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Amateur Astronomy & Telescopes
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Josh Webster
Outline
โข What is amateur astronomy? โข Misconceptions in visual astronomy - Rods & Cones - Magnification!!! โข Common telescope types - Advantages/disadvantages โข Eyepieces โข Basic related equations โข Tallahassee Astronomical Society (TAS)
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What is amateur astronomy?
Notable amateur astronomers: Thomas Bopp & Alan Hale (PhD) โ comet Hale-Bopp George Alcock โ several comets & novae David H. Levy โ comet Shoemaker-Levy 9 and 22 others Grote Reber โ pioneer of radio astronomy; first sky survey in radio freq.; worlds only radio astronomer for almost an entire decade.
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โข Itโs casually observing the sky. โข It is considered a hobby. โข Many professional astronomers also enjoy
amateur astronomy. โข Amateur astronomers can contribute to
science. โข Two main branches: visual and photographic
http://www.celestronimages.com/details.php?image_id=7230
Common/Beginner Misconceptions in Amateur Astronomy
โข Disadvantages of the Human Eye
โข Magnification!!!
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http://www.abrutis.com/photo-probleme+de+telescope-29456.html
Disadvantages of the Human Eye Rods & Cones
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http://www.anatomybox.com/retina-sem/retina-rods-and-cones-sem/
โข Two types of photo-receptors: โrodsโ and โconesโ.
โข Visual astronomy primarily deals with rods.
Rods: โข Take over in low light โข More numerous than cones โข Much higher sensitivity โข Little response to red light โข Downfalls: - No color detection - Slow response - Best in peripherals - Low acuity
Disadvantages of the Human Eye
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Similar to Human Eye
http://en.wikipedia.org/wiki/File:Orion-Nebula_A_A_Common.jpg
DSLR Camera
Hubble Space Telescope
http://en.wikipedia.org/wiki/File:Orion_Nebula_-_Hubble_2006_mosaic_18000.jpg http://en.wikipedia.org/wiki/File:The_Orion_Nebula_M42.jpg Albeit Hubble is in space.
Not Magnification, AMPLIFICATION!
โข Magnification is by far the most common misconception and usually the least important factor.
โข A manufacturer marketing strategy โข Average max resolvable magnification (on Earth with virtually no
atmospheric turbulence) โ 100x โข The more you magnify the sky, the more you magnify the atmosphere. โข 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 โsignalโ. Commonly referred to as Light Gathering
Power (LGP). - Allows us to see dimmer objects.
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Common Telescope Types
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http://en.wikipedia.org/wiki/File:Newton-Teleskop.svg
http://en.wikipedia.org/wiki/File:Cassegrain-Telescope.svg
http://en.wikipedia.org/wiki/File:Maksutov_spot_cassegrain.png
Maksutov-Cassegrain
Schmidt-Cassegrain
Refractor (Keplerian)
Reflector (Newtonian)
http://en.wikipedia.org/wiki/File:Schmidt-Cassegrain-Telescope.svg
Telescope Types Continuedโฆ
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Newtonian Reflector
Refractor
Schmidt-Cassegrain
Maksutov-Cassegrain
http://img3.findthebest.com/sites/default/files/810/media/images/Orion_Apex_127mm_Maksutov-CassegrainZ_Telescope_75704.JPG
http://images1.opticsplanet.com/365-240-ffffff/opplanet-celestron-nexstar-130-telescope.jpg http://3.bp.blogspot.com/-QWbUB7lvqYE/TW4oB_dzUOI/
AAAAAAAAA6Q/qyH90ARmHbs/s400/11063_cge1400_mid.gif
http://www.novac.com/resources/reviews/images/80ed1.jpg
Advantages/Disadvantages of Telescope Types
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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 DSOโs
Orion ED80 (80 mm โ 3.14โ) w/o mount - $500 LGP = 130x
Reflector Least expensive design, great for DSOโs due to no size limitations
Some light loss from secondary mirror, more maintenance due to exposed optics
Orion XT10 (254 mm โ 10โ) - $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 โ 5โ) - $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)
Eyepieces (EPs)
โข Many designs; ranging from single to eight element designs. โข Focal length - 17mm โ 40 mm for DSOโs - 6 โ 17 mm for Stars, Planets and some Clusters โข Eye-relief may be important to you.
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http://www.optcorp.com/pdf/OPT/EDU/eyepiece-580x393.gif
http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/eyepieces.jpg
Basic Related Equations
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๐ธ๐ฅ๐๐ก ๐๐ข๐๐๐ =๐๐๐๐๐ ๐๐๐๐๐กโ๐ธ๐
๐๐๐๐๐ ๐๐๐ก๐๐๐ ๐๐๐๐
Diameter of image projected out of the eyepiece.
๐ญ๐๐๐๐ ๐น๐๐๐๐ =๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐๐
๐จ๐๐๐๐๐๐๐
A measure of a telescopes speed. Also called f/stop or f-ratio.
๐ด๐๐๐๐๐๐๐๐๐๐๐๐ =๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐๐๐
๐๐๐๐๐ ๐๐๐๐๐๐๐ฌ๐ท
The magnification of a telescope using a specific focal length eyepiece.
๐๐๐ฅ ๐๐ ๐๐๐ข๐ ๐๐๐๐๐๐๐๐๐๐ก๐๐๐ = 60 ร ๐ด๐๐๐๐ก๐ข๐๐
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.
๐๐๐๐๐๐ข๐ ๐๐ ๐๐๐ข๐ ๐๐๐๐๐๐๐๐๐๐ก๐๐๐ = 3 ร ๐ด๐๐๐๐ก๐ข๐๐ Minimum magnification is good for viewing large areas of the sky.
๐ณ๐๐๐๐๐๐๐ ๐ด๐๐๐๐๐๐๐ ๐ = ๐ + ๐๐ฅ๐จ๐ ๐จ๐๐๐๐๐๐๐
Tells you the highest magnitude object that can be resolved for a given telescope aperture.
๐ณ๐๐๐๐ ๐ฎ๐๐๐๐๐๐๐๐ ๐ท๐๐๐๐ =๐จ๐๐๐๐๐๐๐ (๐๐)
๐ ๐๐
๐
A measure of the ability of a telescope to gather light. 7mm is the average diameter of the dark-adapted pupil.
๐ ๐๐ ๐๐๐ข๐ก๐๐๐ ๐๐๐๐ ๐๐๐๐๐๐ =138
๐ด๐๐๐๐ก๐ข๐๐ (๐๐)
The Rayleigh limit. A general measure of the ability of a telescope to distinctly resolve two stars of equal magnitude.
๐ ๐๐ ๐๐๐ข๐ก๐๐๐ ๐๐๐๐ ๐๐๐๐๐๐ =116
๐ด๐๐๐๐ก๐ข๐๐(๐๐)
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.
Conclusion
โข Amateur astronomy can be casual or serious and scientific. โข There are physical phenomena associated with the human
eye that effect what you see. โข Size matters! Amplification >> Magnification โข Large reflectors are cheaper to build than comparables. โข A good eyepiece even on a cheap telescope can make a
world of difference, and so can a cheap eyepiece on a good telescope.
โข Most important equations: focal ratio, and magnification.
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Tallahassee Astronomical Society (TAS)
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If anyone is interested in coming out on an observing session let me know!
โข Meetings: 3rd Saturday of the month Challenger Center (IMAX).
โข Planetarium show: the 1st Saturday of every month at the Challenger, Free!
โข Observatory! โข Mag lab open house Feb. 22nd.
References
Nave, R. (2000). Rods and Cones. Retrieved January 24, 2014, from Hyperphysics: http://hyperphysics.phy-astr.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.cfm 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?
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