Hi,Remember that there is an Observatory Open House this evening—see Syllabus for details. Try to take the shuttle bus—picks up behind Computer and Space Sciences Building across from Cambridge hall. Be sure to sign in for lecture and in telescope building. Bus should come around 7:30.Also remember that Homework #3 is due April 1 in lecture—see page 8 of the syllabus.Have a safe spring break. Show someone something in the sky (like Jupiter) or share something interesting. Mrs. DemingLECTURE SUMMARY (3/18 & 3/20)Latest results from the Galileo orbiter were given. Jupiter and its moons have been studied from this orbiter for 4 years. The outer planets have also been imaged using the Hubble Space Telescope. Pluto has never been visited by a space probe, but the Hubble Space Telescopehas provided the most detailed images so far. Should Pluto be considered a planet or something else?Halley first noticed the periodic nature of comets. The very eccentric orbit of Halley's Comet brings it closer to the Sun than Venus and it swings out farther than Neptune. Most of a comet's time is spent in the cold regions of the Solar System, but as it approaches the Sun, sublimation of ices from the nucleus allows the coma and tail to form. Unlike the gas tail which is pushed out of the Solar System by the solar wind, the small bits of rock and dust from the nucleus continue to orbit the Sun. Meteor showers result as the Earth passes through the dust taildebris from a comet. Asteroids lie mostly between the orbits of Mars and Jupiter, yet some have Earth-crossingorbits. Comets and asteroids may undergo perturbations in their orbits as the Sun passes other stars, as the comets pass each other, or as a comet passes a planet. Periodic comets are replenished in this manner. Recently probes have flown past Halley's comet, and 4 asteroids, if you include Dactyl. The near-Earth asteroid, Eros, was studied during the NEAR mission.It is evident from our observations of impact craters on planets and satellites that collisions have occurred throughout the Solar System and even in Earth's past history. Collisions have occurred in the past on Earth (examples: Meteor Crater and Tunguska Event). It has been proposed that Earth suffered a climate altering collision with an asteroid or possibly a comet nucleus approximately 65 million years ago, which led to the mass extinction that included the dinosaurs. Why do scientists theorize that such an event happened? In 1980 Iridium in surprising amounts was detected in the K/T clay in Italy. (K/T refers to rock deposited approximately 65 million years ago, at the boundary between the Cretaceous Period and the Tertiary Period. Above this region we find no skeletal fossils of dinosaurs. About 75% of the species that existed below in the more ancient rock are absent above the K/T clay.) Upon further investigation, Iridium was detected worldwide in this layer. Iridium is not very abundant in Earth's crust, but more abundant in meteorites. Other evidence associated with impacts has also been detected. The "impact winter" theory has gained support in recent years, especially with the discovery of a suspect crater. Dust thrown into the atmosphere and soot from resulting wildfiresplunged the Earth into an "impact winter" in which the food chain was disrupted. Could it happen again? Based on the number of near Earth asteroids--yes. An event with some climate altering results can be expected once every few million years. A really large devastating impact (like 65 million years ago) can be expected once every 100 million years. Astronomers study light from objects to explore the universe. Electromagnetic radiation (light) was described in terms of wavelength and photon energy. In 1873 Maxwell developed a theory involving oscillating electric and magnetic fields to describe light. A 3 dimensional modelwas used to illustrate this concept. There is much more to this phenomenon than the range which our eyes are sensitive to—the visible. Colors result from tiny wavelength differences. Blue lighthas shorter wavelength and greater photon energy than red light. A prism was used to split light into its component colors—a rainbow. Mrs. Deming demonstrated invisible forms of electromagnetic radiation using a fluorescent screen (ultraviolet radiation) and an infrared detector (well I tried).TERMS: Galileo orbiter, Cassini mission, Hubble Space Telescope, comets, coma, nucleus, tail, meteor showers, perturbation, asteroid, meteor, meteorite, iridium, shocked quartz, Chicxulub, impact winter, mass extinction, electromagnetic radiation, wavelength, photon energy, AngstromQUESTIONS:1. What new information about Jupiter and its satellites has the Galileo mission provided?2. Describe recent images of the jovian planets, satellites, and Pluto made by the Hubble Space Telescope.3. Explain how and why a comet changes as it moves through one complete orbit.4. Why do meteor showers occur annually?5. Describe the appearance of an asteroid based on recent images taken by the Galileo and NEAR missions.6. Where are most asteroids found? Do any come near Earth? Explain. 7. Describe how the orbit of a comet can be changed.8. What evidence supports the "asteroid and dinosaur" mass extinction theory?9. How could an impact by an asteroid lead to a mass extinction on Earth.?10. Be able to discuss electromagnetic radiation in terms of wavelength and photon