Astronomy Picture of the Day

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

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

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

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?

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!

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?

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

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

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?

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

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

Neptune's Great Dark Spot: Discovered by Voyager 2 in 1989 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?

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

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?

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?

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.

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

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

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