Lecture 1
Spring 2009

Key Concepts:

  1. Course Introduction
  2. What is the Scientific Method?
  3. Math tools: power of 10 and scientific notation
  4. Scales of the Universe and Units

Introduction: astronomy is " the science of the heavenly bodies"

Scientific Method

"is an organized approach to explaining observed facts
with a model of nature, subject to the constraint that
any proposed model must be testable
and that the model must be modified or discarded
if it fails the tests."

Power of Ten and Scientific Notation

  • Powers of 10

    Scales of the Universe and Units

    • Distance
      • meter: unit of length equal to 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p(10) and 5d(5) of the krypton-86 atom

      • km: 1000 meters (103 m)

      • AU: astronomical unit (150 million km or 1.5 x 108 km)

      • Lyr: light year (distance traveled by light in 1 year)

        • c = 300,000 km per second (3 x 105 km/s)
        • 1 yr = 32 million seconds (3.2 x 107 s)
        • 1 Lyr = (3 x 105 km/s) x (3.2 x 107 s) = 10 x 1012 km
    • More on the Universe
    • Size
      • Earth radius: 6,378 km (or 6.4 x 103 km)

      • Sun's radius: 700,000 km (or 7 x 105 km)

      • Solar system: about 100 AU or about 10 light hour

      • Nearest star: about 4.4 light year

      • Milky Way Galaxy: 50,000 lyr

      • Local Group: 1.5 million lyr

      • Visible Universe: 15 billion lyr


    • Mass
      • Earth mass: mass of Earth = 6 x 1027 gram

      • Solar mass: mass of Sun = 2 x 1033 gram


    • Luminosity = energy output per second
      • Solar luminosity: 4 x 1026 watts


    • Astronomy Computational Classroom
    • Quiz 1

    Reading assignment for next lecture: Chapter 2 (p.26-34)