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Transcript
Telescopes and Spacecraft Astronomy 311 Professor Lee Carkner Lecture 7 How Do We Learn About The Solar System? View from Earth: View remotely: Other methods: visit in person (Moon only) find pieces of solar system that have visited us (meteorite) How Do Telescopes Work? Telescopes: Focus light to produce an image Light gathering ability (not magnification) is the most important attribute of a telescope Lenses 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 If you put a second lens (eyepiece) behind the first lens(objective), you can magnify the image Magnification is equal to the ratio of the focal lengths in practice the magnification you can achieve is limited by the blurring effects of the Earth’s atmosphere Refracting Telescope Giant Refractor at Yerkes Observatory Refractors and Reflectors It is hard to make large refracting telescopes A curved mirror can be used to gather and focus the light instead (reflecting telescope) 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 The Hobby-Eberly Telescope Types of Detectors Eye -- Photographic plate -Charge Coupled Device (CCD) -- more sensitive and easier to use than a plate, allows you to store and reduce data electronically Today, light is moved around with fiber optic cables and data is moved electronically The Electromagnetic Spectrum Every photon (light particle) has a wavelength which places it in the electromagnetic spectrum The wavelength relates to energy We see different wavelengths of visible light as colors We want to view all types of electromagnetic radiation The Electromagnetic Spectrum Telescope Taxonomy Radio and Millimeter -- penetrates atmosphere and everything else Example: The VLA (Very Large Array) Infrared (IR) -- we feel as heat Example: IRAS (Infrared Astronomical Satellite) Optical -- what our eyes can see Example -- Hubble Space Telescope More Telescope Taxonomy Ultraviolet (UV) -- high energy radiation, causes sunburn Example -- IUE (International Ultraviolet Explorer) X-ray -- very high energy Example -- Chandra X-ray Observatory Gamma Ray -- the highest energy Example -- Compton Gamma Ray Observatory The VLA Hubble Space Telescope Spacecraft Since the 1960’s we have sent probes to study the planets close up Types of spaces probes: Fly-by -Example: Voyagers I and II Orbiter -Example: Mars Global Surveyor Lander -Example: Mars Pathfinder Getting to The Planets Spacecraft don’t zoom around the Solar System like in science fiction Use small thrusters to maneuver (remember Newton’s First Law -- Inertia) Least Energy Orbit After that it follows 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 Time to get to Mars Sun Earth Spacecraft Orbit P2=a3 aEarth = 1 AU Time = = Least Energy Orbit to Mars 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) Next Time Read 15.1-15.4, 6.7 Quiz #1 on Monday Study hard!