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Transcript
Welcome to Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the monthOctober 5, 2010 Dr. Uwe Trittmann Today’s Topics • Close Encounter with Jupiter • The Night Sky in October Observing Planets • Inner Planets: closer to sun than Earth – Mercury & Venus – Always close to sun in the sky • Outer Planets: further from sun than Earth – Mars, Jupiter, Saturn, Uranus, Neptune, Pluto – Best viewing when opposite of sun in the sky Inner Planets superior conjunction Inner planet eastern elongation western elongation inferior conjunction Earth Outer Planets quadrature conjunction Earth quadrature Outer planet opposition Close Outer Planet (Mars) Size of planet varies a lot as Earth moves Earth Outer planet Far-Out Planet (e.g. Jupiter) Earth Size of planet varies little as Earth moves Outer planet Jupiter • • • • Color: yellowish-white Brightness: up to –2.9m Size: up to 50” When to observe: most of the year, except for some months around conjunction • Difficulty: easy, moons visible in binoculars Jupiter & Moons General Features of Jupiter • Largest planet • Low density – Primarily ball of light gases compressed by gravity • • • • • Fastest rotation No seasons Has Rings 63 Moons 1/1000 mass of sun, 320x Earth Jupiter’s Orbit • Average distance from Sun: 779 mill. km = 5.2 A.U. • Eccentricity: 0.0488 • Closest to Sun: 741 mill. km • Farthest from Sun: 817 mill. km • Jupiter Year = 11.86 Earth years Kepler’s First Law The orbits of the planets are ellipses, with the Sun at one focus Ellipses a = “semimajor axis”; e = “eccentricity” Kepler’s Second Law An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal times Kepler’s Third Law The square of a planet’s orbital period is proportional to the cube of its orbital semi-major axis: P 2 a3 a P Planet Orbital Semi-Major Axis Orbital Period Mercury 0.387 0.241 Venus 0.723 0.615 Earth 1.000 1.000 Mars 1.524 1.881 Jupiter 5.203 11.86 Saturn 9.539 29.46 Uranus 19.19 84.01 Neptune 30.06 164.8 Pluto 39.53 248.6 (A.U.) (Earth years) Eccentricity 0.206 0.007 0.017 0.093 0.048 0.056 0.046 0.010 0.248 P2/a3 1.002 1.001 1.000 1.000 0.999 1.000 0.999 1.000 1.001 Jupiter Opposition 2010 • Best since 1951, until 2022 • Distance: 3.9539 AU • unexpected disappearance of Jupiter's South Equatorial Belt (SEB) earlier this year • SEB’s return is often impressive, with dramatic storms erupting suddenly. • Days or years before Jupiter looks normal again Jupiter’s Atmosphere • Cloud bands parallel to equator • Great Red Spot – First observed in 1664 by Robert Hooke Jupiter’s Atmosphere • 86% Hydrogen, 14% Helium; some methane, water, ammonia • Several layers of clouds: ammonia, ammonium hydrosulfide, water • Colors mostly due to compounds of sulfur and phosphorus Great Red Spot • About twice the diameter of the Earth • A hurricane that is hundreds of years old! GRS • As seen by Voyager 1, 1979 Jupiters’ Bands: Zones and Belts • Belts: cool, dark, sinking • Zones: warm, bright, rising • Jovian weather mostly circles the planet due to high rotation rate • Bands exhibit east–west flow Great Red Spot lies between regions of opposite wind flow Naming of Belts & Zones • Tropical, equatorial, temperate Zone/Belt Jupiter Changes Missing Belt! Rotation • About 9 hours for Jupiter and Saturn • Differential rotation: rotation speed varies from point to point on the “surfaces” – Gaseous bodies with no solid surfaces! – On Jupiter, the equatorial regions rotate 6 minutes slower than polar regions • Flattening of planet! • Tilt of rotation axis: – almost none – no seasons! 4 Galilean Moons + 59 others 4 Moons are Planet Size Jupiter’s Galilean Moons Io • Jupiter’s innermost moon • Size and mass similar to our moon • Zips around Jupiter in just 2 days • The most volcanically active object in the solar system – Heated by tidal friction • Eruptions as high as 200 miles, may last for months Io Europa Europa might have liquid water oceans under the surface Life? Ganymede Largest Moon in the solar system: 5260km diameter Icy surface, dark parts are oldest View through the Telescope Comet Shoemaker-Levy 9 • HST image (1994); Earth added to show scale Comet Shoemaker-Levy 9 Headed for Jupiter… Impact on Jupiter Space Probes • Pioneer – Jupiter and Saturn; early 70's – First man-made object to leave solar system • Voyager – “Grand Tour” of Jupiter, Saturn, Uranus and Neptune – Launched 1977; arrived 1979 • Galileo – Launched in 1989 on space shuttle – Boosted by gravitational assists from Earth and Venus – Two-part spacecraft arrived late 1995 • Atmospheric probe entered Jupiter's atmosphere 12/7/95 • Orbiter the first permanent orbiter of outer planets • Cassini - arrived at Saturn 2004, Huygens probes Titan right now Internal Structure • Gas of increasing density and pressure • On Jupiter and Saturn, conditions are such that hydrogen becomes metallic; dense cores • Uranus and Neptune probably have conducting slushy layers Magnetospheres • Very strong – Jupiter's extends past the orbit of Saturn! • Indicate the presence of conducting cores The Night Sky in October • The sun is past autumn equinox -> longer nights! • Autumn constellations are coming up: Cassiopeia, Pegasus, Perseus, Andromeda, Pisces lots of open star clusters! • Jupiter is visible most of the night Moon Phases • Today (Waning Crescent) • 10 / 7 (New Moon) • 10/ 14 (First Quarter Moon) • 10 / 22 (Full Moon) • 10/ 30 (Last Quarter) Today at Noon Sun at meridian, i.e. exactly south 10 PM Typical observing hour, early October Uranus Neptune Jupiter SouthWest High in the sky: The summer triangle Due North Big Dipper points to the north pole High up – the Autumn Constellations • W of Cassiopeia • Big Square of Pegasus • Andromeda Galaxy Andromeda Galaxy • “PR” Foto • Actual look East Perseus and Auriga with Plejades and the Double Cluster Greek Mythology in the Sky South 2006 • Planets – Uranus – Neptune • Zodiac: – Capricorn – Aquarius South – 2007 • Planets – Uranus – Neptune • Zodiac: – Capricorn – Aquarius South – 2008 • Planets – Uranus – Neptune • Zodiac: – Capricorn – Aquarius South – 2009 • Planets – Uranus – Neptune • Zodiac: – Capricorn – Aquarius South – 2010 • Planets – Uranus – Neptune • Zodiac: – Capricorn – Aquarius Mark your Calendars! • Next Starry Monday: November 1, 2010, 7 pm (this is a Monday • Web pages: – http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.) – http://www.otterbein.edu/dept/PHYS/ (Physics Dept.) )