Gravitation and Satellites Eclipses and Tides Black Holes Keplers Laws

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Gravitation and SatellitesEclipses and
TidesBlack HolesKeplers Laws
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Projectile or Satellite?
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Circular Orbit Total energy is constant No work
is done on planet Speed is constant
Elliptical Orbit Total energy is constant Work
is done on planet (to change speed)
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Tidal Bulges on Earth
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• The moon is twice as effective as the sun at
  producing tides on earth
• Tides are produced by the differential
  gravitational attraction of the moon on the near
  and far sides of the earth
• Two tidal bulges are produced (near and far side)
• Position of tidal bulges is constant
• the earth rotates to carry us through these
  positions
• we see two high tides and two low tides per day
• The two high tides in one day are usually unequal
  due to the tilt of earths axis

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Two Types of Tides

• Spring tide
• Sun, moon, earth lined up
• Highest of the high tides
• New or full phase of moon
• Neap tide
• Sun, moon, earth at 90 degrees
• Lowest of high tides
• 1st or 3rd quarter phase of moon

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Other Tides

• Tides in solid earth
• Average rise/fall of ground is 25 cm
• Tides in atmosphere
• In ionosphere, electric currents alter magnetic
  field, affect cosmic ray penetration

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Solar and Lunar Eclipses

• Solar Eclipse
• At new moon
• No longer than 7.5 min
• Seen in path of about 270 km wide
• Seen by only a few people
• Total, partial, or annular
• Rarely seen, not rare in occurrence

• Lunar eclipse
• At full moon
• No longer than 1 h 40 min
• Total or partial
• Seen by all on dark side of earth
• At totality, red color
• Commonly seen

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Solar Lunar eclipses which is which?
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Eclipses should occur twice each month. Why
dont they?
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Umbra and Penumbra during eclipses
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Lunar Eclipse-3 exposures APOD Jan 25, 2000 by
Stephen Barnes
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Solar Eclipse
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Solar Eclipse
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How are Black Holes Detected?
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Known Black Holes (and artists conceptions)
http//images.google.com/imgres?imgurlhttp//scie
nce.nasa.gov/headlines/images/blackhole/blackhole-
swirl.jpgimgrefurlhttp//science.nasa.gov/headli
nes/y2001/ast12jan_1.htmh360w452sz88hlens
tart4tbnid8fL59zt6O0YLOMtbnh101tbnw127pre
v/ima
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http//antwrp.gsfc.nasa.gov/apod/ap060701.html ht
tp//antwrp.gsfc.nasa.gov/apod/ap060528.html http
//antwrp.gsfc.nasa.gov/apod/ap060427.html http/
/antwrp.gsfc.nasa.gov/apod/ap060412.html
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In the Arms of NGC 1097 R. Jay GaBany
(Cosmotography.com) NGC 1097s center harbors a
massive black hole.
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http//www.youtube.com/watch?vdUp_KUdNKJs http/
/www.youtube.com/watch?vY4dusPXL1vI
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Satellite Motion
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g v2/r for circular orbit!
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Satellite Game
http//www.mcasco.com/p1aso.html http//home.cvc.
org/science/kepler.gif
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• Kepler's laws of planetary motion
• Planets move on elliptic orbits with the
• sun at a focal point. More generally satellites
• of the sun (planets, comets, asteroids) move on
• conic sections (ellipses, parabolae, hyperbolae)
• with the sun at a focal point.
• 2. The line connecting a planet with the sun
• sweeps out equal areas in equal periods of time.
• 3. Comparing different planets, the squares of
• their orbital periods are proportional to the
• cubes of the long axes of their orbits.