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Telescopes−January 31 • • First test is next Wed Covers atoms & light. Does not cover telescopes. Practice test on angel. “Missouri Club” (Show me) • Mon, 31 Jan, 7:008:00pm, 1415 BPS (next door) • Atoms emit and absorb light (left over from Fri) Telescopes a. b. c. d. Formation of spectral lines [see Fig 5.7] Individual atoms Incoming Lyα photons from star 3. The spectrum of the outer parts of a planetary nebula is very different from that of a black body because the planetary nebula is Energy è • • • • very hot very cool not black black Stars vs. Gas Clouds Continuum Spectrum [Fig. 5.9] Photospheres of stars Single incoming Lyα photon excitation followed by de-excitation The Sun’s photosphere) Lyα photon emitted in random direction s ee rs ve n r e s o Ob issi em es lin Outer, cooler layers Absorption Spectrum Emission spectrum: Planetary nebula shell Observer sees absorption lines Incoming photons of all wavelengths from star Lyα photons, emitted in lots of random directions 1 Telescopes [5.3] Some large ground-based optical telescopes Twin Keck 10m (400”) reflectors Mauna Kea, 1993 Galileo’s telescopes: ~1” in diameter x 24-30” long • Magnify images è see details • Gather light over large surface area è see fainter objects. Lick 36” Refractor 1888 Mt. Palomar 200” Reflector 1948 Light-gathering power: ∝ (mirror area) ∝ (mirror diameter)2 Technological advances: Using a lens (refractor) Using a mirror (reflector) The SOAR • Lenses è mirrors. Europe’s Very Large • Thick mirrors è thin mirrors. Telescope (Four 8m telescopes) passive è active support. • Improved image quality. Mirror for Gemini 8m Telescope • Now working on designs for 30m diameter telescopes. An International Partnership 4m Telescope National Optical Astronomy Observatory Brazil Cerro Pachón, Chile MSU’s Window on the Universe 2 Why the southern hemisphere? Michigan Michigan CHILE CHILE Small Magellanic Cloud Large Magellanic Cloud Remote Observing from MSU Center of Milky Way The View from Chile 3-mirror optical path The Telescope inside the Dome M2 M3 Fast tip-tilt Primary Mirror Primary Mirror 14 feet diameter 4 inches thick M1 Primary Mirror Instrument (analyzes light) 3 Telescopes carry many different instruments to analyze light. Must maintain mirror shape to 0.000001 inches. SOAR’s instruments: Primary Mirror • • • • Primary Mirror 14 feet diameter 4 inches thick Optical spectrographs (2). Infrared spectrographs (2). Optical imager. Infrared imager. The Spartan Infrared Camera 120 computer-controlled force actuators. Tip-tilt Correction of Atmospheric Turbulence Spartan Infrared Camera High Resolution Imaging for the SOAR Telescope www.pa.msu.edu/~loh/SpartanIRCamera • The Spartan Infrared Camera is a $2.0M instrument funded by MSU, Brazil, SOAR, and the National Science Foundation. • Primary technical goal: • Imaging with high angular resolution in the near infrared (1000-2500 nm) where • Tip-tilt correction of atmospheric turbulence produces sharpest images. • Primary science goal for infrared: • Observe distant galaxies & supernovae • Center of Milky Way galaxy • Designed and built by the MSU Physics-Astronomy Dept. • Tip-tilt correction • Method: • Sense the position of a bright star • Move a mirror 60 times per second to keep bright star centered • Why use tip-tilt correction? Tip-tilt Without tip-tilt 1 0.5 0 -0.5 -1 -0.5 0 0.5 1 1.5 1 1.5 1 0.5 • • • • Simulated image of a double star. Where is the double star? Where is the fainter companion star? In image with 10 & 1000 the exposure time • Do you see the companion? • Is the companion visible with natural seeing? • With tip-tilt correction • Detail become visible • Fainter stars become visible 0 -0.5 10 times exposure -1 -0.5 0 0.5 1 0.5 0 -0.5 100 times exposure -1 -0.5 0 0.5 1 1.5 4 Very Large Array Radio telescopes Angular resolution = Radio Telescope in New Mexico wavelength mirror diameter • Radio wavelengths are large è need large mirror diameter to see smallangle details. Array of smaller telescopes simulates a huge aperture. • Arecibo, Puerto Rico…. • 1000 ft. diameter, but same angular resolution as 0.01 ft optical telescope. Radio galaxy Cygnus A Key parameters of telescopes • Fainter objects are visible with a larger telescope because • • 1. The primary motivation for the VLA is a. b. c. 2. R1: a larger telescope collects more light. R2: with the sharper images of a larger telescope, the light is more concentrated. R1 R2 Both R1 & R2 equally The primary motivation for 4m SOAR vs 0.6-m MSU is a. b. c. R1 R2 Both R1 & R2 equally 5