Astronomy 100 The Solar System Tuesday, Wednesday, Thursday Tom Burbine [email protected] is a galaxy?HW #2Slide 4When we are looking at stars or galaxiesMilky Way GalaxyWhat is the Universe?Slide 8What causes seasons?SeasonsSlide 11SolsticesEquinoxesSlide 14ReasonsMars is now visible in the skyAngular sizeMore precise distancesTerminology for looking at the skyCelestial SphereSlide 21Slide 22What is a constellation?ConstellationsSlide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Ursa MajorWhat are the constellations named afterSlide 35Slide 36Slide 37ZodiacSlide 39Slide 40Slide 41Question:Answer:Slide 44Slide 45Why don’t all the constellations have ancient names?Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Long Term ChangesPrecessionForcesSlide 56Because of precessionModelsSlide 59What did the ancients thinkSlide 61Slide 62Slide 63Slide 64RetrogradeStellar ParallaxSlide 67Ancient astronomers could not detect stellar parallaxPtolemy’s (100-170 AD) Model of the UniverseNicholas Copernicus (1473-1543)Tycho Brahe (1546-1601)Johannes Kepler (1571-1630)Kepler was trying to match an orbit to Tycho’s observations of MarsKepler’s 1st LawSlide 75Eccentricity (e)Slide 77DefinitionsKepler’s 2nd lawSlide 80Kepler’s 3rd LawCalculationsHow long does it take Jupiter to go around the SunAnother exampleThe calculationSlide 86Slide 87Slide 88You can calculate a planet’s orbital speedSlide 90LaboratorySlide 92Any Questions?Astronomy 100The Solar SystemTuesday, Wednesday, ThursdayTom [email protected] is a galaxy?HW #2•Due tomorrow (June 10th)What is a galaxy?•Is a massive, gravitationally bound system consisting of stars, gas and dust, and dark matter. Galaxies can contain between ten million and a trillion stars•Dark matter is matter that does not emit or reflect enough radiation to be seen, but whose gravitation effects can be felthttp://en.wikipedia.org/wiki/Image:NGC_4414_%28NASA-med%29.jpgWhen we are looking at stars or galaxies•We are looking into the pastLight-year is the distance light travels in a year.Milky Way Galaxy•Milky Way is 100,000 light years in diameter•There are ~200 billion stars in the Milky Way (estimates from 100-400 billions stars)http://www.venusproject.com/ecs/images/photos/galaxy.jpgWhat is the Universe?What is the Universe?•Sum total of all matter and energy – all galaxies and everything between them•Observable universe – portion of the universe that can be seen from Earth, probably only tiny portion of the whole universe~93 billion Light-yearswideWhat causes seasons?•The tilt of the Earth’s axis relative to the eclipticSeasonsSolstices•Summer Solstice –June 21 – Northern Hemisphere receives its most direct sunlight•Winter Solstice – December 21 – Northern Hemisphere receives its least direct sunlightEquinoxes•Sun shines equally on both hemispheres•Spring Equinox – March 21 – Northern Hemisphere goes from slightly tipped away from the Sun to slightly tipped towards•Fall Equinox – September 21 - Northern Hemisphere goes from slightly tipped toward from the Sun to slightly tipped awayWhy does the orbital difference not matter?Reasons•There is only a 3% difference in the distance from the Earth to the Sun at its farthest and closest point•The Earth is actually closer to the Sun in the winter than in the summerMars is now visible in the sky•http://www.post-gazette.com/pg/10025/1030378-369.stmAngular size•We measure distances in the sky using angles•180o in the observable skyMore precise distances•1 degree = 60 arcminutes (symbol ´)•1 arcminute = 60 arcseconds (symbol ´´)•So something that is 2 degrees, 10 arcminutes, 22 arcseconds would be written as•2o 10´ 22´´Terminology for looking at the skyCelestial Sphere•an imaginary sphere of infinite extent on which all celestial objects appear to lie•http://www.skyandtelescope.com/s?action=loginCelestial SphereWhat is a constellation?Constellations•People refer to constellations as a pattern of stars•Astronomers refer to constellations as specific regions of the sky•In 1928, the IAU (International Astronomical Union) decided there were 88 constellations•Many of the constellation names go back thousands of yearsConstellations• The constellations are totally imaginary things that poets, farmers and astronomers have made up over the past 6,000 years (and probably even more!). •The real purpose for the constellations is to help us tell which stars are which, nothing more.What is thisconstellation?OrionBigger the star, the brighter it isOrion was the son of the god of the sea, Poseidon and a great hunter.One story is that he made an enemy of Hera who sent a scorpion to sting him.Orion was restored to health by Ophiuchus, the first doctor of medicine. Another story is that Artemis was tricked by by Apollo to shoot an arrow at Orion. When he died, Poseidon asked Zeus to put him among the stars.Ursa Major•Ursa Major, the Great Bear, was identified with a bear by native American Indians of the Northeastern United States and the ancient Greeks. •The name common in Britain, the Plough,seems to have a medieval origin, •Another common name among northern European cultures is the Wain, a shortened form of wagonWhat are the constellations named after•14 men and women•9 birds •2 insects•19 land animals•10 water creatures•2 centaurs•one head of hair •a serpent•a dragon•a flying horse•a river•29 inanimate objects•Originally considered part of Leo’s tail•Named after Queen Berenice II of Egypt, wife of Ptolemy III Euergetes (246 BC - 221 BC)•Around 243 BC, the king undertook a dangerous expedition against the Syrians, who had murdered his sister. •Berenice swore to the goddess Aphrodite to sacrifice her famous long hair if her husband returned safely. •He did, she had her hair cut, and placed it in the goddess' temple.•By the next morning, the hair had disappeared. •To appease the furious king and queen (and save the lives of the temple priests), the court astronomer, Conon, announced that the offering had so pleased the goddess that she had placed it in the sky. •He indicated a cluster of stars that at the time were identified as Leo's tail, but now have been called Berenice's Hair.Zodiac•The zodiac is an imaginary belt in the heavens extending approximately 8 degrees on either side of the Sun's apparent path (the ecliptic), that includes the