SIMG-217 Fundamentals of Astronomical Imaging Instructor: Joel Kastner Office: 1

SIMG-217 Fundamentals of Astronomical Imaging Instructor: Joel Kastner Office: 1

SIMG-217 Fundamentals of Astronomical Imaging Instructor: Joel Kastner Office: 1

Younger, Carolyn, Features Reporter has reference to this Academic Journal, PHwiki organized this Journal SIMG-217 Fundamentals of Astronomical Imaging Instructor: Joel Kastner Office: 17-3190 Phone: 475-7179 Email: Course Description Familiarizes students with the goals in addition to techniques of astronomical imaging. The broad nature of astronomical sources will be outlined in terms of requirements on astronomical imaging systems. These requirements are then investigated in the context of the astronomical imaging chain. Imaging chains in the optical, infrared, X-ray, in addition to /or radio wavelength regimes will be studied in detail as time permits. (prerequisite: 1051-215 or permission of instructor) Laboratories 3 m in addition to atory experiments, selected from: Star Colors from Digital Images Spectroscopic Imaging of Gases Multiwavelength Imaging of the Sun Multiwavelength Imaging of the Orion Nebula Final Project; one of: collect/process images taken at RIT observatory (weather, time permitting) detailed followup of one of the above lab experiences Student-proposed project/investigation in astronomical imaging

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Topics Review of Imaging Systems Issues in Astronomical Imaging Systems History of Astronomical Imaging Systems Contemporary Astronomical Imaging Systems What does the future hold as long as astronomical imaging Goal of Imaging Systems Create an “image” of a scene that may be measured to calculate some parameter of the scene Diagnostic X ray Digital Photograph “CAT” Scan (computed tomography) “MRI” (magnetic resonance imaging) Imaging Systems “Chain” of stages One possible (in fact, common) sequence: Object/Source Collector (lens in addition to /or mirror) Sensor Image Processing (computer or eye-brain) Display

Issues in Astronomical Imaging Distances between objects in addition to Earth Intrinsic “brightness” of object generally very faint large image collectors large range of brightness (dynamic range) Type of energy emitted/absorbed/reflected by the object wavelength regions Other considerations: motion of object brightness variations of object Astronomical Imaging: Overview When you think of a clear, dark night sky, what do you visualize The human visual system is fine-tuned to focus, detect, in addition to process (i.e., create an “image” of) the particular wavelengths where the Sun emits most of its energy evolutionary outcome we see best in the dominant available b in addition to of wavelengths As a result, when we look at the night sky, what we see is dominated by starlight (like the sun) We think of stars in addition to planets when we think of astronomy History of Astronomical Imaging Systems Oldest Instruments, circa 1000 CE – 1600 CE Used to measure angles in addition to positions Included No Optics Astrolabe Octant, Sextant Tycho Brahe’s Mural Quadrant (1576) Star Catalog accurate to 1′ (1 arcminute, limit of human resolution) Astronomical Observatories as part of European Cathedrals

Mural Quadrant Observations used by Johannes Kepler to derive the three laws of planetary motion Laws 1,2 published in 1609 Third Law in 1619 H.C. King, History of the Telescope History of Astronomical Imaging Systems Optical Instruments, (1610+) Refracting Telescope Galileo Lippershey Hevelius Reflecting Telescope Newton (ca 1671) Spectroscope Newton Hevelius’ Refractor ca. 1650 Lenses with very long focal lengths – WHY to minimize “induced color” (“chromatic aberration”) due to variation in refractive index with wavelength H.C. King, History of the Telescope

Optical Dispersion n Optical Dispersion “Refractive Index” n measures the velocity of light in matter c = velocity in vacuum 3 108 meters/second v = velocity in medium measured in same units n 1.0 Optical Dispersion Refractive index n of glass tends to DECREASE with increasing wavelength focal length f of lens tends to INCREASE with increasing wavelength Different colors “focus” at different distances “Chromatic Aberration”

Chromatic Aberration Newton’s Reflector ca. 1671 1″-diameter mirror no chromatic aberration from mirror! H.C. King, History of the Telescope Reflection from Concave Mirror All colors “focus” at same distance f f

Larger Reflecting Telescopes Lord Rosse’s 1.8 m (6′-diameter) metal mirror, 1845 H.C. King, History of the Telescope History of Astronomical Imaging Systems Image Recording Systems Chemical-based Photography wet plates, 1850 + dry plates, 1880+ Kodak plates, 1900+ Physics-based Photography, 1970 + Electronic Sensors, CCDs Electromagnetic Spectrum

History of Astronomical Imaging Systems Infrared Wavelengths (IR) Longer waves than visible light conveys in as long as mation about temperature images “heat” Absorbed by water vapor in atmosphere Courtesy of Inframetrics History of Astronomical Imaging Systems Infrared Astronomy Wavelengths are longer than as long as visible light IR wavelengths range from ~1 micron to ~200 microns Over major portions of this range, IR is absorbed by water vapor in atmosphere Infrared Astronomy Because infrared light is generated by any “warm” objects, detector must be cooled to a lower temperature Uncooled detector is analogous to camera with an internal light source camera itself generates a signal Cooling is a BIG issue in Infrared Astronomy

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History of Astronomical Imaging Systems History of Astronomical Infrared Imaging 1856: using thermocouples in addition to telescopes (“one-pixel sensors”) 1900+: IR measurements of planets 1960s: IR survey of sky (Mt. Wilson, single pix detector) 1983: IRAS (Infrared Astronomical Satellite) 1989: COBE (Cosmic Background Explorer) History of Astronomical Imaging Systems: Infrared Astronomy Airborne Observatories Galileo I (Convair 990), 1965 – 4/12/1973 (crashed) Frank Low, 12″–diameter telescope on NASA Learjet, 1968 Kuiper Airborne Observatory (KAO) (36″–diameter telescope) Stratospheric Observatory as long as IR Astronomy (under development: 2.4-meter diameter telescope on 747) Spaceborne Observatories “Orbiting Astronomical Observatory” (OAO), 1960s “Infrared Astronomical Satellite” (IRAS), 1980s Hubble Space Telescope (HST), 1990 (some IR astronomy) Infrared Satellite Observatory (ISO), 1995-1998 Spitzer Space Telescope (Aug. 2003-present) Kuiper Airborne Observatory Modified C-141 Starlifter 2/1974 – 10/1995 ceiling of 41,000′ is above 99% of water vapor, which absorbs most infrared radiation

Infrared Images Visible Near Infrared Far Infrared 2Mass ISO History of Astronomical Imaging Systems: Radio Astronomy Radio Waves Wavelengths are much longer than visible light millimeters ( in addition to longer) vs. hundreds of nanometers Selective History 1932: Karl Jansky (Bell Telephone Labs) investigated use of “short waves” as long as transatlantic telephone communication 1950s: Plans as long as 600-foot “Dish” in Sugar Grove, WV ( as long as receiving Russian telemetry reflected from Moon) 1963: Penzias in addition to Wilson (Bell Telephone Labs), “Cosmic Microwave Background” 1980: “Very Large Array” = VLA, New Mexico Jansky Radio Telescope Image courtesy of NRAO/AUI

Telescope Tracking Axis of Rotation Polaris Proper Motion of Astronomical Objects “real” relative motion of object “proper motion” generally VERY small except as long as nearby objects Moon: 360º in 1 month 12º per day ½º per hour Moon moves its own diameter in the sky in about one hour Determines lengths of phases of eclipses Proper motions of Asteroids in addition to Comets can be large must be “tracked” to take long-exposure images Apparent proper motions of planets are quite small Apparent proper motions of stars (even nearby stars) are very small – but still very measurable!

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