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Introduction to Astronomy ! AST0111-3 (Astronomía) ! ! ! ! ! ! ! ! ! ! ! ! Semester 2014B Prof

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Introduction to Astronomy ! AST0111-3 (Astronomía) ! ! ! ! ! ! ! ! ! ! ! ! Semester 2014B Prof Introduction to Astronomy ! AST0111-3 (Astronomía) ! ! ! ! ! ! ! ! ! ! ! ! Semester 2014B Prof. Thomas H. Puzia Theme Our Sky 1. Celestial Sphere 2. Diurnal Movement 3. Annual Movement 4. Lunar Movement 5. The Seasons 6. Eclipses Precession • The axis of the Earth (and of the celestial sphere) precesses like the axis of rotation of a top (trompo). The period of this movement is very long: P = 26000 yr. • The Earth is not perfectly spherical, it is wider at the Equator by ~43 km. The inclination of the rotational axis and the asymmetric gravitational pull of the Sun and the Moon produce a change (“torque”) in the axis direction. • Thus the Earth's equatorial plane changes position gradually. This precession of the equinoxes was discovered by Hipparchus in the second century BC. • Example: Today, the spring equinox is in Pisces, but in the year 2600 it will be in Aquarius. • Nutation: a small oscillatory motion superimposed on the Earth's axis precession. The Nutation of Equinoxes Nutation (discovered by James Bradley in 1748) is generally described as the sum of higher-order terms of Earth’s polar motion due to some time-variable nature of !tidal forces that act on Earth’s body (“Precise Geoid”). Nutation is generally: split into vector terms parallel and perpendicular to the direction of precession split into short- and long-period terms due to various effects, such as time-dependent distances of moon, sun, jupiter et al., variable tilt of orbits e.g. moon vs. earth orbit, ocean currents, location of Earth crust relative to her NiFe core, etc. largest nutation component (17x9 arcsec) has a period 6798 days or 18.6 years, while the second- largest (1.3x0.6 arcsec) has a period of 183 days. For unknown reasons nutation terms appear to avoid periods in the range of 34.8 to 91 days. Sun View of Earth from Mars Mean distance: 385000 km Mass ratio: 81:1 ! Double planet? No: Barycenter is 1750 km under Earth’s surface Lunar Movement ! We observe that the Moon also changes position with respect to the “fixed” background stars. " This is the result of the Moon’s orbit around the Earth. ! Additionally, we observe that the Moon has phases: new(nueva), 1st quarter (creciente), full (llena), 3rd quarter (menguante). " This is the result of the relative position of the Sun, which illuminates the Moon, as seen from the Earth. ! The Moon always shows the same “face” to the Earth: thus its period of rotation = its period of revolution. " This is a result of the tidal forces (of the sea) between the Earth and the Moon. Note: this does not mean that the opposite “face” of the Moon is always dark (just that we cannot see it). Phases of the Moon Phases of the Moon ! Sidereal month = 27.3d is the time that takes the Moon to orbit once around the Earth. ! Sinodic Month = 29.5d is time it takes lunar phases to repeat themselves Eclipses ! The plane of the lunar orbit is inclined ~5 degrees with respect to the ecliptic plane Eclipses Eclipses of the Moon ! Eclipses of the Moon are more frequent that those of the Sun ! Additionally, the time duration is longer than those of the Sun ! This demonstrates that the Earth > Moon in size. Eclipses of the Sun ! Depending on the type of occultation, eclipses of the Sun can be total, partial, or annular. Eclipses of the Sun ! Depending on the type of occultation, eclipses of the Sun can be total, partial, or annular. Eclipse of the Sun ! Solar Eclipse: as seen from the Earth and the Moon. simulation! 15 Eclipses Solares Solar Eclipses Saros Cycle every ~18 yrs eclipse geometry repeats (but not same as viewed from Earth) Solar Eclipses Saros Cycle every ~18 yrs eclipse geometry repeats (but not same as viewed from Earth) Moon Affects Tides Caused by slight differential gravitational forces on near and far side of Earth facing the Moon. ! Daily effect relatively small: 0.1% change in gravity force between near and far sides. ! During course of 1 day, “effective” net force Earth rotates through 2 high and 2 low tides. ! Compare height of typical high/low tides to pole and equator radius difference due to rotation. Sun Also Affect Tides “Spring” strong “Neap” weak The Sun also produces tides (~5x weaker than Moon). These can add or cancel with those of the Moon. Why does the Moon look dramatically larger sometimes and smaller others? A. In its orbit around the Earth, it occasionally gets really close or really far B. It expands and contracts due to tidal forces C. The atmosphere acts as a magnifying glass so it is bigger sometimes D. It is an optical illusion Why does the Moon look dramatically larger sometimes and smaller others? A. In its orbit around the Earth, it occasionally gets really close or really far B. It expands and contracts due to tidal forces C. The atmosphere acts as a magnifying glass so it is bigger sometimes D. It is an optical illusion Can the Moon’s distance change much in 6 hrs? “Movements” of the Moon Moon distance varies +/- 5% from apogee to perigee over ~7 yrs ➠ ~20% gravitational force variation (causes perigean tides) “Movements” of the Moon Key Concepts: Celestial Sphere + coordinates (more later) Times (days, months, years). Sidereal vs. Solar/Synodic (more later) Seasons. Phases of the Moon. Eclipses. Tides. Theme Coordinate Systems Different types How to use Coordinate Systems Coordinate System Fundamental Poles Coordinates Zero Point Plane Geographic (Earth) Equator Poles latitude Greenwich, UK longitude Local = Horizontal Horizon zenith/nadir elevation (or altitude) Your meridian (also Alt/Az or Az/El) azimuth Equatorial celestial equator celestial poles declination Vernal Equinox right ascension/hour angle Epoch (J2000) Ecliptic ecliptic ecliptic poles ecliptic latitude Sun + VE ecliptic longitude Epoch (J2000) Galactic galactic plane galactic poles galactic latitude Galactic Center galactic longitude Supergalactic supergalactic supergalactic supergalactic latitude Intersection of Galaxy plane and plane poles supergalactic longitude supercluster plane Coordinate Systems Coordinate System Fundamental Poles Coordinates Zero Point Plane Geographic (Earth) Equator Poles latitude Greenwich, UK longitude Local = Horizontal Horizon zenith/nadir elevation (or altitude) Your meridian (also Alt/Az or Az/El) azimuth Equatorial celestial equator celestial poles declination Vernal Equinox right ascension/hour angle Epoch (J2000) Ecliptic ecliptic ecliptic poles ecliptic latitude Sun + VE ecliptic longitude Epoch (J2000) Galactic galactic plane galactic poles galactic latitude Galactic Center galactic longitude Supergalactic supergalactic supergalactic supergalactic latitude Intersection of Galaxy plane and plane poles supergalactic longitude supercluster plane Coordinate Systems Coordinate System Fundamental Poles Coordinates Zero Point Plane Geographic (Earth) Equator Poles latitude Greenwich, UK longitude Local = Horizontal Horizon zenith/nadir elevation (or altitude) Your meridian (also Alt/Az or Az/El) azimuth Equatorial celestial equator celestial poles declination Vernal Equinox right ascension/hour angle Epoch (J2000) Ecliptic ecliptic ecliptic poles ecliptic latitude Sun + VE ecliptic longitude Epoch (J2000) Galactic galactic plane galactic poles galactic latitude Galactic Center galactic longitude Supergalactic supergalactic supergalactic supergalactic latitude Intersection of Galaxy plane and plane poles supergalactic longitude supercluster plane Coordinate Systems Coordinate System Fundamental Poles Coordinates Zero Point Plane Geographic (Earth) Equator Poles latitude Greenwich, UK longitude Local = Horizontal Horizon zenith/nadir elevation (or altitude) Your meridian (also Alt/Az or Az/El) azimuth Equatorial celestial equator celestial poles declination Vernal Equinox right ascension/hour angle Epoch (J2000) Ecliptic ecliptic ecliptic poles ecliptic latitude Sun + VE ecliptic longitude Epoch (J2000) Galactic galactic plane galactic poles galactic latitude Galactic Center galactic longitude Supergalactic supergalactic supergalactic supergalactic latitude Intersection of Galaxy plane and plane poles supergalactic longitude supercluster plane Coordinate Systems Coordinate Systems Equatorial Coordinates R.A. = right ascension! Dec. = declination Coordinate Systems Galactic Horizontal Equatorial Equatorial Coordinates The arc of C-Υ-R-D is the curve of the of Celestial Equator R-S corresponds to a segment of the great meridian circle N-Z-R-S Υ is the vernal equinox or “first point of constellation Aries” (actually in Pisces now). The direction of Υ is nominally “fixed” relative to the stars (but precesses slowly). ! X position of the star: arc between X-C is star’s declination δ (+90°,-90°) arc between Υ-C is star’s right ascension α (0-24h) α increases to the East of Υ. Y Motion! ! of X Motion! of Y Hour angle, H, time since the object X crosses the meridian. Υ D R δ H Equator ! α C If H = 0, object on the meridian (N-Z-R-S), transit, ⇒ ST = α (object passes meridian) East Horizon S West With respect to object X, object Y will Y Motion! of X Motion! A. Transit before object X. of Y X B. Transit after object X. D Υ R C. Transit at the same time. δ H Equator α D. None of the above C East S West Horizon A. Appear to move faster on the sky B. Appear to move slower on the sky C. Appear to move at the same speed D. None of the above, since stars do not move What are the highest/lowest declinations which are visible from Santiago? Locations of visible planets 0h 1h 2h 3h 4h 5h 6h 7h 8h 9h 10h 11h 12h 13h 14h 15h 16h 17h 18h 19h 20h 21h 22h 23h 24h Declination -60 -40 -20 0 20 40 60 40 20 0 -20 -40 -60 -60 -40 -20 0 20 40 60 40 20 0 -20 -40 -60 0h 1h 2h 3h 4h 5h 6h 7h 8h 9h 10h 11h 12h 13h 14h 15h 16h 17h 18h 19h 20h 21h 22h 23h 24h Right Ascension Check out animation of this at: http://www.physics.sfasu.edu/astro/Planets/planetchart.html Locations of visible planets .
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