General Astronomy

Instructor:

Prof. Kaaret

702 Van Allen Hall

E-mail: philip-kaaret [at] uiowa.edu

Phone: 335-1985

Class website:

http://astro.physics.uiowa.edu/~kaaret/genastro11s

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 exam 250

Homework 200

Laboratory (up to 25 points extra credit) 250

Total 1000

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/sTypical walking speed is 3 mph = 1.3 m/s

Earth

Radius of earth or R is 6.4106 m

Sun

Radius of Sun or R is 7108 m

Earth to Sun

Distance from Earth to Sun is 1.51011 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 3107 seconds.

• A year is the time scale of the Earth’s orbit.• The velocity scale for the Earth’s orbital motion is

Velocity = 2 1.51011 m/3107 s = 3104 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 4.11016 m

Define light-year = ly = 9.46 1015 m

Distance from Sun to Alpha Centauri is 4.3 ly

to Center of Milky Way

Distance to Center of our galaxy is 2.61020 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 71015 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 2.61020 m/71015 s = 2105 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 2.41022 m

or 2.6 106 ly

to edge of Observable Universe

Distance to edge of observable universe is 1.31026 m or 1.4 1010 ly

Big bang Milky 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?