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. 1 Thursday, February 18, 2010
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Optical TelescopesLACC: § 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
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.
"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
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 turns pinpoint sources of light (such as stars) into slightly fuzzy blobs.
Adaptive Optics (AO) System: The deformable mirror changes shape to remove the distortions in the lightwave
• 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.
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.
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.
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
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'.
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.
23Thursday, February 18, 2010
Review for the Test 1 of 5:Observational Astronomy
[10 pts] The History of Astronomy• shape (Aristotle) and size (Eratosthenes) and of the
Earth• Geocentric (Ptolemy) vs. Heliocentric
(Copernicus), Galileo• Kepler (3 Laws or Planetary Motion), Newton (3
Laws of Gravity, Universal Gravity)
[10 pts] Making use of the Heavens• Know the Celestial Sphere: RA, Dec, meridian,
zenith, N/S Poles, Celestial Equator• Understand how the 23.5° axial tilt of the Earth
affects the motion/position of celestial objects: Arctic/Antarctic Circle, Tropic of Cancer/Capricorn
• Know how the heavens can be used to mark time: moon phases, eclipses, solar/sidereal day
[10 pts] Electromagnetic Radiation • Understand how energy, frequency, and wavelength
relate to each other: v = f λ, E=hf• Know the order of the electromagnetic spectrum:
radio, microwave, ir, visible, uv, x-ray, gamma ray• Know how photon interact with atoms: energy
levels, types of spectra--continuous, absorption, emission line
[10 pts] Telescopes• Understand how the different kinds of optical
telescopes work: refracting vs reflecting--prime, Cassegrain, Newtonian, Coudé; and non-optical telescopes: radio, infrared, X-ray, gamma ray
• Understand how the Earth’s atmosphere affects observations (atmospheric windows--visible, radio) and telescope design (which ones can’t be ground based--gamma ray, X-ray, ultraviolet)
• Understand how telescopes are built to improve their light gathering ability and angular resolution (large primary mirrors, adaptive optics, interferometry)
[10 pts] Figures/Illustrations• Understand orbital mechanics and moon phases• Use a graphic showing the energy levels around an
atom to determine what photon energies could be absorbed/emitted; ID elements in a spectrum
• ID the type of telescope (refracting; reflecting--prime, Cassegrain, Newtonian, Coudé, radio, infrared, X-ray, gamma ray) or spectra (continuous/thermal, emission line, absorption line) from a picture