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Astronomy 101 The Solar System Tuesday, Thursday Tom Burbine [email protected] Course • Course Website: – http://blogs.umass.edu/astron101-tburbine/ • Textbook: – Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. • You also will need a calculator. • There is an Astronomy Help Desk that is open Monday-Thursday evenings from 7-9 pm in Hasbrouck 205. • There is an open house at the Observatory every Thursday when it’s clear. Students should check the observatory website before going since the times may change as the semester progresses and the telescope may be down for repairs at times. The website is http://www.astro.umass.edu/~orchardhill/index.html. HWs #6, #7, and #8 • Due by Feb. 23rd at 1 pm News: Water on Enceladus (moon of Saturn) • The Cassini spacecraft found negatively charged water ions in the atmosphere • On Earth, such ions are often seen where liquid water is in motion, such as waterfalls or crashing ocean waves. / http://www.msnbc.msn.com/id/35313176/ns/technology_and_science-space Atoms make up molecules • H2O - water • CO2 – carbon dioxide • CH4 - methane Spectroscopy • Spectroscopy is the study of the interaction between radiation and matter as a function of wavelength (λ). • You can use spectroscopy to determine what is in a body (planet, star, etc.) or atmosphere http://upload.wikimedia.org/wikipedia/commons/f/f5/Light_dispersion_conceptual_waves.gif • How did scientists determined that there was water on the Moon? Water on the Moon Grey - H2O and OH absorptions White line - NASA' Cassini spacecraft Blue line - NASA's Moon Mineralogy Mapper instrument on the Indian Chandrayaan-1 spacecraft http://www.nasa.gov/images/content/388950main_ROGER_2-516.jpg Definitions • Reflectance – How much light an object reflects • Absorption – Light is absorbed and not reflected Light cause water molecules to vibrate • http://www.btinternet.com/~martin.chaplin/vibrat. html How much water? • If you had a cubic meter of lunar soil, you could squeeze it and get out a liter of water • Water has to be near the surface How do you use light to determine what is in an astronomical body like a star? What happens when electrons absorb energy? http://www.meditech.cn/images/pic9.jpg http://library.thinkquest.org/C006669/media/Chem/img/bohr.gif Energy levels where an electron can reside To go to a higher energy level, an electron needs to gain energy To go to a lower energy level, an electron needs to lose energy eV • 1 eV = 1.6 x 10-19 Joules Rules • An electron can not jump to a higher energy level unless it gains energy from somewhere else – Absorbs a photon – Gains kinetic energy from an impacting particle • To go to a lower energy level, the electron must lose energy – Emits a photon • Electron jumps can occur only with the particular amounts of energy representing differences between possible energy levels Heated hydrogen gas Emission line spectrum White light through cool hydrogen gas Absorption line spectrum Types of spectra • Emission – radiation is emitted at characteristic wavelengths – Material is “hot” so electrons keep on bumping into each other and transferring kinetic energy to each other so they jump between particular energy levels • Absorption – radiation is absorbed at characteristic wavelengths – Radiation passes through the material http://www.astro.bas.bg/~petrov/herter00_files/lec07_04.jpg So why is this important • Different elements have different number of electrons • Different elements have different energy levels for their electrons So • Different elements can absorb light at specific energies • Different elements can emit light at specific energies • So if you can measure the wavelength of the light from an astronomical body, you can determine whats in it Emission line spectra How can you determine velocities of objects? • Doppler Shift – The wavelength of light changes as the source moves towards or away from you • Since you know the wavelength position of emission or absorption features • If the positions of the features move in wavelength position, you know the source is moving So • Source moving towards you, wavelength decreases – blueshift • Source moving away from you, wavelength increases – redshift • http://www.youtube.com/watch?v=-t63xYSgmKE • http://www.youtube.com/watch?v=a3RfULw7aAY nanometer • 1 nanometer = 1 x 10-9 meters Blackbody • A black body is an object that absorbs all electromagnetic radiation that falls onto it. • Perfect emitter of radiation • Radiates energy at every wavelength http://www.daviddarling.info/images/blackbody.jpg • Stars and planets act can be modeled as blackbodies http://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpg • Stefan-Boltzman Law - The energy radiated by a blackbody per second per unit area is proportional to the fourth power of the temperature Energy emitted T4 s * m2 • Wien’s Law – There is an inverse relationship between the wavelength of the peak of the emission of a black body and its temperature Peak position 1/T • Stars and planets act can be modeled as blackbodies http://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpg Blackbody curves • http://www.mhhe.com/physsci/astronomy/applets/ Blackbody/frame.html http://www.rap.ucar.edu/general/asap-2005/Thur-AM2/Williams_DoD_Satellites_files/slide0005_image020.gif http://csep10.phys.utk.edu/astr162/lect/light/radiation.html Stefan Boltzman Law • For the same size object (same surface area), energy emitted per second is proportional to T4 • For example if a body goes from a temperature of 1,000 to 5,000 degrees Kelvin • How many times more energy is emitted per second from the hotter body? – Energy emitted per second (5000)4 = (5)4 = 625 times (1000)4 Power • Power is in Joules/second = Watts Stefan-Boltzman Law • Emitted power per square meter of surface = σT4 • Temperature in Kelvin • σ = 5.7 x 10-8 Watt/(m2*K4) • • • • For example, if the temperature of an object is 10,000 K Emitted power per square meter = 5.7 x 10-8 x (10,000)4 Emitted power per square meter = 5.7 x 10-8 x (1 x 1016) Emitted power per square meter = 5.7 x 108 W/m2 Wien’s Law • Wavelength of Maximum intensity of the blackbody curve peak = 2,900,000 nm T (Kelvin) • λmax = 2,900,000/10,000 nm • λmax = 290 nm • 1 nanometer = 1 x 10-9 meters • λmax = 290 nm = 2.0 x 10-7 meters New Rings around Saturn • • • • • • Seen in the infrared by the Spitzer Telescope Made of dust and ice; Dust is 80 Kelvin Lies some 13 million km from the planet Tilted 27 degrees from main ring plane 50 times more distant than the other rings and in a different plane. Probably made up of debris kicked off Saturn's moon Phoebe by small impacts. Why infrared for dust? • Cold things give off more light in infrared than visible When you observe an astronomical body • You measure intensity • Intensity – amount of radiation When you see an object in the sky • You measure its brightness • Its brightness is a function of its – Distance from Earth (can be calculated from orbit) If star: -Luminosity - is the amount of energy a body radiates per unit time If planet – Albedo – Size Inverse Square Law • The apparent brightness varies inversely by the square of the distance (1/d2) • If the Earth was moved to 10 Astronomical Units away, the Sun would be 1/100 times dimmer • If the Earth was moved to 100 Astronomical Units away, the Sun would be 1/10000 times dimmer If the Earth was moved to 1 x 108 Astronomical Units away, the Sun would be … A) 1 x 10-12 times dimmer B) 1 x 10-14 times dimmer C) 1 x 10-16 times dimmer D) 1 x 10-18 times dimmer E) 1 x 10-20 times dimmer If the Earth was moved to 1 x 108 Astronomical Units away, the Sun would be … A) 1 x 10-12 times dimmer B) 1 x 10-14 times dimmer C) 1 x 10-16 times dimmer D) 1 x 10-18 times dimmer E) 1 x 10-20 times dimmer Luminosity-Distance Formula • Apparent brightness = Luminosity 4 x (distance)2 Usually use units of Solar Luminosity LSun = 3.8 x 1026 Watts Magnitude System brightest asteroid 4 Vesta • Brighter –lower number http://www.astronomynotes.com/starprop/appmag.gif Magnitude difference Relative intensity 0 1 1 2 3 2.51 6.31 15.8 4 5 10 15 39.8 100 104 106 Initially • Everybody observed with their eyes Figure 7.1 Parallel light Figure 7.2a Lens Figure 7.2b Why are Telescopes better than your eyes? • They can observe light in different wavelength regions (eyes can only see visible light) • They can collect more light than eyes • They can be built to compensate for the distorting effects of the atmosphere Refracting telescope Figure 7.6 Reflecting Telescope Reflecting Telescopes Resulting image inverted All large modern telescopes are reflectors • Since light passes through the lens of a refracting telescope, • You need to make the lens from clear, highquality glass with precisely shaped surfaces It is • Its easier to make a high-quality mirror than a lens Also, • Large lenses are extremely heavy Also • Lens focuses red and blue light slightly differently • Called chromatic aberration http://en.wikipedia.org/wiki/File:Lens6a.svg Also • Light can be absorbed by the glass as it passes through the glass • Minor problem for visible, but severe for ultraviolet and infrared light Size of a telescope • Diameter of its primary mirror or lens • Light collecting area is proportional to the diameter squared since • Collecting area = r2 • E.g., 8-meter telescope a b • Telescope that took image b is twice as big as telescope that took image a • Larger the telescope, more detail can be seen • Telescope on Mauna Kea (14,000 feet high) • Telescope is Japanese Subaru 8-m telescope Atmosphere • Atmosphere can absorb light • Atmosphere can scatter light • Atmosphere can distort light (twinkling) Twinkling • Twinkling of stars is caused by moving air currents in the atmosphere. • The beam of light from a star passes through many regions of moving air while on its way to an observer’s eye or telescope. • Each atmospheric region distorts the light slightly for a fraction of a second. Advantages of space-based telescopes • • • • It can be open 24 hours, 7 days of week Do not have to worry about distorting effects of atmosphere There is no extra background of light due to scattering of light in the Earth’s atmosphere Observe in more wavelength regions Figure 7.20 http://www.scienzagiovane.unibo.it/English/radio-window/images/radiazioni-em.jpg • Infrared light absorbed by molecules http://www.ucar.edu/learn/1_3_1.htm Not all light from a star reaches Earth Light in space can be affected by dust http://www.ipac.caltech.edu/2mass/outreach/survey.html http://en.wikipedia.org/wiki/File:Rayleigh_sunlight_scattering.png It does not help • That you are closer to the stars To measure light • • • • In the past, they used photographic plates Now they use CCDs (charge-coupled devices) CCD are electronic detectors CCDs are chips of silicons Figure 7.5 CCDs • CCDs convert light into electrons Shared the 2009 Physics Nobel Prize for their discovery William Boyle George Smith How do they work? • The CCD is made up of pixels. • As the light falls on each pixel, the photons become electrons due to the photoelectric effect. The photoelectric effect happens when photons of light hit the silicon of the pixel and knock electrons out of place. • These electrons are then stored. • Essentially, the charge in each row is moved from one site to the next, a step at a time. This has been likened to a “bucket row” or human chain, passing buckets of water down a line. • As these buckets of electrons reach the end of the line they are dumped out and measured, and this analog measurement is then turned into a digital value. • Thus, a digital grid is made which describes the image. Color separation for digital cameras • Colored filters CCDs • CCDs can collect 90% of photons that strike them • Photographic plates can only collect 10% of the photons • CCDs are split into squares called pixels • Data is in electronic form Hubble Telescope • Can observe in visible, infrared, and ultraviolet wavelength regions • Named after Edwin Hubble, the father of modern cosmology Hubble (launched in 1990) Telescope is the size of a school bus 2.4 m mirror Initially • Hubble’s primary mirror was polished to the wrong shape • Was too flat at the edges • Was barely 2.3 micrometers out from the required shape (1/50 the width of a human hair) • Images were not focused as well as they could be • Later shuttle mission fixed this problem by installing a number of small mirrors http://dayton.hq.nasa.gov/IMAGES/SMALL/GPN-2002-000064.jpg Jupiter • http://video.nationalgeographic.com/video/player/ science/space-sci/exploration/hubble-sci.html Hubble replacement • The first major components of the new James Webb Space Telescope are now being assembled. • While Hubble is the size of a bus, the new James Webb will be the size of a jetliner. • Will launch in 2014 • James Webb is a former NASA administrator during the Apollo program • http://www.youtube.com/watch?v=SpkrVw_E6N w Any Questions?