PES 106        Spring 2003

General Astronomy II

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Lecture Notes:

Introduction, Scientific Method and Observation

Textbook: Preview, Overview 1 and Chapter 1, Section 1

Introduction:

  • What is Astronomy ?
    • a science - includes physics, chemistry, geology, biology ...
    • a human experience - beauty, inspirer of poetry and song

     

  • Definition:
    • The study of the Universe.
      • What is it ? ....................... Observation
      • How does it work ? ............. Understanding

 

  • Related ideas: (not covered here)
    • philosophy / religion .....................Why is there a Universe ?
    • astrology .................................. How does the Universe guide our lives (if it does) ?

Scientific Method:

  • Science => Scientific Method
    • Observation
    • Hypothesis
    • More Observation
    • Theory
      • Explains all existing observations
      • predicts new phenomena
    • More Observation
  • If Observations disagree with theory
    • check observation for validity
    • get a new theory
  • Scientists do not deal with "truth"
    • work with models
    • models change as we learn more
    • if we are lucky, the models are getting closer to the truth

Observation

What can WE see ? (with our eyes but no telescopes)

lots of astronomy was developed before telescopes

 

OBJECT
MOTION
COMMENTS

1. stars

fixed with respect to one another, slowly rotate together

individual stars, clusters, Milky Way

2. moon

moves quickly with respect to the stars

large, changes shape in a repeating pattern

3. planets (wanderers)

move slowly with respect to the stars

sometimes move backwards

4. comets

move slowly with respect to the stars

long tails, appear suddenly

5. meteors

move VERY quickly

very bright, short lived

6. Sun

moves quickly with respect to other stars

in daytime sky, very bright

7. man-made satellites

move very quickly

8. empty space

not really so empty !

We will concentrate on objects outside our Solar System this semester.

To look for man-made satellites in the sky, check out this NASA web site: http://liftoff.msfc.nasa.gov/toc.asp?s=Tracking

Distances in Astronomy

HARD to determine with just our eyes
moon is bigger than stars => closer

meteors are smaller than moon - but they are closer

=> size of object does not really help

We can measure distances ........ and they are LARGE !!

  • Units of distance:
    • kilometer (km)
      • a little more than half a mile
    • light year (ly)
      • distance light can travel in one year
      • = 9.46 x 1012 km
      • about 1/4 the distance to the nearest star (other than our Sun)
    • parsec (pc)
      • = 3.26 ly = 3.09 x 1013 km
      • approximately the distance between stars

Demonstration of distances in the Universe

An exercise on distances is available at: http://janus.astro.umd.edu/astro/distance.html

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