Rosetta lands on Comet 67P C G Final Descent on 30 September 2016 5 8 km above surface Image measures about 225 m across Image Scale is about 11 cm pixel Credit ESA Rosetta MPS OSIRIS Team Course Announcements Exam 1 grading underway Expected return date Wednesday 5 Oct Current scores will go on Blackboard as I finish grading the exams Assignments Reading Assignments No new reading Parallel Lectures CC Astronomy Episode 6 Telescopes Mastering Astronomy Chapter 5 Homework Due Tuesday 4 Oct at 11 59 PM EDT A Problem of the Atmosphere Atmospheric Blurring a k a SEEING due to air movements Moving pockets of air with different densities act like lenses making it so light rays don t focus perfectly Credit Michael Richmond Seeing or angular resolution of blurring is typically 1 arcsecond Seeing Blurring of images due to air movements blurring the image Turbulence and eddies in Earth s atmosphere refract bend as they swirl about Pockets of air act like lenses Affects shorter wavelengths more severely Most correction methods are done for infrared Crater on the Moon observations Binary star imaged 5 times at 2 minute intervals Changes are due to Atmospheric distortions Credit Alan Adler Solving the problem of Seeing Get above as much atmosphere as possible 1 Put telescopes at high altitude above as much atmosphere as possible in dry clean air places 1 Also avoids that Light Pollution 2 Put telescopes in space 3 Use fancy technology to correct for atmospheric blurring Active and Adaptive Optics Active Optics Corrects for deformations in the mirror Deformations due to changing environmental conditions e g thermal expansion contraction Actively adapts mirror shape with actuators on an inserted correction mirror Invention allowed for telescopes larger than 8 m Star Cluster R136 without active optics Star Cluster R136 with active optics Both Images taken with New Technology Telescope ESO Angular Resolution is about 0 2 Adaptive Optics Corrects for atmospheric blurring in real time Laser Guide Star on the Very Large Telescope VLT array w pe w pe w pe Uses a guide star or creates an artificial one with a laser to measure atmospheric disturbance in real time Requires more mirrors Requires fast powerful computers Adaptive Optics Corrects for atmospheric blurring in real time Gets angular resolutions as low as 0 063 which is near the diffraction limit of an 8 meter telescope at a wavelength of 1 m Diff Limit 0 25 1 m 8m 0 03 Requires very powerful computers and out most advanced telescope engineering Most Advanced AO v Hubble Galiean Moons as seen by Hubble Ground based Image VLT IRDIS 2 1 m Extreme AO L Fletcher N Thatte K Donaldson Hanna S Lindsay N Bowles Radio Astronomy Reflecting long wavelengths Prime focus reflecting telescope design Given radio waves long wavelengths radio telescopes have severe resolution challenges proportional to Radio wavelengths are approximately 100 000 1 million times longer than visible Radio Astronomy Greenbank Radio Telescope 105 m National Radio Astronomy Observatory Largest steerable single dish radio telescope Most sensitive to 1 cm wavelength radiation Ang Resolution 20 arcsec Arecibo Telescope Largest Single Dish Telescope Diameter 305 m Ang Res at 10cm of 82 arcsec Not steerable Operates at 3 cm to 1 meter wavelengths China is currently building a 500m single dish radio telescope Required Dish Smoothness Longer wavelength light does not required as smooth of a surface to preserve reflections Surface irregularities must be much smaller than the wavelength of light Difficult for Optical Telescopes wavelength is few 100s of nm Much easier for Radio telescopes wavelengths of few cm to m Chicken wire supplied sufficient smoothness for original Arecibo surface Now uses thin metal panels that maintain spherical shape with an accuracy of about 3 mm Value of Radio Astronomy New view without diurnal limitations Can operate during the daylight Can operate in cloudy conditions rain snow etc 24 hours of operation New View of the Universe Can see objects that do not emit much visible light Cold objects Travels through interstellar dust Different wavelengths different information e g rotational molecular lines are radio wavelengths so great at detecting the molecular universe Behind the Veil Radio astronomy can pierce through the dust in the universe Radio waves pass through the dust that visible light is blocked by Allows us to see what is obscured by the dust Complimentary information between Radio and Visible Right Image of a new star being born The visible light is blocked by the dust but radio waves allow us to see the forming star and its radio jets Herbig Haro Objects H46 H47 Visible NTT and Radio ALMA Image Credit ESO NTT ALMA Interferometry Linking telescopes together to increase angular resolution Combines the signals of several widely spaced telescopes together as if it came from a single dish Resolution will be equivalent to a single telescope with diameter equal the largest separation between the linked telescopes The Very Large Array VLA 27 25 m scopes over 30 km New Mexico The Atacama Large Millimeter Array ALMA 66 12 m scopes Interferometry Combining Signals Combining radio signals Interferometry combines the signals of two or more telescopes by exploiting the interference of waves Effectively increases the diameter and hence angular resolution of the telescope to be the distance between the two farthest dishes This angle is really really really small Radio Interferometer Resolution Use of large radio telescope arrays can give angular resolution comparable to that of an optical telescope BOTH The colliding Antennae Galaxies TOP ALMA Atacama Large Millimeter Array image radiograph in false color with resolution of few arcsec BOTTOM Hubble image of same galaxy sub arcsec resolution Interferometry at other Wavelengths The shorter the wavelength the more difficult to combine the signals Infrared Keck Telescopes Very Large Telescope VLT Array Optical Center for High Angular Resolution Astronomy CHARA Six 1 m optical telescopes with effective baseline of 300m Angular Resolution 0 0002 Space Based Astronomy Most wavelengths require being outside of Earth s obscuring atmosphere Atmospheric Opacity How much is the atmosphere like a window or like a wall 100 Opacity Wall Space required 0 Opacity Window Ground okay Gamma Ray X ray UV Microwave Radio Visible Near IR Mid far IR Long Radio Space Based Astronomy IR Short wavelength Infrared radiation can penetrate dusty
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