General Astronomy Instructor: Prof. Kaaret 702 Van Allen Hall philip-kaaret [at] uiowa.edu Phone: Class website:

Course topics Sun, stars Black holes, neutron stars Galaxies Cosmology

Course elements Lecture Homework In-class exams Final exam Laboratory (must pass lab to pass course)

Lectures and Homework Lectures: MWF 1:30 pm – 2:20 pm, LR70 VAN Textbook: Foundations of Astrophysics, Ryden and Peterson Homework: About once per week, usually due on Mondays, do in groups of 2-3 if that helps.

Laboratory Lab: M or T 7:00 pm – 9:00 pm, 666 VAN 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.

Grading One-hour exams (3 exams, each 100 points)300 Final exam250 Homework200 Laboratory (up to 25 points extra credit)250 Total1000

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.

Sizes are in meters

People Height of (small) person is about 1 m

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

Earth Radius of earth or R  is 6.4  10 6 m

Sun Radius of Sun or R  is 7  10 8 m

Earth to Sun Distance from Earth to Sun is 1.5  m This is one “Astronomical Unit” = 1 A.U.

Earth’s Orbit The Earth makes one revolution about the Sun in one year, or about 3  10 7 seconds. A year is the time scale of the Earth’s orbit. The velocity scale for the Earth’s orbital motion is Velocity = 2   1.5  m/3  10 7 s = 3  10 4 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.

Sun to Nearest Star Distance from Sun to nearest star is 4.1  m Define light-year = ly = 9.46  m Distance from Sun to Alpha Centauri is 4.3 ly

to Center of Milky Way Distance to Center of our galaxy is 2.6  m or 28,000 ly

Sun’s Orbit The Sun makes one revolution about the center of the Milky Way in 230 million years, or about 7  seconds. This is the `time scale’ of the Sun’s 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 Sun’s orbital motion is Velocity = 2   2.6  m/7  s = 2  10 5 m/s = 200 km/s This is an order of magnitude faster than the orbit of the Earth around the Sun.

to Nearest (big) Galaxy Distance to nearest (big) galaxy is 2.4  m or 2.6  10 6 ly

to edge of Observable Universe Distance to edge of observable universe is 1.3  m or 1.4  ly

Big bangMilky Way forms Sun and planets form Oldest known life - single cell First multicellular life Carl Sagan’s “Cosmic Calendar” The history of the Universe in one year

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 Earth’s rotational speed at the equator from the Earth’s 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?