Transcript Aug24 - University of Arizona

Astronomy 201: Cosmology
Prof. Jill Bechtold
Graduate TA: Ken Wong
Pick up hard copy of syllabus
Pick up HW #1
http://boojum.as.arizona.edu/~jill/astro201.html
The Textbooks
21st 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
“cosmology”
“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 Observatory
THE UNIVERSITY OF ARIZONA
Steward Observatory
The University of Arizona
TUCSON
Steward Observatory
The University of Arizona
Tucson
ARIZONA
Steward Observatory, The University of Arizona
Tucson, Arizona
UNITED STATES, NORTH AMERICA
Steward Observatory, The University of Arizona
Tucson, Arizona
United 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
The Moon
Earth-Moon distance
= 240,000 miles
or 30 Earth Diameters
Steward Observatory, The University of Arizona
Tucson, Arizona
United States, North America
Earth
SOLAR SYSTEM
(Not to scale)
SUN, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (Pluto)
Solar system to scale:
SUN
THE SUN
• Star, produces energy by nuclear fusion
(Hydrogen  helium)
• 93 million miles from Earth
• 93 million miles = 1 Astronomical Unit, or A.U.
Visible light image
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 EARTH
THE SUN IS ABOUT 8.3 LIGHT MINUTES
FROM EARTH
Practical matters: Astronomers use scientific
notation to write large & small numbers.
3
10
1000 =
1,000,000,000 =
109
0.001 = 10-3
2,200,000 = 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.
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.
• Proxima Centauri is 13,000 AU from Alpha Centauri A and B.
Space Travel
Speed
Time to
get to
Mars
Time to get
To 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
2 months
1.5 years
3 years
70,000 years
Spacecraft Speed
40,000
mph
Back to our COSMIC ADDRESS
Steward Observatory, The University of Arizona
Tucson, Arizona
United States, North America
Earth
Solar 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 Andromeda
Galaxy
The other big
spiral galaxy in
the Local Group
About 2.5 million
Light years from
The 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
SUPERCLUSTERS
OUR COSMIC ADDRESS
Steward Observatory, The University of Arizona
Tucson, Arizona
United States, North America
Earth
Solar System
Milky Way Galaxy
Local Group of Galaxies
Virgo Cluster of Galaxies
Local Supercluster of Galaxies
The UNIVERSE