DISCOVER THE UNIVERSE
DISCOVER THE UNIVERSE AST 1002
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This 7 page Class Notes was uploaded by Ms. Adrian Buckridge on Friday September 18, 2015. The Class Notes belongs to AST 1002 at University of Florida taught by Jonathan Tan in Fall. Since its upload, it has received 44 views. For similar materials see /class/206973/ast-1002-university-of-florida in Astronomy at University of Florida.
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Date Created: 09/18/15
wesrte im 39asrro ull ed nclimgasIIOOZi index 1mm 2 Optional Discussion sections start Jan 18th see me at end of lecture if you can t make one of these times Tuesday 155pm period 7 Bryant 3 Wednesday 1040am period 4 Bryant 3 Thursday 300pm period 8 Bryant 3 Of ce hr Thursday 5pm Bryant 302 3 Info on Quiz 1 and Homework 1 will be announced in lecture 4 Reading for this week pages l34 of Chaisson amp McMillan then continue reading from p34 onwards gt Chapter 2 to p54 Key Concepts Lecture 2 Scientific Notation Scale of the Solar System amp Universe use of scale factors Light travel time Wave model of light and the electromagnetic spectrum Daily Motion of the Sun and Stars The Celestial Sphere The Solar System our nearest planetary neighborhood iSize ofEarth Radius r 6400 km 64 X 10 X10 X10 64X103km Circumference C 2m 40000km 40X104km iDistance to Moon 384000km 3842105 km iDistance to Sun 150X106km l Astronomical Unit AU iDistance from Sun to Pluto 39 5AU 59X109km iSize of Sun Radius r 700000km 7 X 105km How much bigger is the 7X105km 7 H 7 2 Sun than the Earth 7 764X10 7 764X10 100 Light travel time Speed oflight in vacuum c 300000 kms 3X 105 kms Distance speedxtime ie d c t so d c t Work out how long light takes to cross the above distances Light travel time is proportional to distance t lc x d t a d The Sun is 1 AU away ie 83 light minutes away Pluto is 395X83 light minutes 55 light hours away from the Sun We are always looking back in time this is a fundamental concept FoImula given to you in exams speed distance time Ifthe light travel time from us to star A is 5 years and the light travel time from us to star B is 100 years then 7 A Star B is 10 times closer than star A 7 B Star B is 20 times closer than star A 7 C Star B is the same distance as star A 7 D Star B is 10 times further than star A 7 E Star B is 20 times further than star A 39 LIImun mm Relative sizes of the Sun and Planets Pam v 111 i J Use Appendix 3 Table 3A 2Ain 5th in Chaisson Let s set lAU 1m Withthis scale ofl AU 1m What are the sizes ofthe Bath and Sun How far is it to the nearest star actual distance is about 4 light years The Galaxy and the UniveIse 7 Distance from Sun to nearest star 4 light yea1s ly 4X63000AU 253000 253x105 AU JDistance from Sun to Center ofthe Galaxy 26000ly iDistance to nearby galaxies about 1x106 ly JDistance to fmthest known galaxies about 10x1091y We can not hope to Visit objects outside the solar system in our lifetime The easiest way we can learn about distant objects is by studying the light they emit mation in their light we can measu at Using info re compositions temper ures distances masses and ages of astronomical objects As light travels at a uite speed by looking further and further away we look back further and further into the past One way we can think of light is as a wave of electric and magnetic elds Examples of electric elds Examples of magnetic elds as i Properties of Waves A wave is described by four properties The wavelength 9 units of length The amplitude of the wave The speed of the wave c units of speed lengthtime The frequency of the wave f units of ltime Hertz Three of these properties are interrelated c f X 9 Wavelength Crest IAmplitude Undisturbed Trough state gt Direction of wave motion The Wave Nature of ElectroMagnetic Radiation All EM radiation is composed of two waves that move together 7 An electric eld and a magnetic eld 7 The fields are at 90 degrees a right angle to each other 7 It needs no medium to be transmitted through ie it can travel through a vacuum 7 Energy is carried by the wave Electric held vibration Magnetic field vibrai ion comma mam it At a given point in space the eld amplitudes oscillate as the wave goes by The time of one oscillation is the Period P of the wave The number of periods in one second is the frequency f lP eg 50 oscillations per second is a frequency of 50 Hertz In one period the wave travels one wavelength Thus the speed of the wave is cdistancetime NP 7 f Eiecini Magnum i gt T9 obsewei It is an observed law of nature that the speed of light is constant in a vacuum c constant 3x105kms so higher frequency light has a shorter wavelength and Vice versa Daily Motions of Sun amp Stars Sun 7 rises in the east Waves of different wavelengths and frequencies make up the EM spectrum 7 sets in the west 7 travels on an arc across the sky 7 24 hours Solar day The visible colors are one 7 Due to rotation of the 111 small part of the EM spectrum Equot 7 Wavelengths longer than red are called infrared 7 Wavelengths shorter than the blue are called the ultraviolet IEM spectrum extends from radio to gamma rays Stars Visrble light 1s only a very small 7 stars travel on arcs in part of the EM the sky movmg from spectrum east to west 7 some stars rise and set IThe Earth s transmits certain CIICUanolar frequencies 7 due to rotation of Earth lmlcanJm 1mm 7 23 hours 56 min lnanumeter nm in vm Sidereal Day u can magne a e s ars are attached to the surface of a great sphere The Earth appears to be at the center of the sphere The sphere rotates from east to west on an axis that points to the north celestial pole To explain the daily motions of the sky you can imagine the sphere rotating once in 23 hours 56 minutes But of course these motions are really due to the spinning of the Earth Celestial pole extends from the rotation axis of the Earth all stars appear to rotate about this point some stars are circumpolar some stars rise amp set Celestial equator extends from the Earth s equator Your latitude on Earth determines the angle at Which stars Will rise amp set With respect to your local horizon Discussed in class Note the angle the ar trails make with the horizon 90 degrees You are kidnapped drugged and placedin a ark room for an inde nite period of time You escape and nd a radio to call for help but you don t lmow whereyon are Luckily it s a clear night You watch the stars while and you see the stars rising at a 45 degree angle with respect to your horizon What canyon tell your rescuers about your location
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