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Uranus in the Sky

Uranus in the Sky. Uranus. As seen by Voyager. Uranus Highlights. Accidently discovered in March 1781 by William Herschel Fits Bode ’ s Law! Visited by Voyager 2 in 1986 Suspicious lack of internal heat – probably leads to bland appearance of atmosphere Composition: ~75% H, ~25% he

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Uranus in the Sky

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  1. Uranus in the Sky

  2. Uranus As seen by Voyager

  3. Uranus Highlights • Accidently discovered in March 1781 by William Herschel • Fits Bode’s Law! • Visited by Voyager 2 in 1986 • Suspicious lack of internal heat – probably leads to bland appearance of atmosphere • Composition: ~75% H, ~25% he • Probably a small rocky core (3% of total mass) • Ice-rock “slush” interior • Bluish color derives from methane which is a good absorber of red light

  4. Discovery of Uranus William Herschel at left discovered Uranus by accident. He used the 6-inch telescope at right, which he built himself.

  5. Featureless Planet

  6. Atmosphere of Uranus

  7. Interior View of Uranus and Neptune

  8. Oddball Properties of Uranus • Magnetic field: • About same Earth’s field • BUT, dipole inclined by 60o and offset from planet center by 1/3 of RU Caught during a field reversal??? • Tilt: • Extreme tilt remains unexplained • Each pole spends 42 years in light and then 42 in darkness

  9. The Odd Magnetic Field of Uranus

  10. Rings of Uranus • Discovered March 1977 during a stellar occultation • Nine narrow rings ranging in width 10-100 km • Thin and faint with particles of size cm to several meters • Dust fills inter-ring gaps • Requires replenishment • Moons Cordelia and Ophelia act to shepherd some rings

  11. Ring Discovery from Occultation

  12. Uranus Ring System

  13. The IR View

  14. Share Question Seasons on Uranus are a) as long as Uranus' year b) non-existent c) one fourth of Uranus' year, or about 20 Earth years long d) four times Uranus' year, or about 320 Earth years long

  15. Discovery of Neptune • By 1821, the orbit of Uranus clearly deviated from its predicted path which couldn’t be explained by influence of known planets. • Evidence for another planet! • “Discovered” by Adams (English, late 1845) and Leverrier (France, 1846) independently • 1st observed by Galle (German) on 9/23/1846

  16. Neptune

  17. Scale of Neptune

  18. Voyager at Neptune

  19. Neptune with Moons

  20. Neptune’s Atmosphere • Belts • Zones • Clouds • Wind - 2200kph at the equator • Storms - ovals and Great Dark Spot • Great Dark Spot: • High pressure region in S. hemisphere, about size of Earth • By 1994, Spot had disappeared, and a new Dark Spot had formed at N. latitudes (HST)

  21. Multi-Wavelength Neptune

  22. Neptune’s Great Dark Spot

  23. Neptunian Weather

  24. Neptune’s Magnetic Field • Surface field similar to Earth’s in strength • Magnetic axis tilted by 47o • Dipole offset by 1/2 RN Unlikely that both Uranus and Neptune are undergoing field reversals at the same time!

  25. Summary of Magnetic Fields

  26. Internal Energy of Neptune • Uranus lacks convection and therefore storms • Neptune does have internal heat like Jupiter and Saturn (Neptune emits 60% more than absorbs) • A MYSTERY! How can Uranus and Neptune be so different when so similar in size and mass? [Inhibition of convection in Uranus?]

  27. Rings of Neptune Voyager 2 found rings, although there had been previous evidence for them • Dark and faint • Little intergap dust • Rings likely composed of dust themselves • Bright arcs in out ring (effect of shepherding?)

  28. Rings of Neptune

  29. Schematic of Neptune’s Rings

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