02 Light And Telescopes Mc Neely 2008

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<ul><li> 1. Astronomy Light &amp; Telescopes Edwin Hubble and the 48-inch Palomar Telescope in 1949</li></ul> <p> 2. Light </p> <ul><li>A form of wave motion </li></ul> <ul><li>Waves: </li></ul> <ul><li><ul><li>Rise and fall </li></ul></li></ul> <ul><li><ul><li>Transfer energy, but not material </li></ul></li></ul> <ul><li><ul><li>Features : Crest, trough, wavelength, frequency </li></ul></li></ul> <ul><li>Photon : Light can also behave as a particle named a photon </li></ul> <ul><li>Frequency : The number of waves that pass a fixed point in a given time </li></ul> <p> 3. Waves 4. Visible Light </p> <ul><li>Human eye responds to visible light which is just one portion of the electromagnetic spectrum </li></ul> <ul><li>Visible Light = 4000-7000 Angstroms </li></ul> <ul><li>Visible Spectrum: ROYGBIV </li></ul> <p> 5. Wavelength Relationship 6. EM Spectrum Short wavelengths Long wavelengths 7. Speed of Light </p> <ul><li>The speed of light is represented as c in Einsteins famous equation (E=mc 2 ) </li></ul> <ul><li> c = 186,000 miles per second (300,000 km per second) </li></ul> <ul><li> Speed limit of the universe, nothing can travel faster </li></ul> <p> 8. Light Years </p> <ul><li>Light Year : Distance measure of light travel in one year, about 6 trillion miles </li></ul> <ul><li>Light year is a measure of distance </li></ul> <ul><li>Light from sun = 8 light minutes </li></ul> <p> 9. Light Travel Time </p> <ul><li>Light from nearest star = 4.3 light years </li></ul> <ul><li>Diameter of Milky Way Galaxy = 100,000 ly </li></ul> <ul><li>Distance to Andromeda Galaxy = 2.3 million ly </li></ul> <ul><li>Distance to Virgo Galaxy Cluster = 50 million ly </li></ul> <p> 10. Time Travel </p> <ul><li>Light takes time to travel through space </li></ul> <ul><li>The farther away we look in distance, the further back we look in time </li></ul> <ul><li>Ex: The star Sirius lies 8 light years away. </li></ul> <ul><li>When we look at Sirius, we are seeing the star as it was 8 years ago </li></ul> <p> 11. Types of Telescopes </p> <ul><li>Three types :</li></ul> <ul><li>Refractors </li></ul> <ul><li><ul><li>Use lenses to collect light </li></ul></li></ul> <ul><li>Reflectors </li></ul> <ul><li><ul><li>Use mirrors to collect light </li></ul></li></ul> <ul><li>Compound </li></ul> <ul><li><ul><li>Both lenses and mirrors </li></ul></li></ul> <p> 12. Telescope Designs http://www.aw-wrdsmth.com/scuttlebutt/telescope-daigram.jpg 13. Refractors Department store refractor Modern APO refractor 14. Types of Reflectors </p> <ul><li>The Newtonian reflector was first designed by Isaac Newton and uses two mirrors to collect light </li></ul> <ul><li>In recent years, Newtonians have been popular in the Dobsonian design where the telescope tube is mounted like a cannon </li></ul> <p>Newtons original telescope http://telescopemaking.org/images/newtontele.jpg 15. Newtonian &amp; Dobsonian Meade Dobsonian telescope http://www.nachohat.org/images/static/meade_starfinder.jpg Eyepiece Newtonian optical diagram John Dobson 16. 6-in Newtonian on a Dobsonian Mount 6-in indicates that the telescope uses a 6-inch diameter mirror as its main light gathering optic This Orion Telescopes XT6 is an excellent scope for beginners and is reasonably priced 17. Compound Scopes: Schmidt-Cassegrain Cutaway view of an SCT Maksutovs are similar yet use a more curved front lens Main mirror Lens Meade Telescopes 8-inch SCT Eyepiece 18. Properties of Telescopes </p> <ul><li>Objective : Main mirror or lens </li></ul> <ul><li>Aperture : Diameter of the objective, determines amount of light gathered by the scope </li></ul> <ul><li>Eyepiece : Set of small magnifying lenses that forms the image viewed through a telescope </li></ul> <ul><li>Focal Length : Distance from the objective to the image in the eyepiece </li></ul> <p> 19. Refractor Objective Lens http://www.rocketroberts.com/astro/refractor.htm 20. Magnification </p> <ul><li>Magnification = </li></ul> <ul><li>Telescope focal lengthEyepiece focal length </li></ul> <ul><li>Ex : 2800mm focal length Schmidt Cassegrain telescope, with 32mm and 25 mm focal length eyepieces: </li></ul> <ul><li>2800mm32mm = 87.5x </li></ul> <ul><li>2800mm16mm = 112x </li></ul> <p> 21. Useful Magnification </p> <ul><li>Highest useful magnification usually equals 50 times the aperture of the scope in inches: </li></ul> <ul><li>Useful magnification = 50 * Aperture (inches) </li></ul> <ul><li>Ex : What is the highest useful magnification of a 2.4-inch department store telescope and a 6-inch reflecting telescope? </li></ul> <ul><li>2.4-in * 50 = 120x </li></ul> <ul><li>6-in * 50 = 300x </li></ul> <p> 22. Telescope Formula </p> <ul><li>A useful relationship for describing telescopes is the following: </li></ul> <ul><li>f/number = </li></ul> <ul><li>Focal lengthAperture</li></ul> <ul><li>Compare : </li></ul> <ul><li><ul><li>8-inch reflecting telescope of 900mm focal length </li></ul></li></ul> <ul><li><ul><li>70 mm refractor of 480 mm focal length </li></ul></li></ul> <p> 23. Telescope Formula Examples 8-inch Reflector 2.7-inch Refractor Aperture (mm) 200mm 70mm Focal Length (mm) 900mm 480mm f/Number 900/200=f/4.5 480/70=f/6.8 Magnification (32mm eyepiece) 900/32=28x 480/32=15x 24. Two Scopes 25. Telescopes and Light Collecting </p> <ul><li>Small increases in aperture can dramatically improve telescopic views </li></ul> <ul><li>This is because area is proportional to thesquareof a telescopes diameter</li></ul> <ul><li>Telescopes promoted as having highmagnificationare meant to deceive consumers becauseapertureis the true way to access a telescopes ability </li></ul> <p> 26. Aperture Demo http://www.clarkvision.com/visastro/m51-apert/index.html The animation compares sketches of the Whirlpool Galaxy (M51) through 6, 8, and 12.5 in telescopes 27. Telescope Aberrations </p> <ul><li>Chromatic : Inability of alensto focus all colors of the spectrum.</li></ul> <ul><li><ul><li>Ex: Color error or chromatic aberration in refracting telescopes </li></ul></li></ul> <ul><li>Spherical : Inability of amirrorto reflect all light to a single point. </li></ul> <ul><li><ul><li>Ex: Poorly made reflecting telescope mirrors.</li></ul></li></ul> <ul><li><ul><li>Original Hubble Space Telescope mirror </li></ul></li></ul> <p> 28. Binoculars </p> <ul><li>Useful for stargazing </li></ul> <ul><li>Two telescope tubes mounted side to side </li></ul> <ul><li>Usually have fixed magnifications </li></ul> <ul><li>Ex: Pair labeled 7x50, means 7x magnification, front objective lenses of 50mm diameter </li></ul> <p>Milky Way starfield 29. Telescope Seeing </p> <ul><li>The term seeing refers to the steadiness of the atmosphere overhead </li></ul> <ul><li>Poor atmospheric seeing produces twinkling (star scintillation) </li></ul> <ul><li>Unsteady air produces poor telescope images without sharp focus </li></ul> <ul><li>Telescopes need to acclimate to outside temperature </li></ul> <p>http://en.wikipedia.org/wiki/Astronomical_seeing Lunar crater Clavius in poor seeing 30. Star Scintillation This montage of photographs shows how a single stars image is distorted over time by atmospheric seeing or turbulence Ideal star image 31. Why do Stars Twinkle? Turbulent air causes a stars image to distort 32. Light Pollution </p> <ul><li>Stargazing is difficult in the city </li></ul> <ul><li>Excess artificial light that enters the night sky is termed light pollution </li></ul> <ul><li>Observatories are built in remote places away from cities if possible </li></ul> <p>http://www.apstas.com/astrotas/glow.jpg 33. Effects of LP http://www.spaceweather.com/swpod2003/20aug03/Carlson1.jpg 34. Kitt Peak LP The view from Kitt Peak National Observatory of the Tuscon, Arizona skyline in 1959 The same skyline in 1972 35. US at Night http://archives.cnn.com/2000/US/08/24/dimming.the.lights.ap/large.usa.lights.jpg 36. Eastern US http://www.seds.org/~aschultz/images/light-pollution/us_nite.gif 37. Europe http://www.clocktower.demon.co.uk/stockgrove/light/europe.jpg </p> <ul><li>Notice how brightness can indicate wealth and development; Poor countries have much less outdoor lighting </li></ul> <p> 38. Earth at Night (Click Below) http://veimages.gsfc.nasa.gov//1438/earth_lights_lrg.jpg 39. Good and Bad Lighting </p> <ul><li>Good light fixtures shine their light only toward the ground, not toward your eyes or the sky </li></ul> <ul><li>A bad light fixture is one in which the uncovered bulb is visible </li></ul> <p> 40. Light Fixtures </p> <ul><li>Billboards that emit light straight into the sky are bad </li></ul> <p> 41. Observatories </p> <ul><li>Observatories provide a permanent installation to house a telescope </li></ul> <ul><li>Modern, professional observatories are usually located on mountain tops to take advantage of better seeing </li></ul> <ul><li>Ex : Keck Observatory on Mauna Kea in Hawaii </li></ul> <ul><li>Amateur astronomers build backyard observatories of many types </li></ul> <p> 42. Keck Observatory http://www.wainscoat.com/astronomy/keck-moonlight.jpg </p> <ul><li>The twin Keck 10-meter telescopes are the largest in the world </li></ul> <ul><li>The telescopes are located on the 14,000 foot elevation summit of Mauna Kea in Hawaii </li></ul> <ul><li>Each telescope uses a mirror composed of 36 hexagonal segments arranged in a mosaic pattern </li></ul> <ul><li>The individual mirrors act together like a single mirror </li></ul> <p> 43. Keck Mirror http://www.astro.ucla.edu/~seth/albums/images/mirror3.jpg 44. Backyard Observatory Roof rolls off for easy access to sky SCT mounted on a permanent pier aka Mini Keck 45. Summary : Telescope Formulas </p> <ul><li>Magnification= </li></ul> <ul><li>Telescope Focal Length (mm)Eyepiece Focal Length (mm) </li></ul> <ul><li> Useful Magnification=</li></ul> <ul><li>50 * Aperture (in) </li></ul> <ul><li>f/Number= </li></ul> <ul><li>Telescope Focal length (mm)Telescope Aperture (mm) </li></ul>