Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine [e-mail]

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Astronomy 101The Solar SystemTuesday,
Thursday230-345 pmHasbrouck 20Tom
Burbinetomburbine_at_astro.umass.edu
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Course

• Course Website
• http//blogs.umass.edu/astron101-tburbine/
• Textbook
• Pathways to Astronomy (2nd Edition) by Stephen
  Schneider and Thomas Arny.
• You also will need a calculator.

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Office Hours

• Mine
• Tuesday, Thursday - 115-215pm
• Lederle Graduate Research Tower C 632
• Neil
• Tuesday, Thursday - 11 am-noon
• Lederle Graduate Research Tower B 619-O

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Homework

• We will use Spark
• https//spark.oit.umass.edu/webct/logonDisplay.dow
  ebct
• Homework will be due approximately twice a week

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HW 3 (due today)

• 10 questions
• In Assessment in Spark

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Hw 4 (due Monday)

• Under Assessments in Spark

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Exam 1

• Next Thursday
• Material we cover today will be on the exam

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New Discovery

• http//www.cnn.com/2009/TECH/space/09/16/new.rocky
  .planet/index.html

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Nicholas Copernicus (1473-1543)

• Copernicus came up with a model that the Earth
  revolves around the Sun
• Similar to what Aristarchus (310 230 BC)
  thought 2000 years before
• However, Copernicus models did not match
  observations since he wanted everything to
  arouind in perfect circles

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Tycho Brahe (1546-1601)

• Tycho Brahe was the greatest naked eye observer
  of all time
• He lived before the invention of the telescope
• His observations of the alignment of Jupiter and
  Saturn occurred two days later than when
  predicted by Copernicus
• Tycho came up with a model where the planets
  orbit the Sun but the Sun orbits Earth

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Johannes Kepler (1571-1630)

• Tried to match circular orbits to Tychos data
• Couldnt do it
• Because Tychos observations were so good, Kepler
  had to come up with a new model

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Kepler was trying to match an orbit to Tychos
observations of Mars

• If I believed that we could ignore these eight
  minutes of arc, I would have patched up my
  hypothesis accordingly. But, since it was not
  permissible to ignore, those 8 minutes pointed to
  the road to a complete reformation in astronomy.
• Kepler came up with his 3 laws of planetary motion

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Keplers 1st Law

• The orbit of each planet about the Sun is an
  ellipse with the Sun at one focus (there is
  nothing at the other focus)

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Differences between ellipses and circles
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Eccentricity (e)

• e distance between the two foci/length of major
  axis
• e of circle is 0
• The larger e becomes, the more eccentric the orbit

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Definitions

• Perihelion planet closest to the Sun
• Aphelion planet farthest from the sun
• Semimajor axis (a) the average of a planets
  perihelion and aphelion distances

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Keplers 2nd law

• As a planet moves around its orbit, it sweeps out
  equal areas in equal times.
• This means that the planet travels faster when it
  is nearer the Sun and slower when it is farther
  from the Sun

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• http//surendranath.tripod.com/Applets/Dynamics/Ke
  pler/Kepler1Applet.html

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Keplers 3rd Law

• More distant planets orbit the Sun at slower
  average speeds, obeying the precise mathematical
  relationship
• p2 a3
• where p is a planets orbital period in years
  and a is the average distance from the Sun in
  astronomical units (AU).

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Calculations

• The period for the Earth to go around the Sun is
  1 year
• The average distance of the Earth to the Sun is
  1 Astronomical Unit (AU)

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How long does it take Jupiter to go around the Sun

• If Jupiter is 5.2 Astronomical Units from the
  Sun, how long does it take Jupiter to go orbit
  the Sun once
• p2 a3 5.23 140.6
• p v140.6 11.9 years

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Another example

• Mercury is 0.4 Astronomical Units from the Sun.
• How long does it take Mercury to orbit the sun
  once?
• A) 1 year
• B) 3 months
• C) 9 months
• D) 5 years

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The calculation

• p2 a3 0.43 0.064
• p v0.064 0.25 years

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• An asteroid takes 8 years to go around the Sun
• How far is the asteroid away from the Sun?
• A) 1 AU
• B) 3 AU
• C) 4 AU
• D) 8 AU

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The calculation

• a3 p2 82 64
• a (64)1/3 4 AU

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You can calculate a planets orbital speed

• Since you know a planets orbital distance
• And you know its orbital time
• You can calculate a planets average orbital speed

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Orbits

• all the planets orbit the Sun in a
  counterclockwise direction (but they do not orbit
  it at the same rate).
• The Earth rotates counterclockwise

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Arguments against the Sun being the center of the
solar system

• 1) If the Earth was moving, objects such as birds
  and clouds would be left behind as the Earth
  moved
• 2) The heavens must be perfect and unchanging.
  Noncircular orbits do not fit this model
• 3) Stellar parallax would be observable

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Galileo Galilei (1564-1642)

• He was able to figure out answers to these
  arguments
• 1) Things in motion tend to remain in motion.
• 2) He used a telescope to see sunspots on the Sun
  and features on the Moon.
• 3) Galileo found that stars were more numerous
  and more distant than imagined

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He also

• He discovered the moons of Jupiter and saw that
  they were orbiting Jupiter
• Proving that bodies could orbit other bodies
  besides the Earth

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Galileo also found that Venus orbited the Sun
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Who came up with the first understanding of how
gravity and forces really work?
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Isaac Newton (1642-1727)
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http//www.hulu.com/watch/63319/cosmos-the-harmony
-of-the-worlds
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Any Questions?