Published on February 12, 2009
Optical Telescopes LACC: § 5.1, 4, 5 • Optical Telescopes: Refracting vs. Reﬂecting • Reﬂecting Telescopes: prime vs. Cassegrain vs. Newtonian vs. Coudé • Q: Why make telescopes so big? Telescope technology is primarily about detecting objects that are normally too dim or outside the range of human vision. Thursday, February 18, 2010 1
Optical Telescopes Refracting * Primary Lens * Reﬂecting * Primary Mirror * Catadioptric * Both * http://www.meade.com/support/telewrk.html Thursday, February 18, 2010 2
Reﬂecting Telescopes http://188.8.131.52/astronomy/Chaisson/AT405/HTML/AT40501.htm Thursday, February 18, 2010 3
Why Make Telescopes Big? James Webb Space Telescope Areacircle = π•radius2 (JWST) So, a telescope with twice the diameter (or radius) will have four times the light collecting area. 10x the diameter would mean 100x the light collecting area. http://www.jwst.nasa.gov/comparison.html Thursday, February 18, 2010 4
Why Make Telescopes Big? "Angular resolution" = smallest angular separation where you can still see that 2 objects are actually 2 objects rather than 1 blobby object • The human eye's angular resolution = 1 arcminute • The Hubble Space Telescope's ang. resolution = 0.05 arcseconds http://www.physast.uga.edu/~rls/astro1020/ch7/ovhd.html Thursday, February 18, 2010 5
Adaptive Optics Temperature ﬂuctuations in Earth's atmosphere act like small, randomly sized and oriented weak lenses that cause stellar images to degrade and dance (twinkle), limiting the resolution and sensitivity of ground-based telescopes. "Seeing," as these effects are called, varies with the site and conditions but never vanishes. The only way to avoid it is to launch a telescope into space. Mauna Kea and, to a lesser extent, Haleakala have better seeing than most observatory locations, yet even at these exceptional sites, the atmosphere Adaptive Optics (AO) System: The deformable mirror turns pinpoint sources of light changes shape to remove the distortions in the lightwave (such as stars) into slightly fuzzy before the light goes to the camera. blobs. http://www2.ifa.hawaii.edu/newsletters/article.cfm?a=300&n=1 Thursday, February 18, 2010 6
Optical Telescopes LACC: § 5.1, 4, 5 • Optical Telescopes: Refracting vs. Reﬂecting • Reﬂecting Telescopes: prime vs. Cassegrain vs. Newtonian vs. Coudé • Q: Why make telescopes so big? A: Light Gathering Power Angular Resolution (alternatives-- Interferometry, Adaptive Optics) Telescope technology is primarily about detecting objects that are normally too dim or outside the range of human vision. Thursday, February 18, 2010 7
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 5, pp. 131-132: 3. Give two reasons. Due at the beginning of the next class period. Test covering chapters 1-5 next class period. Thursday, February 18, 2010 8
Observing the Entire EM Spectrum LACC: § 5.1, 4, 5 • Telescopes: Designs • Our Atmosphere: Optical (Infrared) and Radio Atmospheric Windows • Space: Interstellar Dust is Transparent to Infrared and Radio Telescope technology is primarily about detecting objects that are normally too dim or outside the range of human vision. Thursday, February 18, 2010 9
The EM Spectrum • Credit: Philip Ronan who has given permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version. • Download site: Wikipedia: Image:EM spectrum.svg. http://www.nhn.ou.edu/~jeffery/course/c_energy/energyl/lec001.html Thursday, February 18, 2010 10
EM Rad. & Earth’s Atmosphere http://www.answers.com/topic/telescope?cat=technology Thursday, February 18, 2010 11
Radio Telescopes All radio telescopes are ground based. Why? http://www.skyscan.ca/RadioTelescopes.htm Thursday, February 18, 2010 12
Radio image Shells of ancient supernovas, cocoons surrounding newborn stars, and specks from distant quasars highlight this tremendous vista.... The representative color image covers about 10 degrees across on the sky ... in radio light. Diffuse bands of ionized gas ﬂow though a dominating region of star formation, located about 6000 light-years away. Two prominent supernova shells visible include the brown globule on the lower left and the white bumpy sphere on the upper right. Prominent stellar cocoons are visible throughout the image as bright white knots. Far in the distance, visible here as only red dots, quasars glow. http://antwrp.gsfc.nasa.gov/apod/ap020218.html Thursday, February 18, 2010 13
Interferometry Powerful arrays of telescopes, like the Very Large Array (VLA) in New Mexico, can be coordinated in such a way as to "see" radio sources and having the effect of a single dish nearly 20 miles across. http://www.geocities.com/plasminojen/astro/radio_astronomy.html Thursday, February 18, 2010 14
Infrared Telescopes NASA's Stratospheric Observatory for Infrared Astronomy Earth’s atmosphere blocks much of the infrared radiation that comes from space. Placing telescopes in orbit overcomes this problem; but for infrared astronomy, it’s not absolutely http://www.skyscan.ca/RadioTelescopes.htm necessary. Thursday, February 18, 2010 15
Infrared Telescopes The Wide-ﬁeld Infrared Survey Explorer (WISE) is the latest moon shown for scale visible light infra red http://photojournal.jpl.nasa.gov/catalog/PIA12832 http:// antwrp.gsfc.nasa.gov/ apod/ap061228.html http://www.sciencenewsforkids.org/ articles/20100106/Note3.asp Thursday, February 18, 2010 16
Visible vs. Infrared Warm dust becomes visible when viewed in the ir. (So ir telescopes must be cooled.) Remember: interstellar dust blocks visible light, but not ir. http://www.spitzer.caltech.edu/Media/happenings/20051208/ Thursday, February 18, 2010 17
X-Ray Telescopes Earth’s atmosphere blocks the x-ray radiation that comes from space. For this reason, all x-ray telescopes are placed in orbit. http://www.geocities.com/wt2002friendz/schoolwork/telescope_gina_mei.html Thursday, February 18, 2010 18
X-Ray Image Spanning over 25,000 light-years, comparable to the distance from the Sun to the center of our own Milky Way galaxy, a cosmic jet seen in X-rays blasts from the center of Centaurus A. Only 10 million light-years away, Centaurus A is a giant elliptical galaxy - the closest active galaxy to Earth. This composite image illustrates the jumble of gas, dust, and stars visible in an optical picture of Cen A superposed on a new image recorded by the orbiting Chandra X-ray Observatory. The X- ray data is shown in red. Present theories hold that the X-ray bright jet is caused by electrons driven to extremely high energies over enormous distances. The jet's power source is likely to be a black hole with about 10 million times the mass of the Sun coincident with the X-ray bright spot at the galaxy's center. http://apod.nasa.gov/apod/ap991028.html Thursday, February 18, 2010 19
Gamma Ray Telescopes Solid state gamma ray detectors in space or optical reﬂecting telescopes to detect evidence of air showers. http://imagine.gsfc.nasa.gov/docs/science/how_l2/gamma_detectors.html Thursday, February 18, 2010 20
Gamma Ray Image Top: High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in South-West Africa. This system of four 13 m diameter telescopes is currently the most sensitive detector of very high energy gamma-rays. Center: A larger picture of the gamma ray sky as measured with H.E.S.S. Bottom Left: The green star shows the position of LS5039 as measured using radio telescopes, and the white ellipse shows the gamma ray position. In the upper-left corner ... HESS J1825-137. Bottom Right: A computer simulation of the microquasar LS5039, showing one possible scenario where gamma rays are generated in microquasar 'jets'. http://www.mpi-hd.mpg.de/hfm/HESS/pages/press/old/PressRelease/ LS5039Press-2005/LS5039_Press_E.htm Thursday, February 18, 2010 21
Observing the Entire EM Spectrum LACC: § 5.1, 4, 5 • Telescopes: Designs requirements for: radio, infrared, visible/uv, x-ray, gamma ray • Our Atmosphere: Optical (Infrared) and Radio Atmospheric Windows • Space: Interstellar Dust is Transparent to Infrared and Radio Telescope technology is primarily about detecting objects that are normally too dim or outside the range of human vision. Thursday, February 18, 2010 22
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 5, pp. 131-132: 7. The different regions of the spectrum are: radio, microwave, infrared, visible, ultraviolet, x-ray, gamma ray. Due at the beginning of the next class period. Test covering chapters 1-5 next class period. Thursday, February 18, 2010 23
Review for the Test 1 of 5: Observational Astronomy [10 pts] The History of Astronomy • shape (Aristotle) and size (Eratosthenes) and of the [10 pts] Telescopes Earth • Understand how the different kinds of optical • Geocentric (Ptolemy) vs. Heliocentric telescopes work: refracting vs reflecting--prime, (Copernicus), Galileo Cassegrain, Newtonian, Coudé; and non-optical • Kepler (3 Laws or Planetary Motion), Newton (3 telescopes: radio, infrared, X-ray, gamma ray Laws of Gravity, Universal Gravity) • Understand how the Earth’s atmosphere affects observations (atmospheric windows--visible, radio) [10 pts] Making use of the Heavens and telescope design (which ones can’t be ground • Know the Celestial Sphere: RA, Dec, meridian, based--gamma ray, X-ray, ultraviolet) zenith, N/S Poles, Celestial Equator • Understand how telescopes are built to improve • Understand how the 23.5° axial tilt of the Earth their light gathering ability and angular resolution affects the motion/position of celestial objects: (large primary mirrors, adaptive optics, Arctic/Antarctic Circle, Tropic of Cancer/Capricorn interferometry) • Know how the heavens can be used to mark time: moon phases, eclipses, solar/sidereal day [10 pts] Figures/Illustrations • Understand orbital mechanics and moon phases [10 pts] Electromagnetic Radiation • Use a graphic showing the energy levels around an • Understand how energy, frequency, and wavelength atom to determine what photon energies could be relate to each other: v = f λ, E=hf absorbed/emitted; ID elements in a spectrum • Know the order of the electromagnetic spectrum: • ID the type of telescope (refracting; reflecting-- radio, microwave, ir, visible, uv, x-ray, gamma ray prime, Cassegrain, Newtonian, Coudé, radio, • Know how photon interact with atoms: energy infrared, X-ray, gamma ray) or spectra (continuous/ levels, types of spectra--continuous, absorption, thermal, emission line, absorption line) from a emission line picture Thursday, February 18, 2010 24
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