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AS101week 7 - week 11.docx

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Department
Astronomy
Course
AS101
Professor
Victor Aurora
Semester
Fall

Description
AS101 Electromagnetic Spectrum, Doppler Effect 4.1  Modern astronomers analyze light to investigator the compositions motions internal processes and evolution of celestial objects Light as a wave and particle  Light is composed of a combination of electric and magnetic waves that travel through empty space o Do not require a medium and this can travel through a vacuum  Electromagnetic radiation: changing electric and magnetic felids that travel through space and transfer energy fro one place to another o Visible light o Associative with periodically repeating disturbance (wave) that carries energy * Analogy: waves in water: disturb water; waves spread across surface, measuring the distance between peaks is the wavelength*  Wave length: the distance between successive peaks or troughs of a wave represented by a lowercase Greek lambda  Speed of light: 300 000 km/s – the changing electric and magnetic fields of electromagnetic waves o Radiation: refers to anything that spreads outward from a source Electromagnetic Spectrum  Type of electromagnetic radiation arranged in order of increasing wave length  Rainbow is a spectra of visible light  Visible light have different wave lengths ranging from 400 nm – 700 nm OR 4000A- 7000A o Red longest violet shortest o Average wave length 0.0005 mm  Describe wave length in nanometer (nm) a unit of distance equaling one billionth of a meter (10^-9) or angstrom (a) a unit of distance commonly used to measure the wavelength of light (10^-10m)  Beyond red lies infrared radiation (ir): the proportion o the electromagnetic spectrum with wavelengths longer then red light ranging form 700 nm to 1mm between visible light and radio waves o Not sensitive to eyes but skin o Discovered y William Herschel  Radio waves have longer wave lengths: o AM wavelengths of a few hundred meters o FM and military few tens of cm to a few tens of m  Ultraviolet (UV): the portion of the electromagnetic spectrum with wavelengths shorts than violet light between visible light and x-rays  X-rays: electromagnetic waves with wavelengths shorts then UV light  Gamma rays: the shortest wavelength electromagnetic waves  Photon: a quantum of electromagnetic energy that carries an amount of energy that increase proportionally with its frequency but decreases proportionally with its wavelength o Amount go energy depends on the wavelength o Shorter wavelength; carry more energy; longer: less energy o Photon go visible light caries small amount of energy; x-ray carries a lot of energy  Electromagnetic radiation carries all the available clues to the nature of planets starts and celestial objects  Gamma and x rays are absorbed in earths atmospheres and in ozone (O3) altitude of 30 km absorbs UV, water vapor absorbs long wavelength IR radiation  Only visible light and some radio waves read earths surface through atmospheric windows: wavelength regions in which our atmosphere is transparent at visual radio and some infrared wavelengths 4.4 Imaging systems and photometers  Photographic plate: first image recording device used with telescopes o Brightness of objects imaged on a photographic plate can me measured with hard work; only a moderate precision  Photometers: sensitive light meters or measure the brightness f individual objects  Charge-coupled devices (CCDS) as image recording devices and photo meters o Specialized computer containing a million microscopic light detectors arranged in an array o Array detectors: can be used like a small photographic plate o Detect both bright and faint objects in a single exposure o Digitalized or converted to numerical data and can be read by computers  Manipulate images to produce false color images: in which the colors represent different levels of intensity and are not related to the true color of the object o Negatives all the faint parts of the image easier to see Spectrographs  Analyze detail in detail by spreading the light out according to wavelength into a spectrum  Newton: admitted a thin beam of light into darkened room, hit the prism; white light turned into a spectrum therefore, white light is composed f a mixture of all the colors  Since violet is the shortest, it bends most, red bends lest therefore creating a spectrum when the wavelengths passing through the prism are bent  Grating: piece of glass with thousands of microscopic parallel lines scribed onto its surface o Used in place of a prism  Different wavelengths of light reflect from the grating at different angles spread light out into spectrum then recorded  Recording spectrum of far away star of galaxy requires long time exposure resulting in the development of multi object spectrographs record spectra of as many as 100 objects The Doppler Effect  The observed change in the wavelength of radiation de to a source moving towards of away from the observer  Used to measure the speed of blobs of gas in the suns atmospheres and the speed of stars and galaxies  Small shifts in the wavelength of electromagnetic radiation o Sound waves: the pitch of a sound is determined by its wavelength  Long wavelength: low pitches, short wavelength: high pitches Light source emitting waves continuously  As it approaches you, light appear to have a shorter wavelength making it slightly bluer o Blue shift: Doppler shift towards shorter wavelengths caused by a source approaching the observer the faster the source approaches the larger the blue shift  As it moves away has a longer wavelength and appears redder o Redshift: Doppler shift towards longer wavelength caused by a source receding form the observer faster the source moves away the larger the redshift - Refer to any range of wavelengths  X-rays, gamma, red or blue refers to the direction of the shift no actual color  Shift from blue and red reveals the relative motion of wave source and observer  Amount of change in wavelength depends on the speed of source o Measure a speed of star by measuring size of the Doppler shift of its spectral lines  Radial velocity: that component of an objects velocity directed directly away from or towards Earth o Star moving perpendicular to line of sight ex. Directly to the left who have no red or blue shift as its distance from earth is not increasing or decreasing Week 8:Light and Matter, Telescopes 11/12/2013 5:08:00 PM 5.2 Properties of Blackbody Radiation Basic Terms: Atom: smallest unit of a chemical elements consisting of a nucleus containing protons and neutrons surrounded by a cloud of electrons Nucleus: the central core of an atom contains protons and neutrons that carry a net positive charge Proton: positively charged atomic particle contained in the nucleus of an atom Neutron: an atomic particle contained in the nucleus with no charge and Sam mass as a proton Electron: low mass atomic particle carrying negative charge Molecule: tow or more atoms bound together Heat: energy stored in a material as agitation among its particles Temperature: a measure of the agitation among the atoms and molecules of a material Kelvin temperature scale: temperature scale starting at absolute zero (- 273 degrees Celsius) Absolute zero: the theoretical lowest possible temperature at which a material contains no extractable heat energy Blackbody radiation: tradition emitted by a hypothetical prefect radiator. The spectra is continuous and the wavelength of maximum emission depends on the blackbody’s temperature Wavelength of maximum intensity: the wavelength at which a perfect radiator emits the maximum amount of energy. Depending only on objects temperate Atoms and Subatomic Particles  Atoms have a massive compact nucleus containing positively charged protons, paired with neutral charged neutrons and embedded within a large cloud of low mass negatively charged electrons  When the change in motion of a charged particle, the change in its electric felid spreads outward at the speed of light as electromagnetic radiation Temperature, heat and Blackbody Radiation  Particles inside any object are in constant motion o More agitated in hot objects than cold o Thermal energy  Feel heat when thermal energy is passed through your fingers  Temperature is the number of related to the average speed of particles and intensity of its motion  Temperature of the sun and other objects expressed in K o Water freezes at 273 K and boils at 373 K  Kelvin scale useful as it is based on absolute zero and is related directly to the motion of particles in an object  Hot objects glow as there is more motion among particles; collide with each other and when electrons are accelerate part of the energy is carried away as electromagnetic radiation  Radiation emitted b an opaque object is blackbody radiation  At room temp; absorber would be black high temps visibly glow o In astronomy; refers to the glowing of objects  Light energy emitted by incandescent light bulb: o Electricity passed through filament of bulb heats to a high temp = glows  Two laws that describe how blackbody radiation works: o Weins Law: the hotter a glowing object is the shorter will be its wavelength of maximum intensity inversely proportional to its temperature  The hotter an object; the faster the particles travel, collide violently, emit more energetic photons  Hot object emit radiation at shorter wavelengths; look blue o Stefan Boltzmann law: hotter object emit more energy than cooler ones of the same size, in proportion to the fourth power of temperature  The more rapidly its particles move the more frequent and violent collisions occur; producing photons  Temp determines the colour of a glowing black body  Rigel is hotter appears blue (wiens law) o Produces more energy from each square meter of its photosphere; produces more energy (Boltzmann’s law) - Human body emits infrared radiation at 310 K o Wavelength maximum intensity in the infrared part of the spectrum 5.4 Light Matter and Motion If light did not interact with matter nothing would exist Key Terms: Coulomb force: the electrostatic force of repulsion between like charges or attraction between opposite charges Ion: An atom that has lost or gained one or more electrons Ionization: the process in which atoms lose or gain electrons Binding energy: the energy needed to pull an electron away from its atom Quantum mechanics: the study of behavior of atoms and atomic particles Permitted orbit: one of the unique orbits that an electron may occupy in an atom Isotopes: atoms that have the same number of protons but a different number of neutrons Energy level: one of the rungs of the ladder of allowed energies an electron may occupy in an atom Excited atom: an atom in which an electron has moved from a lower to a higher energy level Ground state: the lowest permitted electron energy level in an atom Quantum leap: jumps of electrons from one orbit or energy state to another Electron Shells  Electrons are bound to the atom but the attraction between their negative charge and positively coulomb force  For an atom to go through ionizations needs to be an amount of energy to pull an electron away form nucleus – electrons binding energy  Size of electrons orbit related to the energy that binds it to the atom o Orbits close-tightly bound; large amount of energy needed to pull it away- binding energy large o Orbits farther- loosely bound; small amount of energy needed to pull it away – binding energy low  Nature permits atoms a certain quanta of biding energy; quantum mechanics  Because atoms have certain amount of binding energy; permitted orbits o Steps in a staircase; electron can occupy any permitted orbit but not orbits in between  Arrangement of permitted orbits is dependent on the charge of the nucleus; depends on the protons  Ionized elements have different orbital pattern than un-ionized form  Isotopes have almost same because same number of electrons different amount of protons Excitation of Atoms  Each orbit in atom represent specific binding energy; energy level o Electron in its smallest and most tightly bounds orbit is in its lowest permitted energy level o Move the electron by supplying enough energy to make the difference between the two levels  Moving an electron from low level to high level; excite the atom o If electron is moved and then falls back to lower energy level; energy is released  Can become excited by collision; one atom or both may have electrons knocked into higher energy levels  Absorb photon (packet) or electromagnetic radiation. Must have exactly the right amount of energy corresponding to the difference between levels can move electron. Has too much or too little energy atom cannot absorb it  Energy of photon depends on its wavelength only photons of certain wavelength (colour) can be absorbed by a given atom o Excited atom is unstable and eventually give up energy it has absorbed and return its electron to a lower energy level called ground state o When the electron drops it moves from a loosely bound level to more tightly bound o Atom then emits a photon as it has a surplus of energy  These jumps are known as quantum leaps o Represents a change in motion which electromagnetic energy is either absorbed or released  The colour emitted (wavelengths) emitted and absorbed by electrons is the difference between the levels not its start or finish point Common in neon signs: Atoms of neon gas in the glass tube are excited by electricity flowing though the tube -Electricity excites the neon atoms by collision; the neo atoms drop to a lower energy level almost instantly therefor-releasing photon of light 5.5 Suns Atmosphere Formation of Spectra Spectra of light from the sun and other stars are formed as light passes from their photospheres outward through their atmosphere. Properties of spectra: 1. Three types of spectra, described by three rules (Kirchhoff’s Law) a. See a spectra you can recognize the arrangement of matter that emitted the light b. Dark (absorption) lines in the sun’s spectrum are caused by atoms in either the sun or earth’s atmospheres c. The photosphere itself produces a blackbody (continuous) spectrum 2. Each atom has a unique absorption and emission spectrum  The wavelengths of photons that are absorbed by a given type of atom are the same as the wavelengths of the photons emitted by that types of atoms; both are determined by electron levels o Atom may produce multiple lines of infrared or ultraviolet, human eye can only see 3 3. Spectra is displayed as graphs of intensity versus wavelength Atomic Spectra 1. Light bulb: filament emits a continuous spectrum, blackbody radiation  An absorption spectrum results when radiation passes through a cool gas  Atoms in the gas absorb photons of certain wavelengths, missing from the spectrum o See their positions as dark absorption lines called dark-line spectra  An emission spectrum is produced by photons emitted by an excited gas o See emission lines by observing the photons of the excited atoms near the bulb; bright line spectra a. Spectrum of star is an absorption spectrum, denser layers of the photosphere emit black body radiation, gases in atmosphere absorb wavelengths and form dark line spectra b. Kirchhoff’s laws are as follows: Law I: the continuous spectrums o Solid. Liquid or dense gas excited to emit light will radiate at all wavelengths and produce a continuous spectrum Law II: The emission spectrum o A low-density gas excited to emit light will do so at specific wavelengths and thus produce and emission spectrum Law III: Absorption Spectrum o Light comprising a continuous spectrum passes through a coil low-density gas the result will be an absorption spectrum 2. When an electron makes a transition from one orbit to another, it changes the energy stored in the atoms. a. Transitions in hydrogen atom grouped into 3 series; Lyman series. Balmer series, Paschen series 3. Spectra are converted into graphs of intensity versus wavelengths Week 9: Telescopes II – Modern Observatories, Solar System Forensics 4.3 observations on Earth- Optical and Radio  Optical observers avoid cities due to light pollution  Weak radio signals from the cosmos are easily drowned out by human radio interference – automobiles  Telescopes are place on the top of high mountains fare from civilization because the dark sky and god seeing make it with the difficulty o 1. Research telescopes must focus their light to positions at which cameras and other instruments can be placed o 2. Small telescopes can use other coal arrangement that would be inconvenient in larger telescopes  Telescopes located on the surface of the earth, (optical or radio) move continuously to stay pointed at a celestial object as earth turns on its axis o Sidereal tracking: the continuous movement of a telescopes to keep it pointed at a star a Earth rotates  VLT (very large telescope) high in the remote Andes Mountains of northern Chile o Consist of 4 telescopes each computer controlled o Largest steerable radio telescope in the world is the National Radio Astronomy Observatory in West Virginian- reflecting surface of 100m in diameter o Largest radio dish is 300 m wide, built into mountain valley in Arecibo Puerto Rico 4.5 Airborne and Space Observations The Ends of the Visual Spectrum  Near infrared just beyond the red end of the visible spectrum because some of this radiation leaks through the atmosphere in narrow, atmospheric windows tanging in wavelengths form 1200 nm to 30 000nm o Usually describe wavelengths in micrometers or microns (10^-6), wavelengths range from 1.2- 30 microns o Most of radiation absorbs by water vapor and carbon dioxide molecules in earth’s atmosphere  The far-infrared range which includes wavelengths longer than 30 microns tell us about planets comets forming stars and cool objects,
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