ASTR 151 Unit 1 Study Guide
ASTR 151 Unit 1 Study Guide ASTR 151 001
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ASTR 151 001
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This 29 page Study Guide was uploaded by Wesley Fowler on Monday February 29, 2016. The Study Guide belongs to ASTR 151 001 at a university taught by Dr. Sean Lindsay in Spring 2016. Since its upload, it has received 151 views.
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Wesley Fowler ASTR 151 152 Intro to Astronomy Astro-Star Nomy-Law Oldest of the sciences Football stadium scale of the Solar System: The sun is a nickel, Earth is a grain of salt 5 1 Kilometer = 1,000m = 10 cm 11 1 astronomical unit (AU) = 1.496 x 10 m (avg distance between the earth and the sun) 1 light year (ly) = 9.46 x 10 m = 9.45 x 10 km = 63,200 AU (distance light travels in a year) 16 1 Parsec (pc) = 3.09 x 10 m = 206,000 AU = 3.26ly “One parsec corresponds to the distance at which the mean radius of the earth's orbit subtends 8n angle of one second of arc” 3.0 x 10 m/s = speed of light Giga: Billion Mega: Million Kil: Thousand Centi: .01 Micro: 10^-6 Nano: 10^-9 Earth= 12,800 km 10 Solar System= 1018m Milky Way= 10 km= 100,000 ly Virgo closest to milkyway, millions of light years? Everything is being drawn towards “The great attractor” which is made of dark matter and galaxies 100 Billion stars in milky way galaxy 100,000 light years across the galaxy 7 Seconds in a year = x 10 sec Scientific theory: Observation-theory-predictions/hypothesis-observation… Data-hypothesis-test-results Wesley Fowler ASTR 151 152 Chapter 1 Motions of the Moon Average distance between the Earth and Moon is 384,500 Km Synodic Month: Full cycle of moon phases (29.5 days) Sidereal Month: Time for moon to revolve around Earth 360 degrees (27.5 days) Synodic Period: 4 weeks The moon is always half lit, acting as a reflecting “mirror” of sunlight. Eclipses Eclipses occur when the Sun, Moon, and Earth form a straight line. When the shadows align. - Lunar Eclipse: The Earth is between the sun and the moon. Total or partial. Full Moon - Solar Eclipse: The Moon is between the sun and the earth. New Moon o Penumbra: Sun partially visible. Outer shadow o Umbra: Sun completely obscured. Inner shadow Corona: Crest of the sun. HOT Diamond Ring affect: Seeing the rim of the sun during an eclipse just before or after an eclipse. Eclipses do not occur every month because the Moon’s orbit is inclined 5.2 degrees with respect to Earth’s orbital plane. Tilted tiles. Distance Measurement What do you need? - Baseline distance - An angle () Parallax: The measurement of angular distance (apparent motion, arcsec) relative to two different background vantage points. The earth’s diameter is too short of a baseline to calculate parallax, the diameter of Earth’s solar orbit is though! Largest we can possibly have, June December. greater distance = smaller parallax angle Eratothanes’ Method: Deduced the Earth’s circumference to be 39,000km Actually 40,075km Diameter = Distance x (Angular Diameter/57.3 degrees) Wesley Fowler ASTR 151 152 Reading 1.1-1.3 Scientific Method Scientific method: The process of testing a theory via a controlled and measured experiment Theory: “The framework of ideas and assumptions used to explain some set of observations and make predictions about the real world”(8 McMiillan). Theoretical model: Result of theory, a representation. Qualifications for a theory: -Testable -Continually tested -As “simple” as possible -elegant Mapping the Universe Planet-star-system-galaxy-cluster-universe Universe: The totality of space Astronomy: The study of the universe 1 Light year= 10 trillion kilometers or 6 trillion miles -speed of light= 300,000 kilometers per sec Fixed background: The stars appear to hold relative fixed positions in the sky Constellations: Ancient observations of how stars connect into configurations. Used to pinpoint the location of stars. Smaller groupings of stars with casual names are called asterism. For example the “Big Dipper”. Celestial sphere: The simple concept that earth resides in a celestial sphere in which stars travel in a fixed relative location. Earth’s poles coincide with the universe’s poles. Divided into 88 constellations. - Right Ascension: Equates to longitude for celestial sphere, horizontal - Declination: Equates to latitude celestial sphere, vertical - The grid of locating stars and objects on the celestial sphere http://www.daviddarling.info/encyclopedia/C/celsphere.html The zodiac is comprised of the constellations that are aligned on the ecliptic. The ones that the sun passes through. Eath’s Motions Diurnal: Daily - Rise in the east, set in the west Annual: Yearly - Due to earth’s revolution, or orbital motion Sidereal: Rotation or revolution of 360 degrees. Rotation: Earth is tilted at 23.5 degrees with respect to its orbital path. In summer, the Sun rises north of east, travels through the southern sky, and sets north of west. In winter, the Sun rises South of East, travels through southern sky, and sets south of west Solar Day: Noon-to-noon (24 hours) Sidereal Day: Time for 360-degree rotation (23 hours 56 minutes) Revolution: 0.986 degrees per day If revolution increases in speed, the solar day becomes longer (catching up to noon) Seasons are determined by the Earth’s 23.5 axial tilt! The planet is closest to the sun during January, but due to the concentration of sunlight, it’s the coldest season in the north and the warmest in the south. Procession Tropical Year: Calendar year (365.2422 days) time between two Vernal Equinoxes Sidereal Year: Time needed to complete one orbit around the sun (365.256 days) Wesley Fowler ASTR Ancient Astronomy Stonehenge: An ancient astronomical observatory of sorts. Helps determine what time of year it is…useful to plan harvesting and planting crops Diurnal Motion: Sun, moon and Stars Annual Motions: The Ecliptic Prograde motion: night-to-night eastward motion -> (rights are pro) Retrogade motion: night-to-night westward motion <- (lefts are retro) Mercury and Venus are “tethered” to the sun Mars, Jupiter, and Saturn exhibit retrograde motion Inferior planets: Between earth and sun Superior planets: Outside earth from sun Opposition occurs at a planet’s closest approach to earth (Inf/superior) Conjunction occurs when a planet appears closest to the sun from the earth’s perspective (etc) Aristotle: Geocentrism. Not an experimentalist at all - The Ptolemaic Universe: Earth at center, perfect orbs and orbits. Circular orbits called epicycles. Lots of problems, planets too close to sun, etc. Copernicus: Heliocentrism (borrowed from Aristarchus) - The Copernican universe: Observed Mar’s orbital motion in comparison to Earth’s, found that Mars had a retrograde motion Retrograde motion: *Point “B” is the opposition. In line with each other 1. Earth is not at the center 2. Center of Earth is the center of the Moon’s orbit 3. All planets revolve around the sun 4. The stars are much farther away than the sun 5. The motion of the stars in the sky is due to Earth’s orbit 6. The motion of the sun in the sky is due to Earth’s orbit 7. Retrogade motion of planets is due to Earth’s motion around the sun - Still believed in perfect orbs and orbits The Team: Heliocentrism’s Establishment Tycho Brahe (1546-1601) The data collector Galileo Galilei (1564-1642) The observer Johannes Kepler (1571-1630) The analyst Galileo Used the pre-invented telescope to observe the heavens. Drew the moon. - Observed craters on the moon. Observed sun spots on the sun. Thus disproving “perfect sphere” theory - Observed phases of Venus - Observed Jupiter’s moons in orbit Tycho Brahe - Took very accurate measurements for decades (~1 arcsec) and preserved them well. - Copper nose, mysterious death. Wesley Fowler ASTR Kepler’s Laws Johannes Kepler - “Acquires” Brahe’s data and creates “Kepler’s Laws of Planetary Motion” 1. Planetary orbits are elliptical. An oval, not circular. The sun is the focus 2. Equal Areas: equal times. Fast when close to sun, slow when far away. 3. The square of the period (P, years) is proportionate to the cube of the semi-axis major (a, astronomical units) P (years) = a (AU)3 st 1 law Elliptical Orbit Perihelion: Closest to sun Aphelion: Farthest from the sun Eccentricity: How “out of circular” the ellipse is (e) Semi-major axis: Radius of major axis (a) nd 2 Law Equal areas, equal times. When plant is farthest away from the sun, it moves the slowest. When it’s closest it moves the fastest. - Fastest at perihelion and slowest at aphelion rd 32 Law 3 P (years) = a (AU) Where (P) is period and (a) is Semilunar Axis AU is defined as the Semilunar axis of Earth The Astronomical Unit Giovanni Cassini measured the earth’s semi major axis via parallax, and was pretty close! One Astronomical Unit is the distance between the Sun and Earth. *1.5 x 10 km is the AU (for this class)* - Force: (N) An influence that tends to change motion - Inertia: (kg*m ) The resistance of an object to change its speed or direction, inertia. - Mass: (kg) The amount of matter - Weight: The gravitational force exerted by an object. How mass is changed by gravity. - Speed: Distance divided by the time it takes to cover it. - Velocity: Speed and direction - Acceleration: (m/(s ))The rate of change of velocity, meters per second per second Newton’s Laws Isaac Newton: Invented Calculus, and fathered Physics. 1. Newton’s first law of motion: An object will maintain constant velocity, or its state of rest (v=0), unless acted upon by an outside force. 2. Newton’s second law of motion: An enacting force is equal to the mass times acceleration of the object it’s pushing against. F = ma - Constant Force: The greater the mass, the harder it is to accelerate the object - Constant Mass: The greater the force applied the larger the acceleration 3. Newton’s third law of motion: When one body exerts a force on the second body, the second body exerts a force equal in magnitude, but opposite in direction of the first body Gravity Th2 acceleration due to gravity’s pull towards the center of Earth: g = 9.8 m/ (s ) F = (Gm m1)/2 2 This is the “Inverse Square Law”. The farther away the object is, the weaker gravity becomes. - The gravitational force is proportional to the product on the two objects mass’s divided by the square of the distance between the two objects (Definition) Gravitational constant (G) = 6.67 x 10 N m /kg 2 2 Planets are constantly being pulled towards the sun by the sun’s gravity Orbiting masses are localized to a common focus, at the center of mass Wesley Fowler ASTR 152 Newtonian Mechanics Planetary Motion Planets don’t shoot strait ahead due to the pull of the sun’s gravity. Thus they orbit. Due to its mass, the sun is the dominant influence over planetary orbit in our solar system. - The earth orbits the sun at a speed of 30km/sec Newton’s corrections to Kepler’s first and third laws: - The earth does not orbit around the center of the sun, but rather around the center of mass between the earth and sun. The “average” position of all the matter. This is the true common focus. This point is still in the sun for the Earth, because it’s so massive. *Mass of sun: 2.0 x 30 kg - P = (a )/(M ) P-orbital period a-semimajor axis M-combined total mass of two objects in solar units Escape Velocity If an object escapes the gravitational pull of an object, then it is unbound. The orbit is no longer an ellipse! Orbital Speed: GM vorb R √ Escape Velocity: Wesley Fowler ASTR Chapter 3 Light and Radiation Thermal Radiation: Temperature and energy - Temperature is the measure of the average microscopic motion of particles, which collide, releasing energy, thus heat - Absolute zero: No motion, 0 Kelvin - Kelvin = Degrees Celsius + 273 (No degrees!) The average motion of particles Blackbody curve/spectrum: - Blackbody: An ideal object that absorbs and reradiates all forms of light perfectly (Coal is close, it absorbs 95% of light) The relationship between the intensity, or the amount of radiation (y axis), and frequency (x axis) - As temperature of blackbody increases, the peak of emission decreases to shorter wavelengths (“bluer”) Wien’s Law When things heat up to a certain temperature, they often produce a visible color. Wein’s Law: The peak of wavelength emission is inversely proportional to the temperature of the object, and is directly proportional to frequency. - /T(K) peak - “Cooler stars have longer wavelength peaks” Wavelength: Lambda () Intensity refers to “the amount of color” Equations (Don’t need to be memorized): peakm(microns)) = (2900)/T(K) peaknm(nanometers)) = (2900)/T(1000s of K)) peakmm(millimeters)) = (0.29)/T(K) The color of a star reflects its surface temperature! Hotter stars are blue, cooler ones are red. Stefan’s Law: As temperature increases, energy output increases - The total energy emission per unit of time (Flux) is proportionate to 4 temperature Flux = T 4 Flux = Power/Area = 5.67x10 W/m K (don’t need to memorize this) Power is energy per second. For Emitting objects this can be called Luminosity - For example, if you double the temperature of an area, the output of energy increases by a factor of (2)^4 = 16 **Both of these laws are used together in certain problems!** Example: If star 1 is 60K and star 2 is 600K… - Star 1: peakm(microns)) = 2900/60 = 48m - Star 2: peakm(microns)) = 2900/600 = - 4.8m 4 Star two’s flux increases by a factor of 10 Colors are both reflections of visible light, as well as emissions of light due to temperature. The Doppler Effect Relative motion influences how light and sound are perceived. Has to be towards or away from you (radial motion) - If an object is moving towards you, wavelengths seem shorter, and sound higher and appear “bluer”. - If an object is moving away from you, the wavelengths seem lower, and appear “redder” as they spread out over distance. This also applies if you are moving towards a stationary object. (Apparent wavelength/True wavelength) = (True frequency/Apparent frequency) = (Recession velocity/wave speed) - Depends on the relative motion between the source and observer, and it must have radial motion. It must move towards or away from the observer. It does not depend on distance! Wesley Fowler ASTR Chapter 3 Properties of Light Light is a form of radiation. It is the reason why we know anything about the universe. Light is also called electromagnetic radiation. Light is both a wave and a particle. Radiation is any way in which energy is transferred through space without physical connection. - Opacity: The extent as to how much radiation is blocked due to an object’s material. All light travels at the speed of light, no exceptions! (3.00x10 km/s) Wave Motion Frequency: Number of crests that pass a given point per second. Kind of like speed (hertz) - Frequency = (1/Period) Period: The time it takes for the crest of a wave to travel to another crest’s former position (s) Amplitude: The maximum departure or size of a wave from its undisturbed state Wavelength and frequency are inversely related. Big waves have small frequencies. Wavelength units: -9 Nanometer (nm) 1.0x10 m = 1nm Micrometer (m) 1.0x10 m = 1m Angstrom (Å) 10 m = 1 Å “The Single Slit Experiment” Thomas young - Proves that light can be a wave. The shadow from the experiment was fuzzy due to diffraction, it lost clarity. This shows that light can bend around corners, thus it is an electromagnetic wave. Charged Particles and Waves Electromagnetism is one of the four fundamental forces, along with gravity. Unlike gravity, electrical forces can either attract or repel objects. Light, as an electromagnetic wave, requires no medium to travel through. It is created by accelerating charged particles (protons and electrons attract, protons and protons repel) Any charged particle has an electrical field - Decreases with distance, same as gravity Any changing electrical field has a magnetic field - Moving charges create magnetic fields - Magnetic fields exert force on moving electrical charges Electrical and magnetic fields are two different aspects of Electromagnetism. They both comprise an electromagnetic wave. 5 - All electromagnetic waves travel at the speed of light (3.00x10 km/s) The Electromagnetic Spectrum: Spectrum: The division of light by specific wavelengths. In the visible spectrum, larger wavelengths are “reder”, shorter wavelengths are “bluer” - “Ultraviolet is bluer than visible light” Wavelength is typically measure in nanometers (nm) - Nano = 10 , 1 nanometer = 1x10 m (1 billion nanometers in a meter) -10 - Angstrom: (1 A = 10 m = 0.1 nm) Electromagnetic waves require no medium, unlike other types of waves. Created by accelerating charged particles. It can travel through a vacuum just fine. Atmospheric Opacity: How opaque the atmosphere is in allowing light through. 0% means unhindered passage, 100% means absolutely blocked. Wesley Fowler ASTR Chapter 4 Spectroscopy Spectroscopy is the study and analysis of how matter emits and absorbs radiation. It is the study of how light interacts with matter. - Radiation is analyzed by a spectrometer Three types of Spectra Continuous spectra: Full emission. From a blackbody source that is dense enough. Emission Spectra: Distinct lines of color in “emission” Absorption: Distinct lines of color removed by absorption - Every element has a unique set of absorption lines The radiation given off by certain gases, as observed by a spectroscope, is seen as a few narrow emission lines. These are all the colors/wavelengths not emitted. - The frequency or wavelength cannot be altered! Absorption Line: Black lines/gaps represent wavelengths that have been absorbed. Kirchhoff’s Three Laws of Spectroscopy 1. A luminous solid, liquid or gas with high-density emits a continuous spectrum of radiation (Blackbody) 2. Hot gases with low-density emit an emission spectrum with a series of bright emission lines, unique to each gas 3. Cool thin gases (along line of sight of the emitting object) emit the absorption spectrum, leaving dark absorption lines in place of certain wavelengths Atoms and Radiation Light is also a particle Quantum mechanics: The branch of physics governing the balancing of atoms and subatomic particles. Protons: Positive charge Electrons: Negative charge Neutrons: Neutral charge *The Bohr model is outdated; the electron cloud model is current. Excited state: When an electron orbiting an atom occupies a farther than normal orbital. Contains a greater amount of energy than normal. Ground State (of an atom): State of lowest energy. “Normal” When an electron achieves its maximum energy it breaks free from the nucleus’ pull, and the atom is ionized. An ion is an atom missing one or more of its electrons. When an electron drops closer to an energy level closer to the nucleus it emits energy. If it jumps away from the nucleus it absorbs energy. Atoms can only absorb or emit specific energies; each electron has an associated energy level. - The amount of energy absorbed or emitted is directly proportional to the energy difference between two electron orbitals Photons A particle of “electromagnetic energy”, the packet of energy equal to the difference between two electron orbitals. Photon energy is directly proportionate to radiation frequency, and thus inversely proportional to wavelength. Intensity is not a factor in electron energy. Shorter wavelength (blue), more energy. Longer wavelength (red) less energy E = hf = (hc)/ -34 - Planck’s constant: h= 6.63 x 10 Joule seconds (JS) - E: Photon energy (in electron volts, eV) E(eV) = 1240/((nm)) eV: The energy gained by an electron accelerated through an electric potential of one volt. - 1 eV = 1.60 x 10 -19J Wesley Fowler ASTR Chapter4 Spectral Lines and Ionization The frequencies of gases are not continuously spread out, rather they vary depending on their atomic structure. Emission lines correspond to the energy differences in an atom’s electron orbital levels. This helps us understand the composition of the universe. The energy of any state (n): E n1 3 6 .1 eV. n2 (Don’t need to memorize this) - E: Energy - eV: Electron Volt (unit) The minimum amount of energy needed to ionize hydrogen from its ground state is 13.6eV (Ionize is to free an electron from its local nucleus) The Lyman Series: Transitions starting or ending at the ground state. Ultraviolet Lines - L = 121.6nm (“Lye” on the ground) 10.2eV The Balmer Series: Transitions starting or ending at the 1 excited state. Visible Lines. - H = 656.3nm 1.9eV There are two ways that atoms/molecules can become excited - Direct excitation: Electron goes from ground state, to 1 excited state, back to ground. This releases a UV photon. nd - Cascade De-excitation: Electron goes from ground state, to 2 excited state, then either drops directly back to ground state emitting a UV photon, or it cascades down the 1 excited state to the ground state, releasing a visible and then UV photon. These lines make up the emission and absorption lines that can be seen in a spectrum! - If you view a gas cloud along sight with continuous spectrum (light bulb) we see Absorption Spectrum. - If viewed from a side angle without the continuous spectrum, we see Emission Spectrum. Hydrogen is the simplest element to teach this concept. The more electrons, neutrons, and protons in an element, the more complicated it becomes due to there being more spectral lines. Molecular Motion Electron transitions -> Visible and ultraviolet spectral lines (largest energy changes) Changes in vibration -> Infrared spectral lines Changes in rotation -> Radio and microwaves lines The strength of a spectral line (how bright or dark it is) is dependent on the amount of atoms, or concentration. It is also dependent on the temperature of the gas containing the atoms because temperature determines how atoms transition between orbitals. - At higher temperatures, more atoms are in an excited state. The radial velocity of an object can be determined by comparing the pre- determined wavelength of the element to the presently-observed color. By seeing how “reder” or “bluer” it is, astronomers can determine the radiations’ radial motion. The environment in which absorption or emission occurs causes spectral lines to broaden. Measuring the width of expansion can help determine the speed of particles. Rotation and turbulence can also be used to measure speed. Additionally, these factors also broaden spectral lines: 1) Thermal motions of particles 2) Rotation of a macroscopic object 3) Collisions between atoms 4) Magnetic Fields – Zeeman Effect Electrons and particles are moving randomly like crazy, so their observational frequency is also affected by the Doppler Effect too. The amount of collisions also alters the apparent energy, collisions dependent on the density and pressure of the gas. The more rapid a star’s motion, the broader its spectral line appears. The half rotating away is “reder”, rotation towards is “bluer”. The Zeeman Effect: The effect of splitting spectral lines into multiple components in the presence of a static magnetic field. Wesley Fowler ASTR Chapter 5 Telescopes Telescopes gather photons together for observation, and thus make faint objects brighter. - Not about magnification, but capturing light. If the size is doubled, image is 4 times brighter. Lens: A medium for light to travel through which bends light rays towards a central focus. Made out of plastic or glass. Focus: The point where all light rays converge Focal Length: The distance between the primary mirror and the focus Telescope Diameter: Edge-to-Edge length the mirror. Determines area and resolution of image Telescope Area/Collecting Area: Area of mirror, controls brightness and exposure time - Area = πr 2 Collecting area: The total area capable of gathering radiation (duh) - “The observed brightness of an astronomical object is directly proportional to the area of the telescope’s mirror and therefor to the square of the mirror diameter”. Refracting telescopes Uses the refraction of light through a lens to gather and concentrate a beam of light. Images can end up inverted. Refraction Anatomy: Prime mirror->eyepiece Problems with large scale-refractors: 1. Chromatic Aberration: “Color Error”. Each color is bent differently via refraction (hence the rainbow from a prism). This doesn’t happen with mirrors. 2. Through-put: “Light Loss”. Light is absorbed since it passes through the medium (lens). Mirrors do not absorb nearly as much light. 3. Weight deformation: Large lenses are very heavy, and can only be supported around the edges. It will stretch and deform under its own weight. Mirrors are supported at the base of the telescope; this is not a problem. 4. Polishing: A lens has two sides to be polished, while mirrors only have one Reflecting telescopes Uses a series of mirrors to reflect and focus incoming light. Light travels to primary mirror, reflects off its curved surface to secondary mirror, which then reflects to eyepiece. Reflecting Anatomy: Prime mirror->Secondary mirror- >eyepiece Types of reflecting telescopes: - Prime focus: Observe via the prim focus at the top. You stand in the path of the incoming light. Radio telescopes. - Newtonian telescope: Small mirror directs light out to the side in a small hole 90 degrees out. Invented by Newton. - Cassegrain telescope: Small mirror directs light towards the base of the telescope, in-between the primary mirror. - Nasmyth focus/coude room: Three mirrors allow for flexibility. - Gregorian: Two primary mirrors allow gap at base for observation from secondary mirror. Photometry: Angular resolution: The ability of an object to distinguish or separate objects close together in one field of view. Larger telescopes have better angular resolution. (Arcseconds, ArcMinutes, Degrees…) - Smaller number for resolution means more fine detail. Photometer: A device that measures the total amount of light received in all of or the specified area in the field of view. - To determine a star’s photometry, astronomers add up the values of all the CCD pixels focused on that star. Sounds simple, but images often overlap with each other. To counteract this, filters are used to distinguish particular wavelengths. Charge-coupled devices (CCD): Hundreds of millions of pixels (made of silicon) are electrically charged whenever light hits. The amount of charge is directly proportional to the amount of photons striking each pixel. - They record 90 percent of photons striking the area - What’s in our phone cameras - Large dynamic range, see faint and bright objects - Gives actual data to work with Observation “Seeing” refers to the angular resolution of a telescope, which is usually 1 arc second. Seeing disc: The circle over which a star’s light is spread for observation. Altered by limiting factors. Limiting Factors: *Turbulence interferes with telescopes and early image processors (pre- 1990) because the wind blurs the images of stars! For high resolution images, must be precise. *Light pollution, upward directed light from streets scatters from air dust to telescopes obscures seeing discs. Why astronomers go to remote areas. Solutions: - Space telescopes/high elevations - Avoid light pollution - Active Optics: Controlling the environment in which telescopes operate (ie temperature) - Adaptive Optics: A computer intentionally deforms the mirror’s shape to to compensate for the atmospheric turbulence. Angular resolution as low as 0.06” Wesley Fowler ASTR Chapter 5 Radio Astronomy The atmosphere is no hindrance to long-wave radiation, they’re safe for us and are easy to observe from earth. - Karl Jansky is the man, started radio astronomy in 1931: Observed “hisses” in radio interference every sidereal day. Those turned out to come from the center of the galaxy Incoming radiation bounces off of collecting area/dish, to focus, down to detector, which goes to a computer - Have to be large to get a sufficient amount of data *Works 24 hours a day, even when it’s cloudy, or when it’s storming. *Radio waves are generally unaffected by intervening matter *Poor resolution though Radio waves can travel through interstellar dust, revealing images behind the cloud. Greenbank Radio Telescope: Largest steerable single dish, best for 1cm radiation - Arecibo Telescope: Largest single dish telescope in the world -> - The Haystack Observatory: 37m radio telescope *Longer wavelength telescopes do not require as smooth surfaces Interferometry: Using two or more radio telescopes to observe one object at the same wavelength, then sending the combined data to one central computer. Can span huge distances - Resolution is equal to a single telescope with a diameter of the largest distance between two of the telescopes. This applies to more than radio astronomy! Interferometry has application to other/higher wavelengths, since technology has been improving over the years. Low Frequency Astronomy Infrared Astronomy: Observes wavelengths that are in-between visual and radio frequencies. Often use balloons, airplanes, rockets to observe above the atmosphere. Orbit in space too! - Allows observations of dust structure, instead of just a blur +Spitzer Space Telescope: Wavelengths of 3.6-160 (um) cooled to 4 kelvin with liquid Helium +Herschel Space Observatory: 50-700 um Can penetrate interstellar dust! Outlines dust. Microwave Astronomy: Good for viewing cold interstellar dust High Frequency Astronomy Ultra-Violet Astronomy - Primarily used to observe gases between stars - Good for young, very hot stars as well as star formation regions X-Rays and Gamma Ray Astronomy: These wavelengths do not reflect off any surfaces easily. They tend to pass straight through, or be absorbed. Useful for studying extremely hot gases. - CCD’s do not work well for these at all X-Ray telescopes use grazing incidence by using cylindrical mirrors to focus light. Individual photons must be counted by orbiting devices, and then transmitted down to a computer. - The number of photons in the universe appear to be inversely related to their frequency
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