Solar System Planets: Venus

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Solar System Planets Venus
I. Venus - Basic Facts - Observing Venus -
Orbit and Rotation - Exploration - Thick Cloud
Cover
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• Fast Facts on Venus
• distance 0.723 AU (average)
• as close as 0.718 AU, as far as 0.728 AU
• eccentricity of orbit 0.007
• diameter 12,401 km (0.95 Earth)
• mass 4.9 x 1024 kg 0.815 Earth
• average density 5243 kg/m3
• orbital period 225 days
• rotation period (axis) 243 days
• average temperature 623 K (662 F)
• albedo 0.59 (59 get reflected)
• thick cloud atmosphere

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Venus is at times the brightest object in the
Night Sky

• 16x brighter than the brightest star!!
• - Venus is relatively large, compared to inner
  planets (Mercury, Mars, Moon)
• - Venuss thick clouds reflect 59 of the
  sunlight that hits it (albedo) making it bright
• - Venus is close (so it is bright from Earth)
• - Venus is close to the Sun, so the sunlight
  reaching Venus is brighter than that reaching
  Earth
• Visible for only 3 hours before sunrise and 3
  hours after sunset

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Similar to Mercury, Venus can be seen at greatest
elongations

• Venus visible
• Eastern sky before
• sunrise for several
• months before GWE
• Western sky after
• Sunset for several
• Months after GEE
• next visible times
• GWE 17 August 2004
• GEE 29 March 2004

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• From Earths perspective,
• Venus goes through
• phases like the Moon
• First noticed and
• explained by Galileo
• ? HELIOCENTRIC

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• Solar Transits of Venus
• Next solar transit of Venus June 6th 2012
• Last solar transit of Venus 1874 and 1882
• Very rare b/c Venus orbital plane, Earths
  orbital plane ecliptic have to be aligned
• in order to put Venus against the Sun from our
  perspective (Venus eclipse)

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The bluriness of Venus during its phases
indicates that it has an atmosphere - sunlight
scatters off the atmosphere of Venus as it
passes through - observed as early as the late
1800s! - photograph of Venus taken at inferior
conjunction - surface of Venus will never be
able to be observed in visible photographs
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Venus has peculiar rotation properties - Venus
rotates very SLOWLY on its axis 243 days -
Venus rotates BACKWARDS on its axis compared to
the other planets (retrograde rotation
compared with retrograde motion) - an observer
on Venus would see the Sun rise in the West, set
in the East
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Microwaves used as radar can reveal rotation
info. - rotation speed of Venus - rotation
direction of Venus Microwaves have long enough
wavelengths to penetrate thick clouds
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Radar exploration of Venus started in the 1960s
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Why is Venus retrograde rotation important?

• rotation, orbital revoluation direction is same
  for almost all the planets
• exceptions are VENUS, NEPTUNE, PLUTO
• tells us how the debris disk formed planets
  around the proto-Sun
• one possibility impact of huge planetesimal
  knocked planet into retrograde rotation

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Venus is covered with thick, hot clouds!

• Surface T700 K (850 F)
• If no atmosphere, T115 F
• H20 and CO2 trap IR
• re-radiated light from a planets
• surface Greenhouse Effect
• 1932 absorption lines of
• CO2 in spectrum of Venus
• Venus subject to more intense
• sunlight because it is closer to Sun
• high albedo means at least
• half of sunlight is reflected back
• surface temperatures hot enough
• to boil, evaporate away liquid water

? debate over whether Venus was a hot, dry or
cool, wet world!!
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• Mariner 2 and 5 1962-63, 1967
• flybys in 1962-63 1965
• Venus surface T 800 F
• Venus atmosphere 90-95 CO2
• and no presence of water vapor
• ? runaway greenhouse effect!!
• Venus magnetic field
• Mariner 10 (1973-75)
• flyby en route to Mercury using gravity assist
  to get to Venus
• first spacecraft to have an imaging system
• observed circulation in Venus atmosphere

Mariner 2 spacecraft in 1962
Venus from Mariner 10 in 1975
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Further Spacecraft Exploration of Venus Venera 4
16 set of spacecraft designed by former Soviet
Union astronomers orbiters, landers
(!), probes to study Venus during 1967-1984
first to land on the surface of Venus atm.
pressure 100 x Earth radar
instruments to map the surface of Venus (l 8
cm) sent back first images of surface
before being crushed by atmosphere
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Further Spacecraft Exploration of Venus
Galileo en route to Jupiter, took an orbital
path flyby of Venus in 1990 Magellan
NASAs Venus Orbiter extensive radar systems for
surface studies Launch of Shuttle in May 1989
Plunged into thick atmosphere in 1994
Radar Map of Venus
Magellan deployed from Shuttle