The Galilean Moons of Jupiter

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Julius Koza, Slowakije Sterrekundig Instituut,
Universiteit Utrecht Postdoc at Solar Physics
Department Dutch Open Telescope team of prof. R.
J. Rutten http//dot.astro.uu.nl/ DOT in full
beauty DOT observation of Sunspots
office Buys Ballot Laboratorium
7th floor, room no. 762 E-mail J.Koza_at_astro.u
u.nl telephone 030 - 253 5235
www.astro.sk/koza/practicum.html
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The Galilean Moons of Jupiter

• Astronomical Practicum, January 22 - 26, 2007

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Origin of the word planet

• the ancients knew just seven planets including
  the (Sun, Moon), Mercury, Venus, Mars, Jupiter,
  and Saturn
• planets (from Greek) mean wanderers implying
  their apparent drift among fixed stars

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History and founders of celestial mechanics
celestial mechanics - the branch of astronomy
concerned with the application of Newtons laws
of motion to the motions of heavenly bodies
"If I have seen further (than you and Descartes)
it is by standing upon the shoulders of Giants."
I.
Newton in a letter to Robert Hooke, February 5,
1676
Isaac Newton (1643-1727)
Galileo Galilei (1564-1642)
Johannes Kepler (1571-1630)
Tycho Brahe (1546-1601)
Nicolaus Copernicus (1473-1543)
Claudius Ptolemay (100 - 170 AD)
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Mysterious planetary kinks
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Claudius Ptolemy (100 AD - 170 AD)

• synthesized and extended Hipparchus's system of
  epicycles and eccentric circles to explain his
  geocentric theory of the solar system.
• Ptolemy's system involved at least 80 epicycles
  to explain the motions of the Sun, the Moon, and
  the five planets known in his time.
• He believed the planets and sun to orbit the
  Earth in the order
• Moon, Mercury, Venus, Sun, Mars, Jupiter,
  Saturn.
• This geocentric system predicted the positions of
  the planets accurately enough for naked-eye
  observations.

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Ptolemys epicycles, deferents and excenters
Ptolemy described in his book Almagest geocentric
system and gave various arguments to prove that,
in its position at the center of the universe,
the Earth must be immovable.
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Nicolaus Copernicus (1473-1543)

• replaced the geocentric universe of Ptolemy with
  one that was centered on the Sun, with only the
  Moon orbiting the Earth
• his heliocentric system was quite
  contra-intuitive
• the explanation for retrograde motion in this
  system
• planets move in circular orbits
• the planets further from the sun are moving more
  slowly than those closer to the sun (decreasing
  orbital velocity with the distance)
• De revolutionibus orbium coelestium, libri VI (On
  the Revolutions of the Heavenly Spheres, six
  books published in 1543)

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The problems of Copernican heliocentrizm

• Objections against heliocentrizm known from
  antique

• If the Earth actually spun on an axis (as
  required in a heliocentric system to explain the
  diurnal motion of the sky), why didn't objects
  fly off the spinning Earth ?
• If the Earth was in motion around the sun, why
  didn't it leave behind the birds flying in the
  air ?
• If the Earth were actually on an orbit around the
  sun, why wasn't a parallax effect observed ?

• Moreover, Copernican heliocentric system
• was no more precise in predicting of planetary
  motion than Ptolemy's model
• also needed the eccentrics, epicycles, and
  equants of Ptolemaic cosmology
• but mathematically simpler and more elegant

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Johannes Kepler (1571-1630)

• aimed at finding the lows of planetary motions
  able to explain the best observations available
  at those times
• Tycho Brahe (1546-1601)- the best naked eye
  observer of pre-telescopic era
• laborious and obsessed Kepler inherited large
  archive of Tychos observations of the postions
  of the planets
• after twenty years of painstaking trial-and-error
  attempts at making some sense out of the data he
  finally arrived at his three laws of planetary
  motion subsequently published in two books
  Astronomia Nova (New Astronomy, 1609) - first
  and second law
• Harmonices Mundi (The Harmonies of the World,
  1619) - third law
• using these laws Kepler was able to predict the
  planetary motion with unprecedented precision and
  in perfect agreement with observations

The statue of Brahe and Kepler in Prague
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Keplers laws of planetary motion

• Keplers laws are empirical laws, it means they
  were found from an analyze of observations.
• Kepler's elliptical orbit law
• 1. Each planet moves in an elliptical orbit, with
  the sun at one focus of the ellipse.
• Kepler's equal-area law
• 2. A line from the sun to a given planet sweeps
  out equal areas in equal times.
• Kepler's law of periods
• 3. The periods of the planets are proportional to
  the 3/2 powers of the semi major axis lengths of
  the orbits.

• Kepler was first man in the world knowing the
  right answer on the question
• HOW THE PLANETS MOVE ?
• But he still couldnt answer WHY is it so.

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Two different periods !

• The synodic period Tsyn the period with respect
  to the Sun
• The sidereal period Tsid the revolution period
  with respect to the stars
• Always holds Tsyn gt Tsid
• Periods of the Moon
• Synodic month (new moon to new moon) 29.53 days
• Sidereal month (fixed star to fixed star) 27.32
  days

Third Keplers law tells about sidereal period T
!!!
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Declination ? what is it ?

• Declination ? is the angular distance to a point
  on a celestial sphere measured north or south
  from the celestial equator in degrees.