1 Lecture 4: Venus (Goddess of love & beauty) • Vital Statistics • Orbit & rotation • Interior • Surface • Atmosphere • Greenhouse effect Historical record • Third brightest object • First record of phases by Galileo in 1610 • Transits observed: 1761, 1769, 1874, 1882, 2004 • Last one June 5-6 2012 – next 11 December 2117) • Transits used to measure AU and detect atmosphere Copernican Ptolemaic Venus - vital statistics Orbital semi-major axis 0.723 AU Orbital period 224.70 days Rotational period 243.019 days (retrograde) Eccentricity of orbit <1% Inclination of rotation axis 177.4º Diameter (at equator) 0.949 d Earth (6052 km) Mass 0.815 M Earth Mean density 5240 kg m -3 (0.95 Earth) Most planets in the Solar System have prograde spin Exceptions: Venus, Uranus (& Pluto). As they formed from a single disk the planets should spin in the same direction. Venus, Uranus (& Pluto) may have been hit early on – this would explain their unusual tilt and slow rotation-rate.
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Lecture 4: Venus
(Goddess of love & beauty)
• Vital Statistics
• Orbit & rotation
• Interior
• Surface
• Atmosphere
• Greenhouse effect
Historical record
• Third brightest object
• First record of phases by
Galileo in 1610
• Transits observed: 1761,
1769, 1874, 1882, 2004
• Last one June 5-6 2012 –
next 11 December 2117)
• Transits used to measure
AU and detect atmosphere
Copernican
Ptolemaic
Venus - vital statistics
Orbital semi-major axis 0.723 AU
Orbital period 224.70 days
Rotational period 243.019 days (retrograde)
Eccentricity of orbit <1%
Inclination of rotation axis 177.4º
Diameter (at equator) 0.949 dEarth (6052 km)
Mass 0.815 MEarth
Mean density 5240 kg m-3 (0.95 Earth)
Most planets in the Solar System have prograde spin
Exceptions: Venus, Uranus (& Pluto). As they formed from
a single disk the planets should spin in the same direction.
Venus, Uranus (& Pluto) may have been hit early on – this
would explain their unusual tilt and slow rotation-rate.
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A Venusian Solar day (noon to noon) is 116.8 Earth days.
This is almost exactly 1/5 its synodic period (583.92d, the
orbital period viewed from Earth). This means Venus
presents nearly the same face to us on closest approach.
Is this near 5:1 resonance
a coincidence?
Yes.
No known way for
Earth to influence
Venus significantly.
Exploration of Venus
• Spectroscopy/imaging from Earth – CO2 found in 1932.
Imaging shows cloud “features”. Surface temp. ~750 K !!
• Radar data dominate, particularly Magellan (1990-94).
• Landers – all Russian. Venera 3 (1965). Crushed!
Venera 9 (1975) sent first picture. Others followed.