The most incomprehensible thing about the Universe is that it is comprehensible at all. - Albert Einstein Wednesday, September 7, 2011 Homework #1: Chapter 1: end of chapter “problems” 1-10, odd-numbered only, due Wednesday, August 31 Labor Day: September 5th Last Day to Drop: September 6 Last Day to Add: September 13 Wednesday, September 7, 2011 Outline I. The Stars A. Constellations B. The Names of the Stars C. The Brightness of Stars D. Magnitude and Intensity II. The Sky as a Dome Overhead A. The Celestial Sphere B. Sky Charts III. Cycles in the Sky A. Diurnal Motion B. Annual Motion: Stars, Sun C. The Seasons D. The Moving Planets Wednesday, September 7, 2011 Constellations In ancient times, constellations only referred to the brightest stars that appeared to form groups. Wednesday, September 7, 2011 Constellations Today, constellations are well-defined regions on the sky, irrespective of the presence or absence of bright stars in those regions. Wednesday, September 7, 2011 Constellations The stars of a constellation only appear to be close to one another. Usually, this is only a projection effect. The stars of a constellation may be located at very different distances from us. Wednesday, September 7, 2011 Constellations Stars are named by a Greek letter (α, β, γ) according to their relative brightness within a given constellation + the possessive form of the name of the constellation: Orion Betelgeuse = α Orionis Betelgeuse Rigel = β Orionis Rigel Wednesday, September 7, 2011 Constellations (6) Some examples of easily recognizable constellations and their brightest stars Wednesday, September 7, 2011 The Celestial Sphere Wednesday, September 7, 2011 The Celestial Sphere Vocabulary: • longitude/latitude • celestial sphere • celestial pole/equator • horizon/zenith • constellation • ecliptic/zodiac • equinox • solstice Wednesday, September 7, 2011 Latitude/Longitude Rotational axis Wednesday, September 7, 2011 Latitude/Longitude Latitude: angle measured in north/south direction zero degrees at equator +90 degrees at north pole -90 degrees at south pole Longitude: angle measured in east/west direction zero degrees at Greenwich, England measured to 180 degrees east and west Wednesday, September 7, 2011 Horizon/Zenith Horizon: defined by plane perpendicular to your body Zenith: the point directly above your head. changes with time!! zenith x Wednesday, September 7, 2011 Celestial Pole/Equator Wednesday, September 7, 2011 Celestial Pole/Equator Celestial Pole: North and South pole projected onto celestial sphere. Celestial Equator: Earth’s equator projected onto celestial sphere. Wednesday, September 7, 2011 Sky Chart • A flattened celestial sphere (usually one hemisphere). • Shows which objects are visible in the sky from a specified place at a specified date and time. Wednesday, September 7, 2011 Group Work 1. Which bright star is very nearly overhead (near zenith) at 9PM on August 15th? Wednesday, September 7, 2011 Group Work 1. Which bright star is very nearly overhead (near zenith) at 9PM on August 15th? 2. Which bright star is rising in the east at 10:30PM on Valentines Day? Wednesday, September 7, 2011 Group Work 1. Which bright star is very nearly overhead (near zenith) at 9PM on August 15th? 2. Which bright star is rising in the east at 10:30PM on Valentines Day? 3. Which constellation will be on the northern horizon at about 1AM tonight? Wednesday, September 7, 2011 Group Work 4. At what time can you see Orion setting in the west on New Year’s Eve? Wednesday, September 7, 2011 Group Work 4. At what time can you see Orion setting in the west on New Year’s Eve? 5. Saturn is currently in the constellation of Virgo. At what time will it be rising today? Wednesday, September 7, 2011 Group Work 4. At what time can you see Orion setting in the west on New Year’s Eve? 5. Saturn is currently in the constellation of Virgo. At what time will it be rising today? 6. Name a star that never rises or sets from our vantage point here in San Jose. Wednesday, September 7, 2011 Distances on the Celestial Sphere The distance between two stars on the celestial sphere can only be given as the difference between the directions in which we see the stars. degrees (o): Full circle = 360o arc minutes (‘): 1o = 60’ arc seconds (“): 1’ = 60” Wednesday, September 7, 2011 Celestial Pole • From geographic latitude l (northern hemisphere), you see the celestial north pole l degrees above the northern horizon; Wednesday, September 7, 2011 Celestial Pole • From geographic latitude l (northern hemisphere), you see the celestial north pole l degrees above the northern horizon; l Wednesday, September 7, 2011 Circumpolar Stars Looking north, you will see stars apparently circling counterclockwise around the Celestial North Pole. Wednesday, September 7, 2011 Motion in the Celestial Sphere Daily: Monthly: Yearly: Other: Wednesday, September 7, 2011 Motion in the Celestial Sphere Daily: Objects rise in the East and set in the West. Monthly: Yearly: Other: Wednesday, September 7, 2011 Motion in the Celestial Sphere Daily: Objects rise in the East and set in the West. Monthly: Moon seen at different “phases”. Yearly: Other: Wednesday, September 7, 2011 Motion in the Celestial Sphere Daily: Objects rise in the East and set in the West. Monthly: Moon seen at different “phases”. Yearly: Different constellations visible at different times of year. Other: Wednesday, September 7, 2011 Diurnal Motion Picture taken of Earth/Moon from 6.2 million km away on December 16, 1992, by Galileo spacecraft on its way to Jupiter. Wednesday, September 7, 2011 Diurnal Motion Wednesday, September 7, 2011 Diurnal Motion Earth’s rotation is causing the day/night cycle. Wednesday, September 7, 2011 Diurnal Motion The division between daylight and darkness is at the right side of this image of the Earth. How do you know this is the sunset line and not the sunrise line? Wednesday, September 7, 2011 Diurnal Motion If you could hover over the Earth’s north rotational pole and look down at the Earth as it spins, you would see that the Earth spins in a ____________ direction. a) clockwise b) counter-clockwise Wednesday, September 7, 2011 When I heard the learn’d astronomer, When the proofs, the figures, were ranged in columns before me, When I was shown the charts and diagrams, to add, divide, and measure them, When I sitting heard the astronomer where he lectured with much applause in the lecture room, How soon unaccountable I became tired and sick, Till rising and gliding out I wander’d off by myself, In the mystical moist night air, and from time to time, Look’d up in perfect silence at the stars. - Walt Whitman Wednesday, September 7, 2011.