* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Test 2 review session
History of astronomy wikipedia , lookup
Tropical year wikipedia , lookup
Observational astronomy wikipedia , lookup
Outer space wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Planets beyond Neptune wikipedia , lookup
Geocentric model wikipedia , lookup
Nebular hypothesis wikipedia , lookup
Directed panspermia wikipedia , lookup
Dwarf planet wikipedia , lookup
Astronomical unit wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Exoplanetology wikipedia , lookup
Astrobiology wikipedia , lookup
Naming of moons wikipedia , lookup
IAU definition of planet wikipedia , lookup
Extraterrestrial skies wikipedia , lookup
Definition of planet wikipedia , lookup
Planetary habitability wikipedia , lookup
Solar System wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Planets in astrology wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Extraterrestrial life wikipedia , lookup
Comparative planetary science wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Review for Test #2 October 27 Topics: • Telescopes • The Solar System and its Formation • The Earth and our Moon • The Terrestrial Planets • The Jovian Planets • Moons, Rings, Pluto, Comets, Asteroids, Dust, etc. Methods • Conceptual Review and Practice Problems Chapters 3 - 8 • Review lectures (on-line) and know answers to clicker & HW questions • Try practice quizzes on-line (in MA) •Bring: • Two Number 2 pencils • Simple calculator (no electronic notes) Reminder: There are NO make-up tests for this class Test #2 Review How to take a multiple choice test 1) Before the Test: • Study hard • Get plenty of rest the night before 2) During the Test: • Draw simple sketches to help visualize problems • Solve numerical problems in the margin • Come up with your answer first, then look for it in the choices • If you can’t find the answer, try process of elimination • If you don’t know the answer, Go on to the next problem and come back to this one later • TAKE YOUR TIME, don’t hurry • If you don’t understand something, ask me. Test #2 Useful Equations Kepler’s laws, including: P2 a3 Gravitation: F= G m1 m2 R2 Equivalence of Matter and Energy: E = mc2 Optical Telescopes - Refracting vs. Reflecting Refracting telescope Focuses light with a lens (like a camera). object (point of light) image at focus Problems: - Lens can only be supported around edge. - "Chromatic aberration". - Some light absorbed in glass (especially UV, infrared). - Air bubbles and imperfections affect image quality. Reflecting telescope Focuses light with a curved mirror. <-- object image - Can make bigger mirrors since they are supported from behind. - No chromatic aberration. - Reflects all radiation with little loss by absorption. Prime focus (GMRT) Offset Cassegrain (VLA) Beam Waveguide (NRO) Reflector TypesCassegrain focus (AT) Naysmith (OVRO) Dual Offset (ATA) Seeing * Air density varies => bends light. No longer parallel Parallel rays enter atmosphere dome No blurring case. Rays brought to same focus. Blurring. Rays not parallel. Can't be brought into focus. CCD * Sharp image on CCD. Blurred image. Interferometry A technique to get improved angular resolution using an array of telescopes. Most common in radio, but also limited optical interferometry. D Consider two dishes with separation D vs. one dish of diameter D. By combining the radio waves from the two dishes, the achieved angular resolution is the same as the large dish. X-ray Optics X rays and gamma rays will not reflect off mirrors as other wavelengths do; need new techniques. X rays will reflect at a very shallow angle, and can therefore be focused. Gamma Rays cannot be focused at all; images are coarse The Structure of the Solar System L3 L5 L4 ~ 5 AU ~ 45 AU Orbits of Planets All orbit in same direction. Most orbit in same plane. Elliptical orbits, but low eccentricity for most, so nearly circular. Two Kinds of “Classical” Planets "Terrestrial" "Jovian" Mercury, Venus, Earth, Mars Jupiter, Saturn, Uranus, Neptune Close to the Sun Small Mostly Rocky High Density (3.3 -5.3 g/cm3) reminder: liquid water is 1 g/cm3 Slow Rotation (1 - 243 days) Few Moons No Rings Main Elements Fe, Si, C, O, N: we learn that from the spectra Far from the Sun Large Mostly Gaseous Low Density (0.7 -1.6 g/cm3) Fast Rotation (0.41 - 0.72 days) Many Moons Rings Main Elements H, He Dwarf Planets compared to Terrestrial Planets "Terrestrial" Dwarf Planets Mercury, Venus, Earth, Mars Pluto, Eris, many others Close to the Sun Small Mostly Rocky High Density (3.3 -5.3 g/cm3) Slow Rotation (1 - 243 days) Few Moons No Rings Main Elements Fe, Si, C, O, N Far from the Sun Very small Rock and Ice Moderate Density (2 - 3 g/cm3) Rotation? Few Moons No Rings Main Elements Fe, Si, C, O, N And an icy surface initial gas and dust nebula dust grains grow by accreting gas, colliding and sticking continued growth of clumps of matter, producing planetesimals planetesimals collide and stick, enhanced by their gravity result is a few large planets Hubble observation of disk around young star with ring structure. Unseen planet sweeping out gap? Terrestrial - Jovian Distinction Terrestrial planets: Inner parts of Solar Nebula hotter (due to forming Sun): mostly gas. Accretion of gas atoms onto dust grains relatively inefficient. Jovian planets: Outer parts cooler: ices form (but still much gas), also ice "mantles" on dust grains => much more solid material for accretion => larger planetesimals => more gravity => even more material. Jovian solid cores ~ 10-15 MEarth . Strong gravity => swept up and retained large gas envelopes. Composition of Terrestrial planets reflects that of initial dust – it is not representative of Solar System, or Milky Way, or Universe. Earth's Internal Structure How do we know? Earthquakes. See later Crust: thin. Much Si and Al (lots of granite). Two-thirds covered by oceans. Mantle is mostly solid, mostly basalt (Fe, Mg, Si). Cracks in mantle allow molten material to rise => volcanoes. Core temperature is 6000 K. Metallic - mostly nickel and iron. Outer core molten, inner core solid. Atmosphere very thin The Greenhouse Effect Main greenhouse gases are H2O and CO2 . If no greenhouse effect, surface would be 40 oC cooler! The Moon QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Tides A feature of oceans (but solid material has small tides too). Two high and two low tides per day. Tides are due to Moon's gravitational pull being stronger on side of Earth closest to it (Sun causes smaller tides). Earth-Moon gravity keeps them orbiting each other. But side of Earth closest to Moon has slightly stronger pull to Moon => bulges towards it. Other side has weaker pull => bulges away compared to rest of Earth. The Earth spins once a day while the bulge always points towards and away from the Moon => high and low tides. Tides Mercury Mass = 3.3 x 1026 g = 0.055 MEarth Radius = 2439 km = 0.38 REarth Density = 5.4 g/cm3 Semimajor axis = 0.39 AU Venus Mass = 0.82 MEarth Radius = 0.95 REarth Density = 5.2 g/cm3 Average distance from Sun = 0.72 AU Orbital period = 225 days Rotation period = 243 days (longer than orbital period, and retrograde!) Mars Mass = 0.11 MEarth Radius = 0.53 REarth Density = 3.9 g/cm3 Average distance from Sun = 1.52 AU eccentricity = 0.093 Range in distance from Sun = 1.38 1.66 AU Rotation Period = 24.6 hours Orbital Period = 687 days Pathfinder site was an outflow channel Red arrows: rounded boulders indicating water erosion? White arrows: "conglomerate" rock, like in Earth's riverbeds? Blue arrows: sharp-edged boulders, volcanic rock? The Jovian Planets (Gas Giants) Jupiter Saturn Uranus Neptune (roughly to scale) Storms on Jovian Planets Jupiter's Great Red Spot: A hurricane twice the size of Earth. Has persisted for at least 340 years. New storm “Oval BA” Neptune's Great Dark Spot: Discovered by Voyager 2 in 1989. But had disappeared by 1994 Hubble observations. About Earth-sized. Why do storms on Jovian planets last so long? On Earth, land masses disrupt otherwise smooth flow patterns. Not a problem on Jovian planets. Storms on Jovian Planets Jupiter's Great Red Spot: A hurricane twice the size of Earth. Has persisted for at least 340 years. New storm “Oval BA” The Galilean Moons of Jupiter (sizes to scale) Io Closest to Jupiter Europa Ganymede Callisto Furthest from Jupiter Radii range from 1570 km (Europa, slightly smaller than our Moon), to 2630 km (Ganymede - largest moon in Solar System). Orbital periods range from 1.77 days (Io) to 16.7 days (Callisto). The closer to Jupiter, the higher the moon density: from 3.5 g/cm3 (Io) to 1.8 g/cm3 (Callisto). Higher density indicates higher rock/ice fraction. Saturn's Rings (all Jovians have ring systems) - Inner radius 60,000 km, outer radius 300,000 km. Thickness ~100 m! - Composition: icy particles, <1 mm to >10m in diameter. Most a few cm. - A few rings and divisions distinguishable from Earth. Oort Cloud is a postulated huge, roughly spherical reservoir of comets surrounding the Solar System. ~108 objects? Ejected planetesimals. A passing star may dislodge Oort cloud objects, plunging them into Solar System, where they become comets. If a Kuiper Belt object's orbit takes it close to, e.g., Neptune, its orbit may be changed and it may plunge towards the inner Solar System and become a comet. Study hard and do well!