PES 105        Fall 2001 General Astronomy I

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Lecture Notes:

Lecture 1: Introduction, Scientific Method and Observation

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

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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) ?

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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

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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 within our Solar System this semester. These are rows 2-6.

The moon, planets and comets do not produce light of their own. They all shine from reflected sun light.

The Planets and Moon follow a similar path across the sky. => "zodiac"

See Figure OV1.7 for a view of the zodiac

See Figure OV1.9 for how planets move relative to the stars

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

We observe patterns to the motions.............. things repeat.

=> motions can be predicted (more on this soon)

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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
  • astronomical unit (AU)
    • average distance from Sun to Earth
    • about 100,000,000 km

Demonstration of distances in the solar system.

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

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