Astronomy 161 -- Fall 2009 (Prof. Stanek)
Midterm 1 Study Guide (Friday, Oct. 9th)
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There will be 50 questions on the Midterm Exam, which will count for
20% of the final grade.

Classes to review:

The Celestial Sphere
Season & Calendar
Moon Phases & Eclipses
From Ptolemy to Copernicus
Tycho, Kepler, & Galileo

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Key Concepts:

The Celestial Sphere 
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(1) The sky as seen from Earth is divided into 88 constellations.
(2) It is convenient to pretend the stars are attached to a celestial
    sphere.
(3) The celestial sphere appears to rotate about the celestial poles
    (1 day).
(4) The Sun appears to move west to east relative to stars (1 year).
(5) The Moon appears to move west to east relative to stars (1 month).

Season & Calendars 
-------------------

(1) The cause of the seasons is the tilt of the Earth's rotation axis
    relative to its orbit around the Sun.
(2) The day is based on the time between one noon and the next.
(3) The year is based on the time between one vernal equinox and the
    next.
(4) The moon (month) is based on the time between one new moon and the
    next.

Moon Phases & Eclipses 
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(1) Lunar phases change as we see more or less of the Moon's sunlit
     half.
(2) The Moon rotates about its axis as it revolves around the Earth.
(3) The sidereal month=27.3 days; the synodic month=29.5 days.
(4) A lunar eclipse occurs when the Moon passes through the Earth's
    shadow.
(5) A solar eclipse occurs when the Earth passes through the Moon's
    shadow.

From Ptolemy to Copernicus 
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(1) Aristotle (4th cent BC) showed that the Earth is round.
(2) Greek astronomers developed a geocentric model for the universe.
(3) Ptolemy (2nd cent) used epicycles to explain retrograde motion of
    planers.
(4) Copernicus (16th cent) proposed a heliocentric model for the
    universe.
(5) In the model of Copernicus, retrograde motion is easily explained.

Tycho, Kepler, & Galileo 
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(1) Tycho Brahe made accurate measurements of planetary motion.
(2) Planetary orbits are ellipses with the Sun at one focus.
(3) A line between planet & Sun sweeps out equal areas in equal times.
(4) The square of a planet's orbital period is proportional to the
    cube of its average distance from the Sun.
(5) Galileo made telescopic observations supporting the heliocentric
    model.