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Transcript
Telescopes and Spacecraft Astronomy 311 Professor Lee Carkner Lecture 7 How Do Telescopes Work? Telescopes: Focus light to produce an image Quality and light gathering ability (not magnification) are the most important attributes of a telescope telescopes make faint things brighter Lenses Need a lens Lenses bend light (refraction) and focus all of the light incident on the front to a point (focus) a certain distance behind the lens (focal length) Lenses and Refraction Refracting Telescope This produces a refracting telescope mag.= f.l. objective / f.l. eyepiece in practice the magnification you can achieve is limited by the blurring effects of the Earth’s atmosphere Refracting Telescope Refractors and Reflectors Makes them hard to make flawless heavy and hard to support large mirrors are easier to make and support Reflecting Telescopes Problem: The focal point is between the mirror and the sky Cassegrain Telescope -- secondary reflects light through a hole in the primary, most common type of large telescope Cassegrain Reflecting Telescope Telescope Misconceptions Magnification is the most important property of a telescope image quality and light gathering ability (size) are what is important Astronomers peer through an eyepiece Telescopes stick out of the dome Telescopes fold up like a giant pirate’s spyglass Least Energy Orbit Once in space they coast to the planets, following Kepler’s Laws An orbit that intersects the Earth’s orbit at one point and the other planet’s orbit at another point (on the opposite side of the Sun) Mars Sun Earth Spacecraft Orbit Least Energy Orbit to Mars The Electromagnetic Spectrum Every photon (light particle) has a wavelength which places it in the electromagnetic spectrum long wavelength -- low energy short wavelength -- high energy red -- long wavelength blue -- short wavelength So we can explore all physical processes The Electromagnetic Spectrum Telescope Taxonomy Radio and Millimeter penetrates atmosphere and everything else Infrared (IR) some penetrates atmosphere, but to observe all IR wavelengths need to go into space Optical it helps to get above atmosphere (no blurring = sharper images) More Telescope Taxonomy Ultraviolet (UV) some penetrates atmosphere, but to observe all UV wavelengths need to go into space X-ray all X-rays blocked by atmosphere Gamma Ray all Gamma rays blocked by atmosphere Next Time Read 15.1-15.4 , 6.7 Quiz #1 on Monday Study hard! Summary Refracting Telescopes use a lens to bend light to a focus Reflecting Telescopes use a mirror to reflect light to a focus Most large research telescopes are reflectors Astronomers today record and analyze data digitally Summary To observe the entire electromagnetic spectrum you need many different types of telescopes, some of them in space Spacecraft have allowed close up study of the planets Spacecraft reach their destinations by using the gravity of the Sun (or sometimes planets)
