Section 1 Review 

Here are my suggestions about what you need to do for preparing your exam #1:

• Review all the textbook units covered and your class notes as well as the copies of my lectures.
• Redo previous quiz and homework questions, at least those you had trouble with. 

Following are what I consider the most important topics covered in this section.

Naked Eye Astronomy and Tools of Astronomy

• The Scale of the Universe

  • Relative scales of planets, plant orbits, the Sun and other stars, galaxies, etc.

  • Powers of 10 and orders of magnitude

  • Scientific notation (e.g., 1 A.U. = 1.5 x 10⁸ km)

  • Names of basic units and conversions (e.g., meter, nm, ly, K, degree, arcminute, arcsecond, etc.).
    

  • Metric system, which allows for much easier calculations.

  • The speed of light. The relation between light travel time and distance (How is a light-year defined? What is a year, astronomically?).

• Apparent Motions of the Sun and Stars;  Seasons

  • Daily motion of the Sun and stars

    • Sun and stars move from east to west during day (Earth's rotation)

  • The celestial sphere -- a model of the apparent Universe

    • north and south celestial poles

    • celestial equator

    • zenith 

    • horizon 

    • altitude, latitude
       

  • Annual motions of the Sun and stars

    • Sun slips from west to east among stars about 1^o per day or 30^o per month (Earth's orbit around Sun); as a result, a constellation rises about two hours earlier after a month (What is the use of constellations today anyway?).

    • ecliptic (zodiac constellations) 

    • Sun appears to move along ecliptic -- north of celestial equator in our summer, south of celestial equator in winter.

• Seasons on Earth

  • Tilt of Earth's axis (23.5^o) causes Sun's motion north-south-north throughout year. (So if the Earth were tipped less than the angle, seasons on Earth would be less severe.) The autumnal equinox, vernal equinox, summer solstice, and winter solstice. 

  • Seasons are result of (1) angle of sunlight and (2) duration of daylight due to tilt

  • Seasons have nothing to do with distance from Sun

• Phases of the Moon; Tides; Eclipses

  • Phases of Moon caused by our changing view of Moon, illuminated by Sunlight, as the Moon orbits Earth once/month. When does the full moon set? When does the first quarter moon rise? Does the Moon rise at the same time each day?

  • Tides caused by difference in Moon's pull on front of Earth vs. on back of Earth --> stretches out the oceans into high and low tides.

    When do you expect a low tide during the Full Moon?

  • Solar eclipse: Moon blocks Sun (seen from Earth) -- Moon casts shadow on Earth.

  • Lunar eclipse: Earth blocks Sun (seen from Moon) -- Earth casts shadow on Moon (When do we expect to a partial lunar eclipse?)

  • You always see the same half of the moon sphere. As Moon revolves around Earth once, it rotates in the opposite direction once. Why?

• Planetary Motions

  • Planets move mostly in ecliptic

  • Inferior planets (Venus, Mercury) stay close to Sun

  • Superior planets (esp. Mars) sometimes move in retrograde loops 

• Historical Astronomy/Gravity and Orbits

  • Greeks founded basis of Western science

    • Aristotle -- geocentric Universe, the perfect heaven, and the uniform circular motion.

    • Ptolemy -- added epicycles to explain retrograde loops, etc.

  • Copernicus -- heliocentric Universe, but only believed circle motion

  • Tycho Brahe -- made accurate observations (e.g., a supernova and planet positions)

  • Kepler -- used Tycho's data, supported Copernican view, plus:

    • All planets move in ellipses, the Sun at one focus

    • planets move faster closer to Sun --> sweep out equal areas in equal times

    • P²_yr = R³_AU (The equation applies to objects in the solar system, including comets.)

      How would the orbital period of a planet change if its average orbital radius were increased by a factor of 2?

  • Galileo -- used telescope to see moons around Jupiter, sunspots, stars in the Milky Way, phases of Venus, craters on Moon, "ears" or companion stars on Saturn; supported Keplerian view. Why were these discoveries controversial and important?

  • Newton -- studied all of the above,  he found the three laws:

    • inertia (constant and straight motion unless a force is inserted)

    • F=ma (a --- acceleration that is the rate of change in speed, direction, or both)

    • reaction (equal and opposite forces)

    Plus Universal Law of Gravity: F=Gm₁m₂/r². If the Moon were three times closer to the Earth, how would the gravitational force between them would change?

    Newton realized how gravity works to cause Moon to "fall" towards Earth without getting closer.

• Light: The Electromagnetic Spectrum 

  Electromagnetic radiation

  • is a form of energy

  • can travel through a vacuum
    

  • includes radio, microwave, infrared, optical, ultraviolet, X-ray, and gamma ray radiation

  • can be described as waves with length , frequency , and speed c (Can you  convert between and ?)

  • can also be described by photons with energy E=h

  • has colors determined by or

  • can be dispersed into its component colors by a prism or a grating

  • brightness f 1/d²

• Temperature and Black Body Radiation

  • Temperature  is a measure of the average speed of the particles in a gas 

    • units: Kelvin; 

    • absolute zero (no motion of atoms and no heat)
      

  • thick gases or solid bodies warmer than absolute zero glow = black body radiation, which is continuous emission from thermal motion of electrons

  • Wien's law tells wavelength of peak of black body spectrum (hotter --> bluer; colder --> redder): _peak = 2.9/T, with in mm and T in Kelvin

  • Stefan-Boltzman law (hotter --> brighter, colder --> fainter): the integrated radiation energy (heat) L T⁴

• Atoms and Spectral Lines

  • atoms consist of nuclei (protons and neutrons) and electrons, which are bound together by electromagnetic force

  • electrons orbit nuclei in discrete (not random) energy levels

  • if electron absorbs photon with right energy, can jump to higher energy level --> absorption lines in spectrum

  • electron may later emit same color photon and jump back down to original level, or emit different color photons matching different transitions --> emission lines in spectrum

  • Transition between energy levels of an atom may also caused by a collision with another atom or electron (e.g., collisional excitation or ionization)

  • each element (H, He, C, N, O....) has different energy levels --> unique fingerprint of spectral lines