
1350 mph
4.4 years 33 years 66 years
Spacecraft Speed40,000 mph
2 months 1.5 years 3 years
Speed Time to get to Mars
Time to getTo Jupiter
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
Concorde Speed (Mach 2)
1350 mph
4.4 years 33 years 66 years 2 million years
Spacecraft Speed40,000 mph
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