Rosetta “lands” on Comet 67P/C-GCourse AnnouncementsAssignmentsA Problem of the AtmosphereSeeingSolving the problem of SeeingActive OpticsAdaptive OpticsAdaptive OpticsMost Advanced AO v. HubbleRadio AstronomyRadio AstronomyArecibo TelescopeRequired Dish SmoothnessValue of Radio AstronomyBehind the VeilInterferometryInterferometry – Combining SignalsRadio Interferometer ResolutionInterferometry at other WavelengthsSpace-Based AstronomySpace-Based Astronomy - IRSpace-Based Astronomy - IRSpace-Based Astronomy - IRSpace-Based Astronomy - MicrowavesSpace-Based Astronomy - MicrowavesThe Microwave GalaxyUltraviolet AstronomyUltraviolet AstronomyUltraviolet AstronomyUltraviolet AstronomyHigh-Energy AstronomyX-ray Telescope DesignChandra X-ray ObservatoryGamma Ray AstronomyGamma Ray AstronomyGamma Ray AstronomyMulti-wavelength Milky WayFull Spectrum CoverageRosetta “lands” on Comet 67P/C-GCredit: ESA/Rosetta/MPS/OSIRIS TeamFinal Descent on 30 September, 20165.8 km above surfaceImage measures about 225 m acrossImage Scale is about 11 cm/pixelCourse Announcements•Exam 1 grading underway–Expected return date: Wednesday, 5 Oct.•Current scores will go on Blackboard as I finish grading the examsAssignmentsReading Assignments•No new readingParallel Lectures•CC Astronomy: Episode 6 - TelescopesMastering Astronomy•Chapter 5 Homework[Due Tuesday, 4 Oct. at 11:59 PM EDT]A Problem of the AtmosphereAtmospheric Blurring, a.k.a. SEEING due to air movementsSeeing, or angular resolution of blurring is typically 1 arcsecondCredit: Michael RichmondMoving pockets of air, with different densities, act like lenses making it so light rays don’t focus perfectlySeeing•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 observationsBlurring of images due to air movements blurring the imageCredit: Alan AdlerBinary star imaged 5 times at 2 minute intervalsChanges are due to Atmospheric distortionsCrater on the MoonSolving the problem of Seeing1. Put telescopes at high altitude (above as much atmosphere as possible) in dry, clean-air places1. Also avoids that Light-Pollution2. Put telescopes in space3. Use fancy technology to correct for atmospheric blurring -> Active and Adaptive OpticsGet above as much atmosphere as possible!Active Optics•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 mCorrects for deformations in the mirrorStar Cluster R136 without active opticsBoth Images taken with New Technology Telescope (ESO)Star Cluster R136 with active opticsAngular Resolution is about 0.2”Adaptive Optics•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 computersCorrects for atmospheric blurring in real-timeLaser Guide Star on the Very Large Telescope (VLT) arraypew pew pewAdaptive Optics•Gets angular resolutions as low as 0.063” which is near the diffraction limit of an 8 meter telescope at a wavelength of 1 µmDiff. Limit = 0.25*(1µm/8m) = 0.03”•Requires very powerful computers and out most advanced telescope engineeringCorrects for atmospheric blurring in real-timeMost Advanced AO v. HubbleGaliean Moons as seen by HubbleGround based Image:VLT + IRDIS (2.1 µm) - Extreme AO.L. Fletcher, N. Thatte, K. Donaldson Hanna, S. Lindsay, N. BowlesRadio Astronomy•Prime focus reflecting telescope design•Given radio waves’ long wavelengths, radio telescopes have severe resolution challenges!Reflecting long wavelengths“proportional to”Radio wavelengths are approximately 100,000 - 1 million times longer than visible!Radio AstronomyGreenbank Radio Telescope•105 m National Radio Astronomy Observatory•Largest steerable single dish radio telescope•Most sensitive to 1 cm wavelength radiation -> Ang. Resolution = 20 arcsecArecibo TelescopeLargest Single Dish TelescopeDiameter = 305 m => Ang. Res. at 10cm of 82 arcsec Not steerableOperates at 3 cm to 1 meter wavelengthsChina is currently building a 500m single dish radio telescopeRequired Dish Smoothness•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 mmLonger wavelength light does not required as smooth of a surface to preserve reflectionsValue of Radio Astronomy•Can operate during the daylight•Can operate in cloudy conditions, rain, snow, etc.–24 hours of operationNew 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 universeNew view without diurnal limitationsBehind the Veil•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 VisibleRight: 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)Radio astronomy can pierce through the dust in the universe Visible (NTT) and Radio (ALMA) ImageCredit: ESO/NTT/ALMAInterferometry •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 telescopesLinking telescopes together to increase angular resolution The Very Large Array (VLA) – 27 25-m scopes over 30 kmNew MexicoThe Atacama Large Millimeter Array(ALMA). 66 12-m scopesInterferometry – Combining 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 dishesCombining radio signalsThis angle
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