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Black Drop Effect
The black drop effect is an optical phenomenon visible during a transit of Venus and, to a lesser extent, a transit of Mercury. Description Just after astronomical transit#Contacts, second contact, and again just before astronomical transit#Contacts, third contact during the transit, a small black "teardrop" appears to connect Venus's disc to the wikt:limb#Etymology 2, limb of the Sun, making it impossible to time the exact moment of second or third contact accurately. This led to the failure of the attempts during the 18th century transits of Venus to establish a truly precise value for the astronomical unit. The black drop effect was long thought to be due to Venus's thick atmosphere, and indeed it was held to be the first real evidence that Venus had an atmosphere. However, it is now thought by many to be an optical effect caused by the combination of the extreme darkening of the Sun's disk near its apparent edge and the intrinsic imperfection of the viewing apparatus. Ob ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limb Darkening
Limb darkening is an optical effect seen in stars (including the Sun), where the central part of the disk appears brighter than the edge, or ''limb''. Its understanding offered early solar astronomers an opportunity to construct models with such gradients. This encouraged the development of the theory of radiative transfer. Basic theory Optical depth, a measure of the opacity of an object or part of an object, combines with effective temperature gradients inside the star to produce limb darkening. The light seen is approximately the integral of all emission along the line of sight modulated by the optical depth to the viewer (i.e. 1/e times the emission at 1 optical depth, 1/e2 times the emission at 2 optical depths, etc.). Near the center of the star, optical depth is effectively infinite, causing approximately constant brightness. However, the effective optical depth decreases with increasing radius due to lower gas density and a shorter line of sight distance through the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shadow Blister Effect
The shadow blister effect is a visual phenomenon in which a shadow bulges (or blisters) as it approaches another. The effect takes place when two objects are at varying distances between a non-point light source and a background upon which their shadows are cast. As the objects move transversely such that their shadows approach each other, the one nearest the light source begins blocking light from reaching the inside of the other object's penumbra, thereby expanding its umbra. This expansion of the further object's umbra continues until the umbras of both objects meet. This effect can be demonstrated and understood using ray theory. The shadow blister effect is commonly misconceived to be an illusion caused by the combining of the two object's penumbras, aided by factors such as diffraction, nonlinear response, and the eye's inability to differentiate between varying contrasts. See Also *Black drop effect The black drop effect is an optical phenomenon visible during a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charles Green (astronomer)
Charles Green (baptised 26 December 1734 – 29 January 1771) was a British astronomer, noted for his assignment by the Royal Society in 1768 to the expedition sent to the Pacific Ocean in order to observe the transit of Venus aboard James Cook's '' Endeavour''. Early life and education Born sometime in December 1734, Green was the youngest son of Joshua Green, a prosperous farmer who lived near Swinton in Yorkshire. His education, according to his future brother-in-law William Wales, was chiefly at a school near Denmark Street in Soho, London. This school was run by his eldest brother, the clergyman Rev. John Green, and the younger Green went on to become an assistant teacher there, continuing his studies in astronomy until he joined the staff of the Royal Greenwich Observatory in 1760. Career in astronomy Green was appointed as Assistant to the Astronomer Royal, James Bradley, succeeding the astronomer Charles Mason who left to join the expedition to the Cape of Good H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James Cook
James Cook (7 November 1728 Old Style date: 27 October – 14 February 1779) was a British explorer, navigator, cartographer, and captain in the British Royal Navy, famous for his three voyages between 1768 and 1779 in the Pacific Ocean and to New Zealand and Australia in particular. He made detailed maps of Newfoundland prior to making three voyages to the Pacific, during which he achieved the first recorded European contact with the eastern coastline of Australia and the Hawaiian Islands, and the first recorded circumnavigation of New Zealand. Cook joined the British merchant navy as a teenager and joined the Royal Navy in 1755. He saw action in the Seven Years' War and subsequently surveyed and mapped much of the entrance to the St. Lawrence River during the siege of Quebec, which brought him to the attention of the Admiralty and the Royal Society. This acclaim came at a crucial moment for the direction of British overseas exploration, and it led to his commission in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Torbern Bergman
Torbern Olaf (Olof) Bergman (''KVO'') (20 March 17358 July 1784) was a Swedish chemist and mineralogist noted for his 1775 ''Dissertation on Elective Attractions'', containing the largest chemical affinity tables ever published. Bergman was the first chemist to use the A, B, C, etc., system of notation for chemical species. Early life and education Torbern was born on 20 March 1735, the son of Barthold Bergman and Sara Hägg. He enrolled at the University of Uppsala at age 17. His father wished him to read either law or divinity, while he himself was anxious to study mathematics and natural science; in the effort to please both himself and his father, he overworked himself and harmed his health. During a period of enforced abstinence from study, he amused himself with field botany and entomology. He was able to send Linnaeus specimens of several new kinds of insects, and in 1756 he succeeded in proving that, contrary to the opinion of that naturalist, the so-called ''Coccus aqua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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