General Astronomy

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General Astronomy

• Instructor
• Prof. Kaaret
• 702 Van Allen Hall
• E-mail philip-kaaret at uiowa.edu
• Phone [phone]
• Class website
• http//astro.physics.uiowa.edu/kaaret/genastro07s

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Course topics

• Sun, stars
• Black holes, neutron stars
• Galaxies
• Cosmology

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Course elements

• Lecture, homework
• Laboratory
• Observing

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Lectures and Homework

• Lectures MWF 230 pm 320 pm, LR70 VAN
• Textbook The Cosmic Perspective Stars,
  Galaxies, and Cosmology, 4th Edition, by Bennett,
  Donahue, Schneider, and Voit
• Homework About once per week, usually due on
  Mondays, do in groups of 2-3 if that helps.

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PRS (Personal Response System)

• Each of you should have a PRS unit.
• We will be using a student feedback technology
  called PRS during most lectures. provide
  anonymous feedback in class
• PRS transmitters (looks like an old calculator)
  with an individual code are sold in a package
  with the textbook.
• Every student must have a PRS unit and bring it
  to each class.

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Laboratory

• Lab M or T 700 pm 900 pm, 666 VAN
• Lab manual Imaging the Universe, byMutel Cook
• Lab will consist of several canned labs and a
  research project. Get started on the research
  project early. It is possible to get extra
  credit for an imaginative or extensive research
  project.

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Observing

• On the roof of Van Allen Hall on Monday
  Thursday evenings when the sky is clear.
• There is an observing sheet on the class web
  site. Print it out and bring it to clear sky
  patrol. Hand in partially completed lists to
  Prof. Kaaret to have credit recorded.
• Each student must earn at least 50 observing
  points to pass the class. Start observing early
  and go observing often.
• It is possible to get extra credit for observing
  more than the required 50 points.

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Grading
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Scales in length, time, and motion

• Astrophysics requires knowledge of the Universe
  on the entire range of length scales from
  sub-nuclear to cosmological.
• Knowing the typical size and time scales of a
  system gives significant insight into that
  system.
• Astronomical time scales can be extremely long.

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Sizes are in meters
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People
Height of (small) person is about 1 m
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People

• If the small person spins around, she can make
  one revolution in about 1 second.
• The typical time scale for people, i.e. how fast
  they react to some event (how long does it take
  you to slam on the brakes if the car in front of
  you stops), is of order seconds.
• The typical velocity scale for people is
• Velocity length/time 1 m/1 s 1 m/s
• Typical walking speed is 3 mph 1.3 m/s

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Earth
Radius of earth or R? is 6.4?106 m
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Sun
Radius of Sun or R? is 7?108 m
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Earth to Sun
Distance from Earth to Sun is 1.5?1011 m This is
one Astronomical Unit 1 A.U.
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Earths Orbit

• The Earth makes one revolution about the Sun in
  one year, or about 3?107 seconds.
• A year is the time scale of the Earths orbit.
• The velocity scale for the Earths orbital motion
  is
• Velocity 2? ? 1.5?1011 m/3?107 s 3?104 m/s
• 30 km/s 70,000 mph
• This is much faster than Earth bound speeds
• A speeding bullet travels at about 1000 m/s
  2000 mph.

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Sun to Nearest Star
Distance from Sun to nearest star is 4.1?1016
m Define light-year ly 9.46 ?1015 m Distance
from Sun to Alpha Centauri is 4.3 ly
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to Center of Milky Way
Distance to Center of our galaxy is 2.6?1020 m or
28,000 ly
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Suns Orbit

• The Sun makes one revolution about the center of
  the Milky Way in 230 million years, or about
  7?1015 seconds.
• This is the time scale of the Suns orbit and a
  reasonable time scale for interactions of
  galaxies (how long does a galaxy take to react to
  an event like a collision with another galaxy).
• The velocity scale for the Suns orbital motion
  is
• Velocity 2? ? 2.6?1020 m/7?1015 s 2?105 m/s
• 200 km/s
• This is an order of magnitude faster than the
  orbit of the Earth around the Sun.

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to Nearest (big) Galaxy
Distance to nearest (big) galaxy is 2.4?1022 m or
2.6 ?106 ly
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to edge of Observable Universe
Distance to edge of observable universe is
1.3?1026 m or 1.4 ?1010 ly
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Carl Sagans Cosmic Calendar The history of the
Universe in one year
Big bang
Milky Way forms
Sun and planets form
Oldest known life - single cell
First multicellular life
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Review Questions

• If one made a scale model of the Sun and its
  closest neighbor star which could fit in a room,
  say with a length of 5 m, what would be the
  diameter of the Sun? Of the Earth?
• How long does it take light to travel from the
  Sun to the Earth?
• Find Earths rotational speed at the equator from
  the Earths diameter and the length of a day.
• Starting at Earth and driving on an interstellar
  highway at 75 mph, how long would it take to
  reach Alpha Centauri? The center of the Milky
  Way?