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by: Rasheed Lebsack


Rasheed Lebsack
OK State
GPA 3.74

Peter Shull

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Peter Shull
Class Notes
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This 0 page Class Notes was uploaded by Rasheed Lebsack on Sunday November 1, 2015. The Class Notes belongs to ASTR 1014 at Oklahoma State University taught by Peter Shull in Fall. Since its upload, it has received 35 views. For similar materials see /class/232853/astr-1014-oklahoma-state-university in Astronomy at Oklahoma State University.

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Date Created: 11/01/15
Astronomy Sec 3 8312010 33400 PM 31 Terrestrial Globe globe voyageset location Meridians Latin for midday and parallels Latitude NS of Equator and longitude EW of Prime Meridian Directions East is rotational direction Relative directions Measures in degrees arcminutes and arcseconds 1 60 3600 Meridians converge at poles length of 1 degree of longitude shrinks as poles are approached Zenith and nadir Arabic for overhead and opposite of overhead 32 Days and Time Sidereal day 23h 56m time for 360 rotation globe voyager view from sun Apparent solar day Range is 24h 30s time between successive sunrises etc Corrosponds to 360 362 rotation Earth s changing orbital speed and tilted axis cause the variation Mean Solar day 24h 00m average length of the apparent solar day wristwatch time Time Zones About 15 wide make travel convenient Each longitude really has its own apparent solar time 33 Years and Calendars Sidereal year 3652564 days time for one true orbit 360 revolution tropical year 3652422 days time for season repetition 359 986 revolution Gregorian calendar Instituted 1582 to match calendar to the tropical year IE the seasons Rule years have 365 days usually but have 266 days when the year is divisible by 4 AND not divisible by 4000 AND if a century year divisible by 400 Thus average length of year 365 14 14000 3400 3652423 days 34 Metric System and Powers of Ten Metric units and prefixes powers of ten astronomical data book 35 Practice with Big Numbers Keck 10 m telescope 70M 70 x 10 to the 6th new 737 Annual groundbased astronomy budget mainly NASA amp NSF 300 M 2 big movies HST spread over 10 years 15 G 15 x 10to the 9 Number of stars in MWG 100 G 10to the 11th 01 T Federal budgetary data 2 graphs FY 2008 GDP 145 T Budget 30 T Debt 100 T 36 Percentages means 1100 FampE 0 10X 1100 1100 01 30T145T 20 20 Astronomy Sec 4 8312010 33400 PM 41 Law of 72 After n years of growth at given annual rate APR accumulation is o 1 APR100 n times the original amount Example after 5 years with APR 3 the growth factor is 1003 5 103 5 116 Doubling time in years is o T double 0693 72 years 1n 1APR100 APR 42 The celestial Sphere sphere p2 voyager HelpBasic concepts Reality for ancients computational convenience for moderns Stars actually at various distances Features based on Earth s axis Celestial poles Celestial Equator Celestial meridians and parallels Celestial meridians converge at poles These features move relative to the stars over 26000 years due to precession of Earth s axis Voyager demo Basics Prec of the Eq Features based on Earth s orbit voyager cel Sph w ecl Coord Ecliptic ecliptic plane ecliptic poles The Zodiac Stars like Polaris are fixed for our lifetime but not over thousands of years quptians had a different north star 43 Altazimuth Coordinates globe p3 altaz math guide dwg voyager local hor w altaz Coord Specify directions relative to observer on ground depending on observer s position and the time Coordinates are c Altitude alt Angle above below horizon 0 o Azimuth az angle clockwise relative to due North 0 Meanings of N S E W 44 Equatorial Coordinates spere eq voyager local hor w eq coord Specify directions relative to celestial meridians and parallels Therefore are almost timeindependent but precession causes the coordinates to very slowly change Coordinates are c Declination Be or 8 Angle N or S of celestial equator 0 00 00 celestial poles at 90 o Right Ascension AA or a Angle E vernal Equinox Oh00m00s Measures in time units where 360 24 hours Vernal Equinox in sun s celestial meridian on first day of spring in northern hemisphere exactly 12 h of daylight 45 Seasons Flashlight amp globe JP Daylight amounts Season dates USA vs Chile Heating vs sunlight s angle of incidence Combined effect of illumination time angle of incidence and distance from sun Role of atmosphere s thermal inertia 46 Precession falling wheel A spinning wheel s responses to torques twisting forces Earth is a gyro with 26000 year period tabletop example Therefore celestial poles and equatorial coordinates slowly change and seasonal cycle tropical year lt 360 orbital time sidereal year Sidereal year tropical year o 126000 x 3652564 days 20 minutes Astronomy Sec 5 8312010 33400 PM Sections 8182 8485 87 810811 51 Longterm astronomical Influences on Climate Milankovitch hypotheses 1920 Apart from variations in sun s light solar heating depends on ellipticity of Earth s orbit and on inclination and precession of Earth s axis All three vary with time so Earth s climate should also vary Supporting evidence only recently Fig 212 Ellipticity Other planets gravitational tug on Earth parallel to ecliptic plane cause its orbit s ellipticity to vary over 10to the 5 yr Aphelionperihelion distance ratio can be as high as 115 Inclination Other planets tugs on Earth perpendicular to its orbital plane cause the inclination of the axis to oscillate between 22 and 245 over 41000 yr This affects the contrast between seasons 52 Planetary Motions Names and order Planets orbit in the same direction and all orbits are roughly in the ecliptic plane demonstrator Voyager The nakedeye planets their appearance to the eye Special locations conjunction opposition and maximum elongations inner planets only When they re in conjunction with the sun Mercury and Venus 53 Lunar Orbit and Phases Elliptical orbit mean radius 13 light sec inclined 5 to ecliptic plane JP Sidereal period 273 d lunar day also Phase names shapes and causes JPs flashlight amp Moon Synodic period 295 days how long it takes the moon to go around the Earth Riding and setting times of the phases Takes a month for moon to go around the Earth Phases Crescent Waxing Crescent half moon 14 waxing Gibbous full waning Gibbous Third Quarter Waning Crescent Half of the moon is always lit by the Sun 54 Origin of Tides Earth and Moon orbit their center of mass 14 Earth radius below Earth s surface model Moon s tidal force difference in the Moon s gravitational force between any two parts of the Earth Tidal and centrifugal forces distort Earth s oceans and its rocky globe 20 cm into a football shape draw Oceanbottom friction holds ocean s bulge ahead of the EarthMoon axis Water tide doesn t point straight toward the Moon 55 Lunisolar Tides Sun also causes tides on Earth but the effect is half the Moon s Two spring and two neap tides occur per synodic month when lunar and solar tides reinforce or partly cancel each other Spring Tides High tides and Low Tides 56 Astronomical Effects of Tides p15a Regular variations in thickness of tidal sediment layers from 9x 10to the 8 yr ago reveal the year had 481 days of 182 hr and the month lasted 234 present days meaning the Moon was 10 closer Now Moon s orbital radius grows 38 cmyr and Earth days lengthen 0002 seccentury p15b Causes oceanbottom friction and Earth s leading tidal bulge Reasoning layers vary regularly in thickness and composition Annual variations in the layering mark the passage of one year a constant Four neapspring layers mark one month so the number of months per year can be counted The number of layers per month gives the number of days per month So days have been shorter in the past according to layers in ground Sec 6 8312010 33400 PM 61 Eclipse Geometry models 2 JPs 5 inclination of Moon s orbit to ecliptic plane makes eclipses tend to occur in pairs and twice per year Umbral and penumbral shadows draw Umbra area on opposite side of sun on Earth where there is no sunlight triangularamp total shade Penumbral partial shape eclipses occur in pairs half a year apart 62 Lunar Eclipses Moon is covered Earth s umbra 110 DE long and 25 DM wide at lunar distance Total and partial eclipses 2 JPs Our atmosphere prevents a pitchblack moon Partial eclipse sometimes has reddish color 63 Solar Eclipses Sun is covered Moon s umbra 110 Dm long lunar distance Umbral spot at most 270 km across Total partial and annular ringlike eclipses 7 JPs p132 p22 JP Eclipse of Sun by Earth was viewed by Kaguya spacecraft in February 2009 64 Scientific Models Models are geometrical or mathematical representations of reality based on physical law They should capture the essential behavior of phenomena and be detailed enough to explain all measurements past and future Eg a point mass represents a falling body But distance time and our five senses limit out knowledge 65 Patterns Recognized by Ancients Astronomical observations recorded in ancient Egypt Babylonia India and China Thousands of years BC people realized the starry skies were predictable o Egyptian calendar ca 50004000 BC solarlunar calendar of 12 months of 30 days o Stonehenge ca 30001000 BC most famous ancient stone structure 4 JPs Cartoon Demonstrates recognition of solar 66 lunar seasonal agricultural and eclipse patterns Heel stone where the sun rises on the first day of summer 57 3 x 19 cycle of solar eclipses takes 19 years after 3 times they repeat A HalfMillennium of Greek Astronomy 500 BC100 AD Pythagoras 500s BC spherical Earth is center of Universe surrounded by 8 concentric celestial spheres and air sphere Their uniform circular motion produces inaudible music of the spheres Aristotle 300s BC 56 spheres Deduced spherical shape of Earth Nondetection of stellar parallax made him believe Universe is geocentric try Eratosthenes 200s BC Estimates Earth s circumference 10 high JP Aristarchus 200s BC Geometrically determined that Sun is 19x farther than Moon via phase timings and 7x bigger than Earth via total eclipses and observed size of Earth s shadow Correct values are 400x and 109x Concluded Sun is at center of Universe and stars are distant Hipparchus 100s BC Used offcenter circles eccentrics for Sun s and Moon s orbits in his geocentric model to produce observed variations in their orbital speeds sketch Ptolemy 100s AD Devised epicycles deferents and equants to explain retrograde motion of planets an asymmetry Mercury s and Venus s epicycles centered on EarthSun axis JP Sec 7 71 8312010 33400 PM A century of European Astronomy 15401620 Nicolaus Copernicus o 2JPs Reemphasized heliocentric model as simpler and better than geocentric model in De RevolutionibusOrbumCoeestium 1 543 demonstrator Heliocentric model predicted gibbous and crescent phases for Mercury and Venus whereas geocentric one predicted only crescents However predicted planetary positions were not much better only good to within 2 degrees 4 moon diameters FampE 527 Reminder Aristarchus also though Universe was helopcentric Nicholas of Cusa 14001464 cardinal and philosopher wrote that Earth is not center of Universe other celestial bodies are like Earth and all follow noncircular paths Tycho Brahe 0 JP He and his staff observed Sun Moon and planets daily 157696 with best precision yet 17 moon diamtere Described the new star supernova SN 1572 in De Stela Nova 1573 Johannes Kepler 0 JP Succeeded Tycho in 1601 used Tycho s data to discover three laws of planetary motion the first two are in Astronomia Nova 1609 third is in HarmoniceMudi 1619 First Law orbits are ellipses Second Law equal areas radius vector area will always be the same Third Law period P in yrto the 2 semimajor axis A in AUto the 3rd FampE 1207 Galileo Galilei o 4 JPs telescope Professor at Padua and Pisa who began automatic observations with 30 mm telescope in 1609 and reported them in SirereusNuncus 1610 Some demystified the heavens sunspots p35 solar rotation and lunar feature Others supported the heliocentric model Jovian disk and satellites and gibbous Venus 72 Motion Notions 73 Velocity v rate at which position is changing m per s ms Acceleration a rate at which velocity is changing ms per s mssquared beam measure velocity at two different locations you would get a different number Take change in velocity time in which it happened aA velAie Sir Isaac Newton Professor at Cambridge JP who developed theoretical physics by building on his own and others work eg Galilei s and published results in PhiosophiaeNaturais Principia Mathematica 1687 Laws of motion 0 1 A body of mass m stays at rest unless acted on by external force ball stopper FampE 128 releasing string at certain time to make ball go certain direction 0 2 Restatement of 1 F ma a Fm o 3 Law of recoil equal and opposite reactions 0 FampE 805 demo Law of universal gravitation between point masses M1 and M2 separated by distance r G is a constatnt FampE 124 0 FgGm1m2rsquared Newton s grav Const o Theoretically speaking all objects pull towards each other in a matter of time Law of conservation of angular momentum L Example for a planet of mass m orbiting the Sun at distance r with velocity v m x r x v L is constatnt stopper platform Sect 8 8312010 33400 PM 81 Newton and Orbits Newton used his laws of motion to derive and improve Kepler s laws Kelper 1 Planetary orbits are ellipses with the Sun at one focus Newton 1 orbits can also be circles parabolas or hyperbolas and 2 the objects orbit their center of mass JP model Kelper 2 A planet s radius vector sweeps out equal areas in equal time Newton same Kepler 3 pA2 AA3 Newton pA2 AA3 1 MPLanet MSun 82 Circular Orbits For an orbit of radius A and period P stopper Orbital velocity is Vcirc 2pieA P Escape velocity is just Vesc squareroot2 Vcirc 14 Vcirc 83 Electromagnetic EM Radiation EM radiation is light EM waves are traveling ripples in the patterns of electrical and magnetic force produced by an accelerating electrical charge a line of electrons would oscillate in response to a passing EM wave Sometimes a particle photon model is better Wavelength and frequency f wave machine Wave speed cf wavelength in a vacuum f and wavelength vary inversely EM spectrum regions 87 Different wavelengths cause different color sensations Atmosphere is a filter that transmits only optical radio and some IR and UV to ground 87 Air turbulence and light pollution degrade observations so high observatories are best p24 p25 p8 4 JPs 84 Optical Telescopes Refractors show Convex objective lens light bends rays to produce image and eyepieces magnify the image beaker laser lens Main defects are chromatic aberration weights expense Reflectors sketch Concave objective mirror at back reflects light rays to produce image concave mirror A secondary mirror reflects image to eyepiece Main defect is spherical aberration Mountings allow telescopes to be smoothly moved to compensate for Earth s rotation Altazimuth mount one axle vertical with motors on both axles Equatorial mount one axle aimed at the celestial pole with motor on that axle only HSMO home page Newest and notable ground telescope designs seek better performance at lower cost Features altazimuth mounts segmented mirrors active optics spin casting liquid mirrors robotic control like OSU s telescope 2 JPs p94 p84 p16 p23 p54 GTC pp2125 p26 11JPs 1789 telescope reflector altazimuth Sec 9 8312010 33400 PM 91 Nakedeye Observing Allow 510 min of dark adaptation Star charts and Voyager helpful Angles at arm s length finger width 1 fist 10 Smallangle formula yields sizes of objects at distance d good to within 5 for angles lt 45 see section 31 moon ex Size2pied angle360 yields Size dx angle573 92 Binoculars Are twin telescopes 2 telescopes 2 eyes better view Nomenclature example 7x35 means 7x magnification and front lenses 35mm in diameter Fluoride coatings minimize light loss due to reflection at airglass surfaces by softening the transition Operation 93 Telescope Properties For OSU s robotic telescope RC24 sketch Mirror diameter d 600mm normal way of describing size Focal length f 4800 mm distance from mirror to image Light collected depends on mirror s area pie dA24 partly covered lens Resolving power is limited by light s wavelike nature Smallest resolved angle for visible wavelengths is about 0116dsubmm in arcseconds compute Eye s resolution about 60 max pupil diamtere 7mm Air turbulence limit about 1 Magnification equals ratio of focal lengths ftelescope feyepiece eyepieces compute Practical minimum and maximum values are 02 dsubmm and 2 dsubmm compute 94 UV Optical and IR Instruments Cameras camera p160 JP Use a telescope s optics to focus an object s image onto a detector such as a chargecoupled device CCD A CCD is a miniature checkerboard where each square converts the light received into electrical charge that is later read by a computer Filters can be used to select the wavelengths observed Image processing is the calibration and analysis of these matrixlike image files 3 JPs Photometers Cameras optimized to measure only brightness of objects especially stars no imaging Filters can be used p68 Spectrographs Use a grating or prism to produce an object s spectrum A spectrum is a band of light that reveals how much of each color is present The spectrum is recorded by a camera CD Grating prism show spectra of flashlight and laser


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