Unformatted text preview:

Test #1, Tuesday, Feb 9Clicker Question:Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13HI absorption in 1946+708 Peck & Taylor (2001) “Global” VLBI observations core: FWHM = 350 km/s M ~ 108 MsunSlide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Test #1, Tuesday, Feb 9I will post a review for Test 1 in the A101 homepage under the link to “Lectures” this week. I will tell you the topics to review and how to go about doing that. I will also tell you what to bring for the test.Clicker Question:Compared to visible light, X-rays travel:A: fasterB: slowerC: at the same speedClicker Question:Compared to sound waves, radio waves travel:A: fasterB: slowerC: at the same speedClicker Question:Electromagnetic radiation penetrates the Earth’s atmosphere at what wavelengths?:A: at visible, ultraviolet, and gamma-ray wavelengthsB: at all wavelengthsC: only at infrared wavelengthsD: only at optical wavelengthsE: at radio, visible, and part of the infrared wavelengthsRadiation travels as waves.Waves carry information and energy.Review: Properties of a wavewavelength ()crestamplitude (A)velocity (v)trough is a distance, so its units are m, cm, or mm, etc.Period (T): time between crest (or trough) passagesFrequency (): rate of passage of crests (or troughs),  Also, v = 1T(units: Hertz or cycles/sec)Example: Blackbody - the microwavebackgroundSpectroscopy and AtomsHow do you make a spectrum?For light, separate white light into its colors using a glass prism or "diffraction grating". For radiation in general, spread out the radiation by wavelength (e.g car radio, satellite TV receiver).We can use these things to determine:- Physical states of stars, gas clouds, e.g. temperature, density, pressure.- Chemical make-up of stars, galaxies, gas clouds- Ages of stars and galaxies- Masses of stars, clouds, galaxies, extrasolar planets, rotation of galaxies,expansion of universe, acceleration of universe.All rely on taking and understanding spectraTypes of Spectra1. "Continuous" spectrum - radiation over a broad range of wavelengths(light: bright at every color).3. Continuous spectrum with "absorption lines": bright over a broad range of wavelengths with a few dark lines.2. "Emission line" spectrum - bright at specific wavelengths only.Kirchhoff's Laws1. A hot, opaque solid, liquid or dense gas produces a continuous spectrum.2. A transparent hot gas produces an emission line spectrum.3. A transparent, cool gas absorbs wavelengths from a continuous spectrum, producing an absorption line spectrum.The pattern of emission (or absorption) lines is a fingerprint of the element in the gas (such as hydrogen, neon, etc.)For a given element, emission and absorption lines occur at the same wavlengths.Sodium emission and absorption spectraDemo - SpectraSpectrum of Helium (He) GasDiscovered in 1868 by Pierre Jannsen during a solar eclipseSubsequently seen and named by Norman LockyerExample: spectra - comet HyakutakeHI absorption in 1946+708Peck & Taylor (2001)“Global” VLBIobservationscore:FWHM = 350 km/sM ~ 108 MsunThe Particle Nature of LightOn microscopic scales (scale of atoms), light travels as individual packets of energy, called photons.cphoton energy is proportional toradiation frequency:E  (or E 1example: ultraviolet photons are more harmful than visible photons.The Nature of AtomsThe Bohr model of the Hydrogen atom:_+protonelectron"ground state"_+an "excited state"Ground state is the lowest energy state. Atom must gain energy to move to an excited state. It must absorb a photon or collide with another atom.But, only certain energies (or orbits) are allowed:___+The atom can only absorb photons with exactly the right energy to boost the electron to one of its higher levels.(photon energy αfrequency)a few energy levels of H atomWhen an atom absorbs a photon, it moves to a higher energy state brieflyWhen it jumps back to lower energy state, it emits a photon - in a random directionOther elements Helium Carbonneutron protonAtoms have equal positive and negative charge. Each element has its own allowed energy levels and thus its own spectrum.So why absorption lines?...........cloud of gasThe green photons (say) get absorbed by the atoms. They are emitted again in random directions. Photons of other wavelengths go through. Get dark absorption line at green part of spectrum.Why emission lines?......hot cloud of gas- Collisions excite atoms: an electron moves into a higher energy level- Then electron drops back to lower level- Photons at specific frequencies emitted.Ionization+Hydrogen_++Helium"Ion"Two atoms colliding can also lead to ionization.__Energetic UV PhotonAtomEnergetic UV PhotonClicker Question:Astronomers analyze spectra from astrophysical objects to learn about:A: Composition (what they are made of)B: Temperature C: line-of-sight velocityD: Gas pressuresE: All of the aboveClicker Question:Ionized Helium consists of two neutrons and:A: two protons in the nucleus and 1 orbiting electronB: two protons in the nucleus and 2 orbiting electronsC: one proton in the nucleus and 1 orbiting electronD: one proton in the nucleus and 2 orbiting electronsE: two protons in the nucleus and 3 orbiting electronsClicker Question:Why is the sky blue?A: Molecules in the atmosphere scatter red light more than blue light.B: Molecules in the atmosphere scatter blue light more than red light.C: Molecules in the atmosphere absorb the red light D: The sky reflects the color of the oceans.Stellar SpectraSpectra of stars are different mainly due to temperature and composition differences.Star'Atmosphere', atoms and ions absorb specific wavelengths of the black-body spectrum Interior, hot and dense, fusion generates radiation with black-body spectrumWe've used spectra to find planets around other stars.Star wobbling due to gravity of planet causes small Doppler shift of its absorption lines.Amount of shift depends on velocity of wobble. Also know period of wobble. This is enough to constrain the mass and orbit of the planet.As of today 270 extrasolar planets known. Here are the first few discovered.MoleculesTwo or more atoms joined together.They occur in atmospheres of cooler stars, cold clouds of gas, planets.ExamplesH2 = H + HCO = C


View Full Document

UNM ASTR 101 - Study Guide

Download Study Guide
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Study Guide and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Study Guide 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?