1 Where we are in the Universe 2 Motions on the sky Milky Way Galaxy 200 billion stars Galactic year 225 million yr Our sun is 4 6 billion yr old 25 000 light years Or 8 kpc 1 pc 3 26 ly The parallax angle p Small angle formula p in arcsec 1 AU 206265 d 206265 1 AU d p in arcsec Define 1 parsec as a distance to a star whose parallax is 1 arcsec d in parsecs 1 p 1 pc 206265 AU 3 26 ly Milky Way a milky patch of stars that rings the Earth Galactos milk in Greek Galileo found that the Milky Way is made up of stars Galaxy M31 in Andromeda similar to the Milky Way Galaxy 1 Mpc from us Hubble Deep Field 10 day exposure photo Over 1500 galaxies in a spot 1 30 the diameter of the Moon Farthest and oldest objects are 13 billion light years away Hubble Space telescope 100 billion galaxies in the observable Universe 500 Mpc scale What s in the Center The Galactic Center Our view in visible light towards the galactic center GC is heavily obscured by gas and dust Extinction by 30 magnitudes Only 1 out of 1012 optical photons makes its way from the GC towards Earth Galactic center Wide angle optical view of the GC region If one looks at this region with big telescopes and nearinfrared cameras one can see lots of stars If one takes pictures every year it seems that some stars are moving very fast up to 1500 kilometers per second The fastest stars are in the very center the position marked by the radio nucleus Sagittarius A cross Distance between stars is less that 0 01 pc A Black Hole at the Center of Our Galaxy By following the orbits of individual stars near the center of the Milky Way the mass of the central black hole could be determined to 2 6 million solar masses Radio observations with Very Long Baseline Interferometry VLBI that are thousands of times more precise than optical observations good enough to easily pin point a source the size of a pea in New York when sitting in Paris Recent VLBI observations latest issue of Nature Size 1 AU 12 Schwarzschild Radii Density 7x1021 Msun pc3 Will we see a black hole shadow soon 1 Astronomical Unit 1 5 1011 m The Kuiper Belt home for short period comets Starting in 1992 astronomers have become aware of a vast population of small bodies orbiting the sun beyond Neptune There are at least 70 000 trans Neptunians with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune at 30 AU to 50 AU 1 day motion of Varuna Voyagers 1 and 2 Launched in 1977 Voyager 1 is now 95 AU from the Sun 13 light hours or 14 billion km The most distant human made object in the Universe Speed 17 2 km sec 3 6 AU per year Proxima Centauri Alpha Centauri C Closest star 4 2 light years from the Sun It would take 80 000 years for Voyager 1 to reach a neighboring star Plutonium battery will be dead by 2020 Mission may be shut down by 11 2005 Golden record Local Bubble Density 0 05 atoms cm3 Temperature 105 K Remnant of supernova explosion Distance scale 1017 m 107 m 109 m 1011 m 1021 m 3 pc planets Sun 1 AU 10 kpc Solar System distance galaxy between stars Looking through space travel in time 1025 m 100 Mpc Largest structure 1026 m Gpc Hubble radius 1 2 3 Classification of objects on the sky Description of motions of these objects Understanding 1 and 2 The constellations are an ancient heritage handed down for thousands of years as celebrations of great heroes and mythical creatures Here Sagittarius and Scorpius hang above the southern horizon Constellations In ancient times constellations only referred to the brightest stars that appeared to form groups representing mythological figures Constellations 2 Today constellations are well defined regions on the sky irrespective of the presence or absence of bright stars in those regions International Astronomical Union IAU http www iau org IAU Activities nomenclature const html Names and Standard Abbreviations of Constellations The following list of constellation names and abbreviations is in accordance with the resolutions of the International Astronomical Union Trans IAU 1 158 4 221 9 66 and 77 The boundaries of the constellations are listed by E Delporte on behalf of the IAU in Delimitation scientifique des constellations tables et cartes Cambridge University Press 1930 they lie along the meridians of right ascension and paralleIs of declination for the mean equator and equinox of 1875 0 Nominative Genitive Nominative Genitive Andromeda And Andromedae Lacerta Lac Lacertae Antlia Ant Antliae Leo Leo Leonis Apus Aps Apodis Leo Minor LMi Leonis Minoris Aquarius Aqr Aquarii Lepus Lep Leporis Aquila Aql Aquilae Libra Lib Librae 88 constellations Asterisms Small dipper Summer triangle Hipparchus of Rhodes Born 190 BC in Nicaea now Iznik Bithynia now Turkey Died 120 BC in probably Rhodes Greece Catalogue of 850 stars Discovered precession of the Earth s orbit Determined the distance to the moon Compiled trigonometric tables For thousands of years discoveries in math and science were driven by astronomical observations Claudius Ptolemy Born about 85 in Egypt Died about 165 in Alexandria Egypt Almagest A treatise in 13 books Mathematical theory of the motions of the Sun moon and planets Catalogue of 1022 stars and 48 constellations Introduced minutes and seconds Geocentric system Shares with Euclid s Elements the glory of being the scientific text longest in use Original book title is Syntaxis Translated to Arabic as Almagest al majisti and then to Latin That is why stars have Arabic names Venice Petrus Liechtenstein 1515 Star naming business stay away from charlatans OFFICIAL STAR NAMING PROCEDURES Bright stars from first to third magnitude have proper names that have been in use for hundreds of years Most of these names are Arabic Examples are Betelgeuse the bright orange star in the constellation Orion and Dubhe the second magnitude star at the edge of the Big Dipper s cup Ursa Major A few proper star names are not Arabic One is Polaris the second magnitude star at the end of the handle of the Little Dipper Ursa Minor Polaris also carries the popular name the North Star A second system for naming bright stars was introduced in 1603 by J Bayer of Bavaria In his constellation atlas Bayer assigned successive letters of the Greek alphabet to the brighter stars of each constellation Each Bayer designation is the Greek letter with the genitive form of the constellation name Thus Polaris is Alpha Ursae Minoris Occasionally Bayer switched brightness order for serial order in assigning Greek letters An
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