Discover the Universe Week 5
Discover the Universe Week 5 AST 1002
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This 9 page Class Notes was uploaded by Jocelyn on Sunday September 27, 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 20 views. For similar materials see Discover the Universe in Science at University of Florida.
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Date Created: 09/27/15
Tuesday September 22 2015 Discover the Universe Week 5 Chapter 3 Cont d Photometry and Timing A light curve represents a series of brightness measurements made over a period of time The technique uses a reference star that shows no change in brightness The brightness of the variable star is calibrated against the reference star Application measuring the variation of brightness from a star allows us to detect the transit of an exoplanet in front of a star Exoplanet planet in orbit around other stars To Summarize The two most important properties of a telescope are The collecting area determines how much light a telescope can gather The angular resolution is the minimum angular separation a telescope can distinguish Both of these properties improve when the diameter of the lens or primary mirror increases The two basic design of telescopes are Refracting telescopes focus light with lenses Reflecting telescopes focus light with mirrors The majority of professional telescopes are reflectors What can astronomers do with telescopes Imaging Spectroscopy Photometry Astronomy Timing Tuesday September 22 2015 Atmospheric Blurring How does Earth s atmosphere affect groinbased observations The best groundbased sites for astronomical observations are Calm atmosphere not too windy atmosphere less turbulent High altitude less atmosphere to see through less absorption Dark Sky far from city light low light pollution Dry Few cloudy night Light Pollution Scattering of humanmade light in the atmosphere is a growing problem for astronomy Effect of Atmospheric blurring in the formation of an image The light coming from a star comes from a point source the ray will add or subtract causing the image to twinkle The light coming from a planet comes from many points in the disk Planets normally do not twinkle If the atmosphere is turbulent the diameter of the disk is large A condition called bad seeing Adaptive Optics A technique to reduce the effect of the atmosphere Rapidly changing the shape of a telescope s mirror it can compensate for some of the effects of turbulence Without Adaptive Optics With Adaptive Optics Tuesday September 22 2015 Locations of Observatories in a calm high dark and dry place The best observing sites are stop remote mountains Some of the best places are Hawaii and Chile The Hubble Space Telescope In orbit since 1990 24m diameter mirror solid It can observe in near UV visual and IR 25 billion James Webb Telescope 65m in diameter 1 hexagonal mirrors Projected launch date 2018 Mainly instruments for the IR 8 billion TMT Thirty Meter Telescope A comparison of the rise of the mirrors in the 30 m TMT with the 10 m Keck and the 5 m 200 inch hale mount Palomar telescopes The primary mirror is composed of 492 segments It will be located at the Mauna Kea observatory Hawaii Projected date for beginning of operations is 2022 12 billion Transmission in Atmosphere Only the longer wavelengths of radio and the visible light pass easily through Earth s atmosphere We need telescopes high in the atmosphere to observe in the IR part of the spectrum Tuesday September 22 2015 How does Earth s atmosphere affect ground based observations Telescope sites are chosen to minimize the problems of light pollution atmospheric turbulence and bad weather 64 telescopes and technology How can we observe invisible light A standard satellite dish is essentially a telescope for observing radio waves it is called a radio telescope Radio Telescopes A radio telescope is like a giant mirror that reflects radio waves to a focus The age shows the 300 meter 1000 ft radio telescope in Arecibo The ALMA radio telescope interferometer is located in the Atacama desert north of Chile at an altitude of 5000 meters It has 66 antennas each 712 m diameters use as an interferometer to achieve a resolution about 5 times better than the Hubble telescope It works in the wavelength range from 03 to 966 mm 15 billion Infrared and Ultraviolet Telescopes SOFIA and Spitzer IR Infrared and ultraviolet Iigth telescopes operate like visiblelight telescopes but need to be high or above the atmosphere to see at these wavelengths UV telescopes were carried in Space Shuttle Missions ASTRO 1 and ASTRO 2 X Ray Telescopes XRay telescopes also need to be above the atmosphere Focusing of XRays requires special mirrors Thursday September 24 2015 Mirrors are arranged to focus XRay photons through grazing bounces off the sudace doubly reflected X rays second set of four nested mirrors focal Iane A first set of four nested mirrors Mirror elements are 08 m long and from 06 m to 12 m in diameter Gamma Ray Telescopes Gammaray telescopes also need to be in space Focusing gamma rays is extremely difficult How can multiple telescopes work together Interferometry Interferometry is a technique that consists of linking two or more telescopes and combining the signal from them What is the advantage The resolution obtained is equivalent to the resolution of a single large radio telescope of an equivalent diameter equal to the separation EX ALMA radio telescope VLA array in Socorro NM Easiest to do with radio telescopes because of the longer wavelengths Now possible with infrared and visiblelight telescopes Thursday September 24 2015 Future of Astronomy in Space The Moon would be an ideal observing site The lack of atmosphere makes it ideals for observing at almost all wavelengths radio UV IR X Ray and Gamma Rays Chapter 5 Earth and its Moon Earth Interior regions crust mantle and core Solid inner core about 1300 km Liquid outer core around 3500 km radius Atmosphere most located less than 50 km from surface It has a hydrosphere Magnetosphere area dominated by the terrestrial magnetic field Charged particles from the Sun are caught in Earth s magnetic field Moon No hydrosphere atmosphere or magnetosphere Some basic interior regions as Earth crust mantle and core but their properties are different Tides What are they and what causes them Review Every mass in the Universe has gravity associated with it Gravity is an attractive force Fgforce of gravity 1RA2 Force of gravity is inversely proportional to the distance The differential gravitational force and the tidal effect The differential gravitational force is the difference between the gravitational forces on the two sides of the body The force on the side facing the other body is stronger then the force of the opposite side Thursday September 24 2015 How does gravity cause tides Moon s gravity pulls harder on the near side of Earth than on the far side causing Earth to be displaced slightly toward the Moon Difference in Moon s gravitational pull stretches Earth Oceans are easy to be distorted This causes the Earth to experience a tidal bulge Variation in the Strength of the Tides The combined effects of the Sun and the Moon produce variations in high and low tides The Sun is about 375 times farther away than the Moon but its mass is much larger 20 X 10A3O kg compared with the moon 74 X 1022 kg A factor of 27 million in mass The Sun still has an effect in the tidal force on the Earth The tidal effect is smaller due to the small differential gravitational force Tides and Phases Size of tides on Earth depends on the phase of the Moon Spring tides occur at new and full moon The tidal forces of the Sun reinforce each other Neap tides occur first quarter and third quarter moon when the Sun and the Moon tidal forces act 90 degrees from each other The Earth develops two bulges A consequence of this is that every 24 hours there are two high tides and two low tides Tidal Locking The earth s rotation will slow down over a period of billions of years so that the orbital period of the Moon and the rotational period of the Earth will coincide Both periods will be synchronized of tidally locked Does the Sun have a tidal effect on the Earth The Sun has much more mass than a Moon The Sun s gravitational attraction on the Earth is larger than the Moon s gravitational attraction Thursday September 24 2015 But the Sun is much farther away than the Moon The Earth s Atmosphere lt shields from damaging solar and cosmic radiation Protects the surface Regulates temperature Composition 78 Nitrogen 21 Oxygen 09 Argon 003 Carbon Dioxide 01 O3 o Water Vapor The ionosphere is the layer above 80 km Part of the atoms are ionized by the solar UV radiation The Ozone is a molecule formed by three oxygen atoms Os Ozone absorbs UV light Convection occurs in the troposphere below 12 km which can cause weather Convection is when warmer air travels up and cooler air comes down to take its place The Greenhouse Effect Sunlight is not reflected by clouds reaches the Earth s surface Light reaching the Earth is absorbed to heat the surface The heated Earth reradiates this light in the form of infrared radiation blackbody radiation Infrared light is partially blocked by the Earth s carbon dioxide and water vapor content The two main greenhouse gasses in the terrestrial atmosphere are C02 and H20 vapor Only part of the IR light goes into space part is retained in the atmosphere Thursday September 24 2015 Why has Earth retained its atmosphere Gravity Gas molecules are in constant motion hotter gas faster motion The gas molecular velocity depends on the temperature higher temperatures higher velocities The fact that the atmosphere is heated keeps it from falling onto Earth Important concept Escape velocity is the speed an object or molecule has to have to be able to escape leave permanently a body s surface If a planet s escape velocity is at least 6 times greater tan the mean molecules velocity the molecules of that type will not escape in significant quantities Example Eanh Earth s escape velocity is 112 kms Oxygen and nitrogen molecular velocity is 06 kms The ratio of escape velocitymolecular velocity is 187 Oxygen may not escape the Earth s atmosphere Escape velocty 112 mass of body earth massesl radius of body Earth s radiusquot12 Avg molecular speed 0157 square root of Gas temperature in K W Global Warming The effect of the increase of abundance of carbon dioxide and the increase in the global temperature Burning fossil fuels increases the CO2 of the atmosphere Deforestation also decreases the absorption of CO2 An increase in the temperature will increase the melting of the polar ices positive feedback