Amateur Astronomy & Telescopes Josh Webster 2/5/2014 Amateur Astronomy & Telescopes - Webster 1
Outline What is amateur astronomy? Misconceptions in visual astronomy - Rods & Cones - Magnification!!! Common telescope types - Advantages/disadvantages Eyepieces Basic related equations Tallahassee Astronomical Society (TAS) 2/5/2014 Amateur Astronomy & Telescopes - Webster 2
What is amateur astronomy? It s casually observing the sky. It is considered a hobby. Many professional astronomers also enjoy amateur astronomy. Amateur astronomers can contribute to science. Two main branches: visual and photographic http://www.celestronimages.com/details.php?image_id=7230 Notable amateur astronomers: Thomas Bopp & Alan Hale (PhD) comet Hale-Bopp George Alcock several comets & novae David H. Levy comet Shoemaker-Levy 9 and 22 others Grote Reber pioneer of radio astronomy; first sky survey in radio freq.; worlds only radio astronomer for almost an entire decade. 2/5/2014 Amateur Astronomy & Telescopes - Webster 3
Common/Beginner Misconceptions in Amateur Astronomy Disadvantages of the Human Eye Magnification!!! http://www.abrutis.com/photo-probleme+de+telescope-29456.html 2/5/2014 Amateur Astronomy & Telescopes - Webster 4
Disadvantages of the Human Eye Two types of photoreceptors: rods and cones. Visual astronomy primarily deals with rods. Rods: Take over in low light More numerous than cones Much higher sensitivity Little response to red light Downfalls: - No color detection - Slow response - Best in peripherals - Low acuity Rods & Cones http://www.anatomybox.com/retina-sem/retina-rods-and-cones-sem/ 2/5/2014 Amateur Astronomy & Telescopes - Webster 5
Disadvantages of the Human Eye Similar to Human Eye Hubble Space Telescope http://en.wikipedia.org/wiki/file:orion-nebula_a_a_common.jpg DSLR Camera http://en.wikipedia.org/wiki/file:the_orion_nebula_m42.jpg http://en.wikipedia.org/wiki/file:orion_nebula_-_hubble_2006_mosaic_18000.jpg Albeit Hubble is in space. 2/5/2014 Amateur Astronomy & Telescopes - Webster 6
Not Magnification, AMPLIFICATION! Magnification is by far the most common misconception and usually the least important factor. A manufacturer marketing strategy Average max resolvable magnification (on Earth with virtually no atmospheric turbulence) 100x The more you magnify the sky, the more you magnify the atmosphere. High magnification is usually only useful for splitting double/binary stars. Aperture: - The diameter of the primary mirror. Usually given in mm or in. - Almost always the most important factor of a telescope. - Amplifies the light signal. Commonly referred to as Light Gathering Power (LGP). - Allows us to see dimmer objects. 2/5/2014 Amateur Astronomy & Telescopes - Webster 7
Common Telescope Types Reflector (Newtonian) Schmidt-Cassegrain http://en.wikipedia.org/wiki/file:newton-teleskop.svg http://en.wikipedia.org/wiki/file:schmidt-cassegrain-telescope.svg Refractor (Keplerian) Maksutov-Cassegrain http://en.wikipedia.org/wiki/file:cassegrain-telescope.svg http://en.wikipedia.org/wiki/file:maksutov_spot_cassegrain.png 2/5/2014 Amateur Astronomy & Telescopes - Webster 8
Telescope Types Continued Newtonian Reflector Schmidt-Cassegrain http://images1.opticsplanet.com/365-240-ffffff/opplanetcelestron-nexstar-130-telescope.jpg Refractor http://3.bp.blogspot.com/-qwbub7lvqye/tw4ob_dzuoi/ AAAAAAAAA6Q/qyH90ARmHbs/s400/11063_cge1400_mid.gif Maksutov-Cassegrain http://www.novac.com/resources/reviews/images/80ed1.jpg http://img3.findthebest.com/sites/default/files/810/media/images/or ion_apex_127mm_maksutov-cassegrainz_telescope_75704.jpg 2/5/2014 Amateur Astronomy & Telescopes - Webster 9
Advantages/Disadvantages of Telescope Types Type Advantages Disadvantages Cost Comparison Refractor Simple design, little maintenance, no secondary mirror obstruction, great optics for Astrophotography (AP) Highest cost for size, heavy, aperture limitations, not great for DSO s Orion ED80 (80 mm 3.14 ) w/o mount - $500 LGP = 130x Reflector Least expensive design, great for DSO s due to no size limitations Some light loss from secondary mirror, more maintenance due to exposed optics Orion XT10 (254 mm 10 ) - $600 LGP = 1317x Catadioptric Combines advantages of the other types, little maintenance, great for AP More expensive than reflectors, some light loss from secondary mirror Celestron 127 Mak (127mm 5 ) - $500 LGP = 329x The focal ratio of a telescope also plays an important role. It is a measure of the speed of a telescopes optics. (Equation later) 2/5/2014 Amateur Astronomy & Telescopes - Webster 10
Eyepieces (EPs) http://www.vikdhillon.staff.shef.ac.uk/teaching/phy 217/telescopes/eyepieces.jpg http://www.optcorp.com/pdf/opt/edu/eyepiece-580x393.gif Many designs; ranging from single to eight element designs. A good eyepiece in one telescope may not give the same views in another. (e.g. focal ratio) A good eyepiece for viewing planets may not work as well for viewing Deep-sky Objects (DSOs). Eye-relief may be important to you. 2/5/2014 Amateur Astronomy & Telescopes - Webster 11
Basic Related Equations Exit Pupil = focal length EP focal ratio scope Diameter of image projected out of the eyepiece. Focal Ratio = focal length scope Aperture Magnification = focal length scope focal length EP Max Useful Magnification = 60 Aperture Minimum Useful Magnification = 3 Aperture Limiting Magnitude = 2 + 5log Aperture Light Gathering Power = Resolution arcseconds = Resolution arcseconds = Aperture (mm) 7 mm 138 Aperture (mm) 116 Aperture(mm) A measure of a telescopes speed. Also called f/stop or f-ratio. The magnification of a telescope using a specific focal length eyepiece. A measure of how far you can push the limits of your telescope. A more realistic approximation is to use 30 instead of 60. A good way to see if you can split certain binary stars. Minimum magnification is good for viewing large areas of the sky. Tells you the highest magnitude object that can be resolved for a given telescope aperture. A measure of the ability of a telescope to gather light. 7mm is the average diameter of the dark-adapted pupil. The Rayleigh limit. A general measure of the ability of a telescope to distinctly resolve two stars of equal magnitude. The Dawes limit. Reached when the airy disk of one star is in the diffraction ring of another, and the stars are seen as just barely touching. 2/5/2014 Amateur Astronomy & Telescopes - Webster 12
Conclusion Amateur astronomy can be casual or serious and scientific. There are physical phenomena associated with the human eye that effect what you see. Size matters! Amplification >> Magnification Large reflectors are cheaper to build than comparables. A good eyepiece even on a cheap telescope can make a world of difference, and so can a cheap eyepiece on a good telescope. Most important equations: focal ratio, and magnification. 2/5/2014 Amateur Astronomy & Telescopes - Webster 13
Tallahassee Astronomical Society (TAS) Meetings: 3 rd Saturday of the month Challenger Center (IMAX). Planetarium show: the 1 st Saturday of every month at the Challenger, Free! Observatory! Mag lab open house Feb. 22 nd. If anyone is interested in coming out on an observing session let me know! 2/5/2014 Amateur Astronomy & Telescopes - Webster 14
References Nave, R. (2000). Rods and Cones. Retrieved January 24, 2014, from Hyperphysics: http://hyperphysics.phyastr.gsu.edu/hbase/vision/rodcone.html Sharma, G. (n.d.). Understanding Telescopes. Retrieved January 24, 2014, from Telescopes.com: http://www.telescopes.com/telescopes/helpunderstandingtelescopesarticle.c fm Wikipedia. (2014, January 17). Amateur Astronomy. Retrieved January 24, 2014, from Wikipedia: http://en.wikipedia.org/wiki/amateur_astronomy Culp, R. (2012, November 16). Telescope Equations. Retrieved January 24, 2014, from RocketMime: http://www.rocketmime.com/astronomy/telescope/telescope_eqn.html 2/5/2014 Amateur Astronomy & Telescopes - Webster 15
Questions? 2/5/2014 Amateur Astronomy & Telescopes - Webster 16