Astronomy 161 -- Autumn 2009 (Prof. Stanek) Final Exam Study Guide (Monday, December 7, 11:30 a.m.) -------------------------------------------------------- There will be 100 questions on the Final Exam. Final will count for 40% of the final grade. Classes to review: The Celestial Sphere Season & Calendar Moon Phases & Eclipses From Ptolemy to Copernicus Tycho, Kepler, & Galileo Newton's Laws Applying Newton's Laws Light Spectra Telescopes Solar System Survey Origin of the Solar System Planets Around Other Stars The Earth Earth's Atmosphere The Moon Mercury Venus Mars Jupiter & Saturn Moons of Jupiter and Saturn Uranus & Neptune Pluto, Eris ... and Beyond Asteroids Comets ------------- Key Concepts: The Celestial Sphere -------------------- (1) The sky as seen from Earth is divided into 88 constellations. (2) It is convenient to pretend the stars are attached to a celestial sphere. (3) The celestial sphere appears to rotate about the celestial poles (1 day). (4) The Sun appears to move west to east relative to stars (1 year). (5) The Moon appears to move west to east relative to stars (1 month). Season & Calendars ------------------- (1) The cause of the seasons is the tilt of the Earth's rotation axis relative to its orbit around the Sun. (2) The day is based on the time between one noon and the next. (3) The year is based on the time between one vernal equinox and the next. (4) The moon (month) is based on the time between one new moon and the next. Moon Phases & Eclipses ----------------------- (1) Lunar phases change as we see more or less of the Moon's sunlit half. (2) The Moon rotates about its axis as it revolves around the Earth. (3) The sidereal month=27.3 days; the synodic month=29.5 days. (4) A lunar eclipse occurs when the Moon passes through the Earth's shadow. (5) A solar eclipse occurs when the Earth passes through the Moon's shadow. From Ptolemy to Copernicus --------------------------- (1) Aristotle (4th cent BC) showed that the Earth is round. (2) Greek astronomers developed a geocentric model for the universe. (3) Ptolemy (2nd cent) used epicycles to explain retrograde motion of planers. (4) Copernicus (16th cent) proposed a heliocentric model for the universe. (5) In the model of Copernicus, retrograde motion is easily explained. Tycho, Kepler, & Galileo ------------------------ (1) Tycho Brahe made accurate measurements of planetary motion. (2) Planetary orbits are ellipses with the Sun at one focus. (3) A line between planet & Sun sweeps out equal areas in equal times. (4) The square of a planet's orbital period is proportional to the cube of its average distance from the Sun. (5) Galileo made telescopic observations supporting the heliocentric model. Newton's Laws -------------- Three Laws of Motion (1) An object remains at rest, or moves in a straight line at constant speed, unless acted on by an outside force. (2) The acceleration of an object is directly proportional to force, and inversely proportional to mass. (3) For every action, there is an equal and opposite reaction. Law of Gravity: (4) The gravitational force between masses M and m, separated by distance r, is F=G(Mm/r^2) Applying Newton's Laws ----------------------- (1) Newton modified and expanded Kepler's Laws of Planetary Motion. (2) Kepler described how planets move; Newton explained why they move. (3) Tides are caused by the difference between the Moon's gravitational force on different sides of the Earth. (4) Tidal forces are slowing the Earth's rotation & enlarging the Moon's orbit. Light ------ (1) Visible light is just one form of electromagnetic radiation. (2) Light can be though of as a wave or as a particle. (3) Light forms a spectrum from short to long wavelengths. (4) A hot, opaque object produces a continuous blackbody spectrum. Spectra -------- (1) A hot, transparent gas produces an emission spectrum. (2) A cool, transparent gas produces an absorption spectrum. (3) Every type of atom, ion, and molecule has a unique spectrum. (4) The most abundant elements in the universe are hydrogen and helium. (5) The radial velocity of an object is found from its Doppler shift. Telescopes ---------- (1) Telescopes use either a lens or a mirror to gather light. (2) The main purposes of a telescope are to gather light and resolve detail. (3) Radio and microwave telescopes use a reflecting dish to focus waves. (4) Telescopes in orbit avoid the distorting effects of the atmosphere. (5) Ultraviolet, X-ray, gamma ray, and most infrared light is visible only from orbit. Solar System Survey -------------------- (1) The terrestrial planets are made primarily of rock and metal. (2) The Jovian planets are made primarily of hydrogen and helium. (3) Moons (a.k.a. satellites) orbit the planets; some moons are large. (4) Asteroids, meteoroids, comets, and Kuiper Belt objects orbit the Sun. (5) Collision between objects in the Solar System cause impact craters. Origin of the Solar System --------------------------- (1) A cloud of gas & dust contracted to form a disk-shaped solar nebula. (2) The solar nebula condensed to form small planetesimals. (3) The planetesimals collided to form larger planets. (4) Radioactive age-dating indicates the Solar System if 4.56 billion years old. Planets Around Other Stars --------------------------- (1) Planets can be detected from the Doppler shift of their parent star. (2) Planets can be detected when they eclipse (or transit) their parent star. (3) About 200 planets have been found around stars other than the Sun. (4) Many planetary systems found so far are very different from the Solar System. The Earth --------- (1) The study of seismic waves tells us about the Earth's interior. (2) The Earth is layered into crust, mantle, inner core, and outer core. (3) The Earth is layered because it underwent differentiation when molten. (4) The lithosphere is broken into plates that move relative to each other. (5) The motion of liquid metal in the outer core produces a magnetic field. Earth's Atmosphere ------------------ (1) The Earth's atmosphere consists mainly of nitrogen (N2) and oxygen (O2). (2) Without life, air would have no O2; without oceans, it would have more CO2. (3) The ozone (O3) layer has been partially destroyed by chlorofluorocarbons. (4) Excess CO2 can cause global warming via the greenhouse effect. The Moon -------- (1) The Moon's surface has both smooth maria and cratered highlands. (2) The surface was shaped by heavy bombardment, followed by lava floods. (3) The Moon has a thick crust but a tiny iron-rich core. (4) The Moon may have been ejected when a protoplanet struck the Earth. Mercury ------- (1) Mercury has a 3-to-2 spin-orbit coupling (not synchronous rotation). (2) Mercury has no permanent atmosphere because it is too hot. (3) Like the Moon, Mercury has cratered highlands and smooth plains. (4) Mercury has an extremely large iron-rich core. Venus ----- (1) The surface of Venus is hidden from us by clouds of sulfuric acid. (2) The atmosphere of Venus is hot because of a runaway greenhouse effect. (3) The surface of Venus shows volcanic activity but no plate tectonics. (4) The interior of Venus is similar to that of the Earth. Mars ---- (1) Mars has a tenuous atmosphere, with little water vapor and few clouds. (2) Mar has large volcanoes and a huge rift valley, but no plate tectonics. (3) Robotic "rovers" have given us a close-up look at Mars. (4) Mars has two small irregular moons, Phobos and Deimos. (5) Life on Mars?? Jupiter & Saturn ---------------- (1) Jupiter and Saturn consist mainly of hydrogen and helium. (2) Jupiter and Saturn have belts and zones of clouds, plus circular storms. (3) Jupiter and Saturn have magnetic fields created in metallic hydrogen. (4) Differences between Jupiter and Saturn are due to Jupiter's higher mass. (5) All Jovian planets have rings. Moons of Jupiter and Saturn --------------------------- The Galilean Moons of Jupiter: (1) Callisto: heavily cratered (2) Ganymede: larger then Mercury (3) Europa: covered with smooth ice (4) Io: volcanically hyperactive The Giant Moon of Saturn: (5) Titan: wrapped in an atmosphere Uranus and Neptune ------------------ (1) Uranus and Neptune are nearly identical in their internal structure. (2) The rotation axis of Uranus is tilted by about 90 degrees, causing extreme seasons. (3) Neptune has surprisingly strong storms, driven by internal heat. (4) Triton, the giant moon of Neptune, is a cold world with nitrogen geysers. Pluto, Eris ... and Beyond -------------------------- (1) Pluto and its moon Charon are icy worlds that resemble Triton. (2) Eris, the troublemaker. (3) The Kuiper belt, beyond Neptune, contains small, icy, Pluto-like objects. (4) The icy Kuiper Belt Objects are leftover planetesimals. (5) The research on the Kuiper Belt continues. Asteroids --------- (1) Asteroids are mostly in the asteroid belt between Mars and Jupiter. (2) Asteroids are strongly influenced by the gravity of Jupiter. (3) Asteroids are made of rock, metal, or a combination of both. (4) Meteorites are usually asteroid fragments that have struck Earth. Comets ------ (1) Comets are "dirty snowballs": ice mixed with dust & carbon compounds. (2) When a comet is close to the Sun, it grows an ion tail and a dust tail. (3) Most comets are in the Kuiper belt or the Oort clod, far from the Sun. (4) A comet or asteroid impact might have caused the extinction of dinosaurs.