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Topic: Arago spot

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	Arago spot
		An Arago spot is a bright point which, owing to diffraction, appears at the center of the shadow of a circular object in light from a point source[?].
		Siméon Poisson deduced from Augustin Fresnel's theory the necessity of a bright spot at the centre of the shadow of a circular opaque obstacle.
		With this counterintuitive result Poisson hoped to disprove the wave theory; however Dominique Arago experimentally verifed the prediction and today the demonstration goes by the name "Poisson's (Arago's) spot".
	www.ebroadcast.com.au /lookup/encyclopedia/po/Poisson_spot.html (104 words)

	François Arago - Wikipedia, the free encyclopedia
		Arago had succeeded in preserving the records of his survey; and his first act on his return home was to deposit them in the Bureau des Longitudes at Paris.
		Arago's earliest physical researches were on the pressure of steam at different temperatures, and the velocity of sound, 1818 to 1822.
		Arago is also fairly entitled to be regarded as having proved the long-suspected connexion between the aurora borealis and the variations of the magnetic pa ments[?].
	en.wikipedia.org /wiki/Fran%C3%A7ois_Arago (2220 words)

	Arago spot - Wikipedia, the free encyclopedia
		In optics, an Arago spot is a bright point which appears at the center of the shadow of a circular object in light from a point source.
		In 1818 Siméon Poisson deduced from Augustin Fresnel's theory the necessity of a bright spot at the centre of the shadow of a circular opaque obstacle.
		The New Worlds Imager, a proposal to directly image extrasolar planets, relies on Arago's spot to isolate the reflected light of a planet from the sun it orbits.
	en.wikipedia.org /wiki/Arago_spot (300 words)

	FAAC - Ford Amateur Astronomy Club
		Arago spot (D.F.J. Arago) A bright spot that appears in the shadow of a uniform disc being backlit by monochromatic light emanating from a point source.
		Archimedes' principle A body that is submerged in a fluid is buoyed up by a force equal in magnitude to the weight of the fluid that is displaced, and directed upward along a line through the center of gravity of the displaced fluid.
		Poisson originally predicted the existence of such a spot, and used the prediction to demonstrate how the wave theory of light must be in error to produce such a counterintuitive result.
	www.boonhill.net /faac/other/laws.html (8656 words)

	Poisson/Arago Bright Spot Story (Site not responding. Last check: 2007-10-10)
		Using Fresnel's theory, Poisson deduced the seemingly absurd prediction that a bright spot should appear behind a circular obstruction, a prediction he felt was the last nail in the coffin for Fresnel's theory.
		However, Dominique Arago, another member of the judging committee, almost immediately verified the spot experimentally.
		Fresnel won the competition, and, although it may be more appropriate to call it "the Spot of Arago," the spot goes down in history with the name "Poisson's bright spot" like a curse.
	www.physics.ucla.edu /~dauger/fresnel/PoissonAragoStory.html (175 words)

	Arago point
		One of the three commonly detectable points, called neutral points, along the vertical circle through the Sun at which the degree of polarization of diffuse sky radiation goes to zero.
		The Arago point (also known as the Arago spot) typically lies about 20° above the antisolar point (where an imaginary ray connecting the Sun and the observer meets the sky), but is found at higher altitudes in turbid air.
		In optics, a bright spot that appears in the center of the shadow of a circular disk illuminated by a point source, caused by diffraction.
	www.daviddarling.info /encyclopedia/A/Arago_point.html (213 words)

	Neptune - Crystalinks
		In France, Arago suggested that the new planet be called Leverrier, a suggestion which was met with stiff resistance outside France.
		Although it looked nearly the same as Jupiter's spot, it was not thought to be a storm but instead an atmospheric hole similar to the hole in Earth's ozone layer.
		It is currently not known why the Great Dark Spot appeared in the first place; whether it is a common occurrence on Neptune or a bizarre phenomenon remains to be seen.
	www.crystalinks.com /neptune.html (3201 words)

	AICS Research, Inc., University Park, NM 88003
		The brightened spot at the center of a shadow caused by light diffracted around an occulter, as predicted first by Poisson in his attempt to reject Fresnel's equations of diffraction.
		Arago set up an experimental apparatus and quickly demonstrated the presence of what has now come to be called "Poisson's Spot."
		Cash solves the Poisson Spot problem by placing petals of highly constrained shapes around the edge of his occulter.
	aics-research.com /lotw/lotw20060612.html (1069 words)

	Honolulu Academy of Art: Traditions of Hawaii: Original Drawings by Jacques Arago
		Captain Freycinet's journals reveal that Arago was an ideal shipmate: "No one onboard proved to be neither more patient, more bold, nor more intelligent, either, to face storms, or to endure the cruelest deprivations." Arago also seemed to have been well received by the Hawaiians he encountered.
		Arago depicted ordinary scenes and activities as well-- the beating of tapa and the process of tattooing.
		Arago, in several of his illustrations, depicted individuals tattooed with rows of small goats running vertically up the leg.
	www.honoluluacademy.org /cmshaa/academy/index.aspx?id=1524 (1022 words)

	Card Model of the Cape Arago Light House, Coos Bay, Oregon
		The third Cape Arago Lighthouse with its 44-foot tower was built of rein' forced concrete in 1934.
		The light and fog signal prevented considerable ship wreck in the vicinity of Cape Arago and many daring sea rescues were undertaken from the old lifesaving station located on the lee side of Lighthouse Island in the early days before and after the turn of the century.
		Although the lighthouse is not open to the public, good views are possible from the hiking trail between the two state parks and from a turnout about a half to three quarter mile south of Sunset Bay.
	www.fiddlersgreen.net /buildings/lighthouses/arago/info/info.htm (647 words)

	The discovery of polarization (polarization.com)
		Arago discovered "interference colors" by placing a sheet of mica between a glass reflector and a calcite prism.
		Arago took revenge on Biot by helping his protege, Fresnel, develop the wave theory of light, as Biot was a lifetime corpuscular.
		Arago performed the experiment and did find the "impossible" bright spot, now known as the "Poisson spot".
	www.polarization.com /history/history.html (2013 words)

	Cook-Austral volcanic chain
		The active Macdonald and recently active Arago Seamounts are represented by fl stars.
		The Arago track appears to be the most homogeneous and could be related to the young Rurutu volcanic episode (1 Ma).
		Arago Seamount is the most recent surface expression of the hotspot responsible for the recent volcanic activity at Rurutu and probably for other volcanoes in the Cook Islands chain.
	www.mantleplumes.org /Cook-Austral.html (1314 words)

	M2-03.HTML (Site not responding. Last check: 2007-10-10)
		The diffraction pattern with its central bright spot is viewed on a distant screen.
		In the photograph at the right the Poisson bright spot is seen on a ground glass screen about twenty feet from the laser, looking back toward the laser beam.
		Siméon Poisson, a member of the judging committee for the competition, was very critical of the wave theory of light.
	www.physics.umd.edu /lecdem/services/demos/demosm2/m2-03.htm (335 words)

	Eureka! Stories: Poisson's Spot
		This means that in the middle of the shadow, there would be a faint bright spot.
		He did the experiment as Poisson had described and discovered - to everybody's surprise - that there was indeed a bright spot in the middle of the shadow!
		So instead of proving that Fresnel was wrong, Poisson had done something very important for proving that Fresnel was right - he had used Fresnel's theory to make a prediction that was so wild sounding that if it was true it almost certainly meant that Fresnel's theory was right.
	www.dctech.com /eureka/short-stories/poisson.php (465 words)

	CosmicQuest @ The Children's Museum of Indianapolis (Site not responding. Last check: 2007-10-10)
		At the time of the Voyager encounter, Neptune's most prominent feature was the Great Dark Spot in the southern hemisphere.
		Voyager 2 also saw a smaller dark spot in the southern hemisphere and a small irregular white cloud that zips around Neptune every 16 hours or so now known as "The Scooter" (right).
		It may be a plume rising from lower in the atmosphere, but its true nature remains a mystery.
	www.childrensmuseum.org /cosmicquest/fieldguide/neptune.html (732 words)

	The Infantry (Site not responding. Last check: 2007-10-10)
		As you will recall, Etienne's father, Beaumont Arago, abandoned his family at a tender age, denouncing the name of his father, one Francois Arago.
		This of course further alienated himself from the once famed prestige of his grandfather, Francois Arago.
		Arago, Le Vicomte de Auxerre, however was the legitimate offspring of the famed Francois Arago, and was bestowed with all honours that should have befallen his father, after the elder died of diabetic complications in a hospice in Paris in 1853.
	theinfantry.blogspot.com (7315 words)

	Poisson's spot (Site not responding. Last check: 2007-10-10)
		In this modern version of the experiment a laser beam is first diffracted through a pinhole that acts as a spacial filter.
		The diffraction pattern with its central bright spot is viewed on a distant screen at the end of the optical rail.
		Fresnel claimed that if light were a wave there would be a bright spot on the axis of a sphere illuminated by a monochromatic light beam.
	www.physics.brown.edu /physics/demopages/Demo/optics/demo/6c2010.htm (146 words)

	UNPh27
		A piece of paper with a grease spot is moved between two light sources until the spot disappears.
		With a bright spot at the object point of a concave mirror and the eye at the image point the whole mirror seems to have the same surface brightness as the spot.
		The sparkling of a spot illuminated by a laser beam on the wall is caused by random interference patterns caused by scattered light speckle spots and random diffraction.
	www.uq.edu.au /_School_Science_Lessons/UNPh27.html (4156 words)

	Pinhole Visions - Archive 371
		In this region, the smaller the hole, the larger the spot.
		Evidently, the pinhole that gives the smallest spot lies in the region between the geometrical optics region depicted in Fig.
		The spot has to be large enough to cast a shadow, and the distance from the spot to the screen has to be well under s
	www.pinhole.com /archive/371 (5032 words)

	Cape Arago Rubber Stamps - Mounting Your Unmounted Rubber Stamps
		Mounting your own art rubber stamps may seem like a lot of work, but it is much easier than you think.
		The method is as above, though the paper index must only be glued in one spot to hold it while the tape is applied.
		It may extend down over the sides of the mount or only cover the very top, but press firmly getting any air bubbles out for a tight and water proof seal.
	www.capearagorubberstamps.com /mounting_instructions.htm (2425 words)

	Oregon Coast Tidepools
		Because it is covered by water most of the time, the low intertidal zone has the greatest diversity of organisms in the tidal area.
		Even though the reef can be reached at low tide from the tidepools at the North Cove of Cape Arago, the reef is part of the Oregon Islands National Wildlife Refuge and is closed to all public use.
		However, a viewing area along the Cape Arago Highway provides a good vantage point from which to watch marine mammals and birds with binoculars or a spotting scope.
	www.fhsu.edu /biology/Eberle/PacificNW/OregonCoastTidepools.html (902 words)

	TripCheck - Oregon Department of Transportation
		From North Bend, take Cape Arago Highway to Charleston, a working fishing port, and a great point of departure for a charter fishing trip.
		The Park was once the site of a grand estate built by lumber baron, Louis B. Simpson; the five acre gardens of the Simpson estate, filled with exotic plants from around the world, are now open to the public.
		Bandon is a popular getaway spot on the southern coast.
	www.tripcheck.com /Pages/SBcharleston.asp (383 words)

	[No title]
		Simeon Poisson pointed out that if Fresnel's wave theory was correct, the shadow of a disk cast by a point source of light should have a bright spot at its center.
		The coherent light from a point source (or a laser) diffracts around the edge of the disk and the light that arrives at the center interferes constructively to produce a bright spot.
		This very unexpected result was experimentally verified by Francois Arago and this is now known as "Arago's spot".
	www.eiu.edu /~ddavis/chapter_20/ch20_4.htm (1019 words)

	diffraction pattern AKA as "Poisson's (Arago's) spot" (Site not responding. Last check: 2007-10-10)
		I believe the phenomena you are referring is related to Fresnel diffraction and diffraction around a circular obstacle and is called Poisson's or Arago spot.
		necessity of a bright spot at the center of the shadow of a circular opaque obstacle.
		verified the prediction and today the demonstration goes by the name "Poisson's (Arago's) spot".
	www.sasked.gov.sk.ca /forum/science/archive/messages/1303.html (165 words)

	Optics
		A glass slide containing a variety of single slits of different widths (as well as double slit and grating configurations) can be placed in front of a laser, and the diffraction pattern viewed on the screen.
		A small circular object is placed in front of a laser beam, and the diffraction pattern, with a bright spot in the very center of the shadow, is observed on the screen.
		Note: this is hard to see in a large class unless students are allowed to come closer to the screen.
	www.columbia.edu /cu/physics/rce/main/demo/optics.html (666 words)

	Oregon Surf Spots - South Coast
		Bastendorff beach is a wide, sandy cove defined by Yoakam Head and the south jetty at the entrance to Coos Bay.
		Protected from prevailing NW summer winds by the jetty, this spot can be a rare summertime haven.
		Good beginner spot, except at low tide when it can dredge pretty heavily.
	www.oregonsurf.com /html/surfspots_south.html (223 words)

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