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Transcript
ASTR2050 Spring 2005 Lecture 10am 1 February 2005 Please turn in your homework now! In this class we will cover Telescopes: • What does a telescope do? • Kinds of optical telescopes • Photography and light detection • Observing outside the visible 1 This is a telescope: Hale Telescope (Mt Palomar) See Kutner Figure 4.7a 2 So is this: VLA (Kutner Fig.4.30) 3 These are telescopes, too: Chandra Hubble Space Telescope 4 What does a telescope do? Telescopes perform two main functions: 1. Light gathering: The “aperture” of a telescope is much larger than the pupil of the eye. Detectors allow it to “integrate” over a longer time. 2. Angular resolution: Waves “diffract” when they pass through an opening, and make images “fuzzy”. Diffraction is smaller for large openings. 5 Light gathering power Diameter of the pupil of your eye: 5mm or so Diameter of the “aperture” of a telescope: BIGGER! Relative light gathering power is just the area of the (circular) aperture. Area = !(D/2) 2 Relative LGP = (DTel /DEye) 2 !m = 2.5 log10(LGP) 6 Example 4.1 in Kutner How many magnitudes fainter can the eye observe using a 1m diameter telescope? ! " 2 2 !m = 2.5 log10 (1m) /(5mm) = 11.5 So, if your naked eye can see down to magnitude 6, this telescope lets you see down to magnitude 17.5 7 Angular Resolution First discuss “diffraction”: General phenomenon for waves passing through some opening 8 Example: Water waves Go to “ripple tank” Java applet 9 Similar for “circular aperture” 10 So, back to “angular resolution”... How close together can two objects be and still be “resolved”? 11 The Rayleigh Criterion Images “resolved” when the peaks are separated by the distance between minima for a single image. i.e. “resolution” ! ≈ D 12 Kinds of optical telescopes • Refracting telescopes - Magnification • Reflecting telescopes - Newtonian, Cassegrain, and Coude focal configurations • The Hubble Space Telescope 13 Refracting telescopes See Also Kutner Fig.4.5 fOb j magni f ication = fEye fEye 14 fOb j Yerkes Observatory Refracting Telescope 40 Inch Diameter Objective It is the largest refracting telescope in the world! It is hard to make a large lens that is optically “perfect”, and to keep it that way! 15 Another problem with refracting telescopes: Chromatic aberration It can be corrected to some extent, but not perfectly. 16 Reflecting telescopes Fix problems encountered with refracting telescopes 17 The Keck 10m Telescope The (two) largest telescopes in the world 18 The Hubble Space Telescope Why put a telescope in space? 1. Absence of atmospheric distortion 2. Near UV and IR 3. Unlimited seeing time 19 Atmospheric Distortion Demonstration of “speckling” 20 When the Hubble Telescope got its “eyeseight” corrected Will the HST ever get serviced again?? 21 Photography and light detection Photography remains a useful “true color” technique. Nowadays, CCD’s are used instead of film. 22 Observing outside the visible Fundamental principles of “light” gathering and angular resolution are the same! But, there are some special tricks, for example, the VLA makes use of radio wave interferometry: 23 X-ray and Gamma Ray astronomy Chandra is a spacecraft The Auger project 24