Discover the Universe Week 3
Discover the Universe Week 3 AST 1002
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This 10 page Class Notes was uploaded by Jocelyn on Friday September 11, 2015. The Class Notes belongs to AST 1002 at University of Florida taught by Reyes, Francisco J in Summer 2015. Since its upload, it has received 173 views. For similar materials see Discover the Universe in Science at University of Florida.
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Date Created: 09/11/15
Tuesday September 8 2015 Discover the Universe Week 3 Ch1 Continued The mutual gravitational attraction between the Sun and the planets is responsible for their motion Kepler s Third Law Revisited The Sun and the Earth both orbit their mutual center of mass which is inside the Sun The Sun moves very little bigger mass while Earth moves a lot smaller mass The Center of Mass the average position of the matter comprising the two bodies m1d1 m2d2 Kepler s First Law Revised The orbit of a planet around the Sun is an ellipse having the center of mass of the planetSun system at one focus ASSUME that when asked about Kepler s first law that it is about the original version unless specified for this modified version Kepler s Third Law Revisited Includes both the mass of the central body and the mass of the orbiting body PA2 aA3 M total M Sun M total M Sun M planet is about M Sun An application with Jupiter a mean distance P orbital period M total M Jupiter M lo gt since the mass of lo can be neglected substitute the proportional sign for an equal sign M Jupiter aA3 PA2 The mass of Jupiter will be given in solar mass Tuesday September 8 2015 This equation allows to compute the mass of the black body located at the center of the milky way using the mean distance and the orbital period of a star orbiting the black hole Chapter 2 Light and Matter All we can receive from stars and galaxies is light since they are too far away From light we can learn composition temperature speed etc Active Galaxy NGC New General Catalogue 5128 radio source Centauras A If you use visible light you cannot see the inside of the galaxy as opposed to when using infrared light Q ampA 1 How do astronomers learn about the chemical elements that make up stars and galaxies 2 How do they know about the temperature of planets stars and galaxies 3 How do they know about the speed at which they are moving 9K Through the interpretation of light or the electromagnetic radiation received from these objects 9K Electromagnetic radiation refers to waves in which the energy is carried in the form of oscillating electric and magnetic field 9K Visible light is a particular type of electromagnetic radiation visible to the human eye Tuesday September 8 2015 Light behaves like a wave or a particle For example a wave is a way i which energy is transferred from place to place without physical movement of material from one location to another such as the ripples on the surface of a pond when a pebble is dropped Wave Characteristics 1 Wavelength 2 Amplitude 3 Frequency 4 Wave Speed Amplitude r 1 A A j d v V a l J Trough Wavelength r a 1 For light c wavelength x frequency c lambda x f lambda wavelength f frequency Wavelength lambda measured in length m cm nm etc Distance between successive wave peaks Period units of time seconds The time between passing wave crest Frequency f units hertz Hz 1 s multiples kHz MHz Number of vibrations per unit time Thursday September 10 2015 Frequency 1 Period Important Light all wavelengths travels in vacuum at the same speed C 300 000 kms Electrically charged particles and electromagnetic waves Electrons have a negative charge Protons have a positive charge Electromagnetic waves the changing position of a charged particle creates these types of waves Travel through empty space leading them to eventually interact with a distantly charged particle Visible light is an example of an electromagnetic wave Magnetism Magnetic field produced from moving electric charges Examples Electric current passing through a coil electric motors Earth s magnetic field is produced by the spinning of charges in the liquid metal core of the Earth Magnetic fields force charged particles to move locations Accelerated charges electrons protons produce Ripples in the ElectroMagnetic E ampM field 39 E ampM Waves LIGHT An electromagnetic wave is composed of two oscillating fields 1 an electric field and a 2 magnetic field that are perpendicular to each other Wavelength means COLOR Visible light ranges in wavelength from 400 to 700 nanometers Visible light is a SMALL part of the electromagnetic spectrum The shorter the wavelength the higher the frequency vice versa Thursday September 10 2015 ELECTROMAGNETIC SPECTRUM Visible Light 700nm 600nm 500nm 400nm v Radio waves Microwaves Infrared Ultraviolet Xrays Gamma LONGER WAVELENGTH meters SHORTER gt I l l I l I l l I l I l l I l I l 102 11 1 101 1o 2 103 104 105 106 1o 7 108 109 1010 1011 1012 1013 The Temperature Scale Comparison of Kelvin Celsius and Fahrenheit scales The scales predominantly used in physics and astronomy is Kelvin K Temperature Scales Fahrenheit Celsius Kelvin Boiling Point of 212 F 100 C 37315 K Water Highest Temp A 134 F 561 C 330 K ever recorded in US Freezin Point 0 32 F 0 C 27315 K 393 we 0 F 18 C 255 K Moon at o o quots coldest 280 F 173 C 100 K Absolute a Zero y 460 F 273 C 0 K Thursday September 10 2015 Blackbody Radiation Atoms and molecules that make up matter are in constant motion Atoms and molecules are normally neutral The temperature of an object measures the amount of microscopic motion of its particles Kinetic Energy E 12 m vA2 m mass of the body v velocity don t forget to square When the charged particles change their state of motion through a change in direction acceleration or speed electromagnetic radiation is emitted Thermal Radiation A body at a temperature higher than 0 K will emit a blackbody Hotter blackbodies are brighter and bluer nm nanometer 1 nm 10quot 9 m 15000 K star IF C Sun 5800 K 1039 i 8 gt 10 b 15 30C0 K star 3 l1 Ii 0 i C o 3 E 10 h 310Khuman 10quot 103quot 105 10 10 wavelength rm Thursday September 10 2015 Wien s Law Hotter bodies radiate more strongly at sorter wavelengths they re bluer Cooler bodies radiate more at longer wavelengths they re more red There is a wavelength at which the intensity of the radiation reaches a maximum lambda max Lambda Max 29 cm Temperature K Stefan s Law Hotter blackbodies are brighter overall at every wavelength 13 G I where O sigma 567 x 10398 Wm39Z K394 and T is the temperature in Kelvin Rather than E we use F where F total radiative flu total energy radiated per second Total radiated flux or total energy radiated per second is proportional to the area under the black body curve Application of Stefan s and Wien s Laws Stefan s Law Increasing the temperature from 6000 K to 12000 K of a black body will increase the total radiated flux total energy radiated per second by a factor of 16 The total radiated flux is proportional to the area under the curve In this case the area under the 12000 K curve is 16 times larger than the area under the 6000 K curve Wien s Law lambda max 2900000 nm TK The lambda max shift from the visual around 483 nm greenyellow for a 6000 K to around 242 nm ultraviolet for a 12000 K Thursday September 10 2015 Stellar Colors Reddish coolest stars 3000 K Orangeish Sun 6000 K Yellowish Sun 6000 K Bluish hottest stars 50000 K Flux 400 mu wavelength mm Stars light bulbs irons etc are all blackbodies with different colors depending not heir temperature A blackbody is perfect emitter and absorber Comparison of blackbody curves from four astronomical objects Binary star Albireo Beta Cygni aka the Gator Star Temperature of the orange star 4080 K Temperature of the blue star 13200 K Thursday September 10 2015 Spectroscopy Analysis of Spectra Light can be separated into different wavelengths corresponding to colors that produce a spectrum The instrument used to produce and analyze a spectrum is known as a spectroscope A spectroscope consists of an opaque barrier with a lit to produce a narrow beam of light a prism or a diffraction grating and a detector such as the eye or a screen to project it Each element produces its own unite pattern of lines 3 types Continous Absorption Emission Absorption Line Spectra The H Hydrogen letter followed by a Greek letter is used for the Balmer series Visible H Lines aka Spectrum of the Sun Hydrogen Absorption Spectrum Hydrogen Emission Spectrum 700nm 400nm H Alpha Line 656nm Transition N3 to N2 Kirchhoff s Laws of Radiation 1859 Kirchhoff s First Law Hot dense gases or solids produce a continuous spectrum and emit light at all wavelengths Example Light bulb filament Thursday September 10 2015 Kirchhoff s Second Law A hot lowdensity gas when excited by an electric current or UV emission produces an emission line spectrum These lines are characteristic of the chemical composition a gas Kirchhoff s Third Law A lowdensity cool gas in front of a hot continuous source produces an absorption line spectrum These lines are characteristic of the chemical composition of the gas Nature of Atoms 3 subatomic particles 1 2 3 proton positive charge neuton proton electron no charge electron negative charge The nucleus is composed of protons and neutrons If an atom loses or gains an electron it acquires an electric charge It is said to be ionized and it is therefore an ion Atoms can bond with other atoms of the same kind or different kind to form molecules Example Oxygen 02 or Water H20 Each atom of a given element contains a specific number of protons and electrons this making that element unique Bchr s Hydrogen Model 1913First explanation of Hydrogen s spectral lines Electron orbits the proton nucleus kept in place by the Coulomb Force Fc Ground State 2 innermost ring lowest energy Excited State 2 higher energy Electrons can only be in particular orbits energy states Energy is quantized Excitation requires energy to be added to Nucleus 18 Energy Mel r wotx 2 electrons ma V 2nd Energy Level 8 electrons max the atom Deexcitation requires energy to be released from the Menergmg V 18 electrons max atom 10 Electron Energy Levels
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