29:52 Announcements

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2952 Announcements Monday Sept 13

• PRS
• Registration registration website available
• http//deimos.physics.uiowa.edu/prs
• See email (sent this morning)
• Will try using Friday (trial run, not for credit)
• Exam 1
• Wednesday in class.
• Chapter 1-4,6 (note change!)
• Chapter 5 will not cover.
• Course website has been updated to

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Review Keplers 3 laws

• All planetary orbits are ellipses
• Planets sweep out equal areas on equal time
• This implies that planets move fastest at
  perihelion (closest to Sun) and slowest at
  aphelion (farthest from Sun)
• Orbital period (P) and sem i-major axis (a
  radius of orbit for nealry circular orbits) are
  related by

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Keplers third law illustrated
Where P is in years, a in AU
Suppose a planet is discovered with a semi-majpr
axis 10 AU. What is its orbital period in Earth
years?
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The Earths atmosphere blocks most of the
electromagnetic spectrum ? absorption by
ozone, oxygen, carbon dioxide and water vapor
? VISIBLE, RADIO, SOME INFRARED can pass
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The weather/air conditions are also
important ? dust, particles in the air can
absorb EM radiation ? water vapor is a major
absorber rain! clouds! (humidity like right
now outside) ? distortion of waves by the
atmosphere ? seeing is how well the
atmosphere allows you to image details good
seeing conditions, bad seeing seeing usually
measured in arcseconds ? bottom line HIGH,
DRY, REMOTE observing sites!
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Keck I II telescopes optical telescopes 10-m
mirror (made of smaller pieces) Mauna Kea, Hawaii
elevation 14,000 feet
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Highest, driest telescope site ( 16,400
feet) Atacama desert, Northern Chile Future
site of millimeter array telescope ALMA
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Artists conception of ALMA telescope 64 12-m
telescopes!
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Angular Resolution of Telescopes

• Angular Resolution of telescope with diameter D
  or radio interferometer with spacing D

D, ? are in the same length units ? is in
arcseconds
Example 1 large single dish Arecibo D 300m, ?
10cm (0.1 m), ? 66 arcsec
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Arecibo Radio Telescope (Puerto Rico)Worlds
largest single dish radio telescope
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Very Large Array (VLA)(Central New Mexico)
Worlds most powerful radio interferometer (27
antennas, 25m diameter)
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The Very Long Baseline Array (VLBA) An array of
10 Identical Radio telescopes
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The Resolution of the Arecibo Telescope, the VLA,
and the VLBA
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Hubble Space Telescope beat the atmosphere
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• Hubble Space Telescope
• optical telescope
• 2.4-m mirror
• in low-earth orbit
• 368 miles above Earth
• orbits every 90 minutes

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Spacecraft Communications Data Pipeline
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X-rays Chandra X-ray Observatory
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X-rays will pass through normal mirrors to focus
X-rays, use grazing incidence
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SIRTF Space InfraRed Telescope Facility (in
earth orbit an infrared Hubble)
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SOFIA Stratospheric Observatory for Infrared
Astronomy telescope implanted in a 747 aircraft,
flies at 40,000 feet
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Spacecraft vs. Ground Based Observing

• PROS for Spacecraft
• Access to wavelengths that are unavailable on the
  ground
• Atmospheric effects gone
• Development of sophisticated tech.

• CONS for Spacecraft
• Can not fix/test as easily
• Risk with rocket launch
• Much much more costly!
• Lifetime is usually shorter
• Upgrades much more difficult

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Practice questions for exam 1

• Suppose you are an inhabitant of Mars and are
  observing the Earth. At what location in Earths
  orbit would its angular size be largest?
• Inferior conjunction
• Superior conjunction
• Opposition
• Greatest elongation
• Least elongation

Answer A
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• An observer sees the Moon setting at 3am. What
  phase is it?
• Full
• New
• Waxing crescent
• Waning crescent
• Waxing gibbous

Answer E
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• An observer notices a star just rising at 800pm.
  One week later (7 days) she sees the same star
  rise at approximately
• 800pm
• 756pm
• 828pm
• 732pm
• 753pm

Answer D
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• An observer on the Antarctic circle (67.5? S
  latitude) sees the Sun on the horizon at
  midnight. What date is it?
• 21 June
• 21 September
• 21 March
• 21 December
• This is impossible.

Answer D
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• Which of the following is not a scientific
  hypothesis?
• Elvis is alive.
• The Moon has frozen water at the bottom of deep
  craters.
• The Earth is 4,600 yrs old.
• Dogs have souls.
• Plutos orbit is a parabola.

Answer D
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• Retrograde motion is seen for
• All planets
• Only planets closer to the Sun than Earth
• Only planets farther from the Sun than Earth
• Only Mars
• Never actually seen This is a myth that Kepler
  disproved

Answer A
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• Suppose a new planet were discovered at a
  distance of 100 AU from the Sun. Use Keplers 3rd
  law to determine its orbital period.
• 10 yr
• 33 yr
• 100 yr
• 150 yr
• 1,000 yr

Answer E
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• When Venus is closest to the Earth, which is not
  true?
• It is in orbit around the Sun
• It is at inferior conjunction
• It is at opposition
• Is it in the ecliptic
• It is in a line with the Sun and Earth

Answer C
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• Kepler determined that planetary orbits have
  which geometric form?
• Circles
• Hyperbola
• Ellipse
• Rhomboid
• Parabola

Answer C
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• If Eratosthanes had measured a vertical pole
  shadow angle of 15 instead of 7.5 in Alexandria
  on the same day that the sun was at the zenith in
  Syene, how would that have affected his estimate
  for the Earths size?
• The Earths size would have been 2x as large
• The Earths size would have been 4x as large
• The Earths size would have been 2x smaller
• The Earths size would have been 4x smaller
• The Earths size would have not have changed
  this measurement depends on eclipse shadows

Answer C
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• As viewed from Earth, which planet can never be
  seen at opposition?
• Mars
• Jupiter
• Pluto
• Venus
• Saturn

Answer D
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• An observer at the equator looking at the zenith
  is viewing
• The South celestial pole
• A point on the Celestial equator
• The South celestial nadir
• First point of Aries
• The star Polaris

Answer B