1. Astronomy Picture of the Day

2. Review Question Which of the following provides the most useful
information about the Earth's interior?
A) drilling
B) laser-ranging
C) x-rays
D) seismic waves

3. Review Question
The _____ theory of lunar formation best accounts for the observed similarities and differences between the Earth and the Moon.
A) fission
B) coformation
C) capture
D) impact

4. Review Question Which planet has a surface similar to Earth's Moon
and has no appreciable atmosphere?
A) Mercury
B) Venus
C) Mars
D) Jupiter

6. Question
Jupiter and Saturn were known to the ancient astronomers. Uranus, barely visible to the naked eye, was discovered in 1781.
Neptune is not visible to the naked eye. How was it discovered?

7. Discovery of Neptune
Neptune predicted to exist because of irregularities in Uranus' orbit.
Discovered in 1845 by Johann Galle.
Kepler’s and Newton’s laws in action!
Nice example of how the scientific method works!

8. Gravitational “Slingshots”
Voyager 2 passed by ALL of the Jovian planets during its flight. To do so, it made use of “gravity assists”.
How can a satellite “borrow” energy from a planet that is orbiting the Sun?

9. Gravity Assists Satellite “borrows” energy from orbiting planet
Conservation of energy and Newton’s third law

10. Gravity Assists (cont.)
Precalculated before satellite is launched
Also shows how gravity can eject “Planetesimals” from early solar system

12. Question Zones and belts are, respectively, high and low
pressure systems on Jupiter.
What process would you expect to be taking place
between such regions?
Why do the zones and belts stretch all the way
around Jupiter?

14. Banded structure on other Jovian planets is present, but not as distinct due to more uniform cloud coverage.
Saturn
Neptune
Uranus: bands obscured by haze in stratosphere

15. Storms on Jovian Planets
Jupiter's Great Red Spot: A hurricane twice the size of Earth. Has persisted for at least 300 years.

16. Neptune's Great Dark Spot: Discovered by Voyager 2 in 1989
Neptune's Great Dark Spot: Discovered by Voyager 2 in About the size of the Earth.
Why do storms on Jovian planets last so long?

17. Other Rotational Effects
Is the rotational bulge of the Jovian planets more or less pronounced than that of the terrestrials? Why?

18. Rapid rotation causes Jupiter and Saturn to bulge:
Gravity
Gravity
without rotation
with rotation
Jupiter and Saturn rotate once every ~10 hours. Radius at equator several % larger due to gaseous-liquid composition of the Jovians.
The Jovians are not solid bodies. What other effect does this have on their rotations?

19. Differential Rotation
Rotation period is shorter closer to the equator:
Near poles
At equator
Jupiter
Saturn
Uranus
9h 56m
10h 40m
16h 30m
9h 50m
10h 14m
14h 12m
How do we know?

20. Differential Rotation
Rotation period is shorter closer to the equator:
Near poles
At equator
Jupiter
Saturn
Uranus
9h 56m
10h 40m
16h 30m
9h 50m
10h 14m
14h 12m
How do we know? Tracking storms at various latitudes, or using Spectroscopy and Doppler shift.

21. Differential Rotation
Density of Jovians increases with depth
Rapid “core” rotation
Frictional dragging of outer atmosphere. Most efficient at equator, least at poles.

22. Question
Uranus' axis of rotation lies almost in the plane of its orbit! What effect does this have on the Uranian seasons?

23. Uranus' rotation axis is tilted by 98o
Why? Unknown. Perhaps an early, grazing collision with another large body.
Most extreme seasons of any planet!
Polar regions - alternately light and dark for 42 years