1. Astronomy Picture of the Day

2. 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 (S- & P- waves)‏

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

5. The Jovian Planets Jupiter Saturn Uranus Neptune (roughly to scale)‏ Earth

6. General Characteristics of Jovian Planets: Made up mostly of Hydrogen & Helium Large masses Large Radii Low average densities (Saturn would float!)‏ Strong gravitational fields No solid surface of any kind Short rotation periods Three of Four have significant internal heating How do we get information about these distant giants? Space probes, for example Galileo (video clip)‏

7. 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?

8. 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.

9. 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?

10. Gravity Assists Satellite “borrows” energy from orbiting planet Conservation of energy and Newton’s third law (Demo)‏

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

12. Jupiter's Bands Lighter-colored "zones" and darker-colored "belts". Shadow of a moon Great Red Spot Belt Zone

13. 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. - Convection occurs between zones and belts - Jupiter's rapid rotation stretches bands around the entire planet. - Temperature difference between zones and belts => different chemistry => different coloration.

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

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

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

18. Other Rotational Effects Is the rotational bulge of the Jovian planets more or less pronounced than that of the terrestrials? A) More B) Less

19. Rapid rotation causes Jupiter and Saturn to bulge: Gravity without rotation with rotation Gravity 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?

20. Differential Rotation Jupiter Saturn Uranus Neptune Near poles versusAt equator A bit slower (6 min)‏ Slower (by 26 min)‏ Faster (by about 2 hours)‏ Faster Reflects large-scale wind flows in the planets atmosphere. How do we know? Tracking storms at various latitudes, or using Spectroscopy and Doppler shift.

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

22. Uranus' rotation axis is tilted by 98 o 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