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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 second contact, and again just before third contact during the transit, a small black "teardrop" appears to connect Venus's disc to the 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. Observing Mercury simultaneously during its transit in May 1832 with different instru ... [...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 ... [...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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
James Cook
James Cook (7 November 1728Old 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] |
Royal Observatory, Greenwich
The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to Herstmonceux) is an observatory situated on a hill in Greenwich Park in south east London, overlooking the River Thames to the north. It played a major role in the history of astronomy and navigation, and because the Prime Meridian passes through it, it gave its name to Greenwich Mean Time, the precursor to today's Coordinated Universal Time (UTC). The ROG has the IAU observatory code of 000, the first in the list. ROG, the National Maritime Museum, the Queen's House and the clipper ship '' Cutty Sark'' are collectively designated Royal Museums Greenwich. The observatory was commissioned in 1675 by King Charles II, with the foundation stone being laid on 10 August. The old hilltop site of Greenwich Castle was chosen by Sir Christopher Wren, a former Savilian Professor of Astro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shuckburgh Telescope
The Shuckburgh telescope or Shuckburgh equatorial refracting telescope was a diameter aperture telescope on an equatorial mount completed in 1791 for Sir George Shuckburgh (1751–1804) in Warwickshire, England, and built by British instrument maker Jesse Ramsden (1735–1800)... The Shuckburgh telescope is described op. 99 It was transferred to the Royal Observatory, Greenwich in 1811 and the London Science Museum in 1929. Even though it has sometimes not been regarded as particularly successful, its design was influential. It was one of the larger achromatic doublet telescopes at the time, and one of the largest to have an equatorial mount. It was also known as the eastern equatorial for its location. It was pictured in the Rees Cyclopedia of the early 1800s. It was early pictured in ''Philosophical Transactions'', published in 1793. At the Royal Observatory in Greenwich, it was for a time installed in the North Dome, although this had a Sky view partially obscured by th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mercury (planet)
Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman god ' ( Mercury), god of commerce, messenger of the gods, and mediator between gods and mortals, corresponding to the Greek god Hermes (). Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and its apparent distance from the Sun as viewed from Earth never exceeds 28°. This proximity to the Sun means the planet can only be seen near the western horizon after sunset or the eastern horizon before sunrise, usually in twilight. At this time, it may appear as a bright star-like object, but is more difficult to observe than Venus. From Earth, the planet telescopically displays the complete range of phases, similar to Venus and the Moon, which recurs over its synodic period of approximately 116 days. The synodic proximity of Mercury to Earth makes Mercury ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transit Of Venus
frameless, upright=0.5 A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus can be seen from Earth as a small black dot moving across the face of the Sun. The duration of such transits is usually several hours (the transit of 2012 lasted 6 hours and 40 minutes). A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than three times that of the Moon, Venus appears smaller, and travels more slowly across the face of the Sun, because it is much farther away from Earth. Transits of Venus are among the rarest of predictable astronomical phenomena. They occur in a pattern that generally repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. The periodicity is a reflection of the fact that the orbital periods ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friedrich Wilhelm Argelander
Friedrich Wilhelm August Argelander (22 March 1799 – 17 February 1875) was a German astronomer. He is known for his determinations of stellar brightnesses, positions, and distances. Life and work Argelander was born in Memel in the Kingdom of Prussia (now Klaipėda in Lithuania), the son of a father of Finnish descent, Johann Gottlieb Argelander, and German (Prussian) mother, Dorothea Wilhelmina Grünlingen. He studied with Friedrich Bessel, whose assistant he became in 1820, and obtained his Ph.D. in 1822 at University of Königsberg. From 1823 until 1837, Argelander was the head of the Finnish observatory, first in Turku and then in Helsinki. He then moved to Bonn, Germany. There he designed and built a new observatory at the University of Bonn with funding approved directly by King Frederick William IV whom Argelander had become friends with in his childhood. This lifelong friendship had started when the then crown prince temporarily lived in Argelander's parents house ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friedrich Bessel
Friedrich Wilhelm Bessel (; 22 July 1784 – 17 March 1846) was a German astronomer, mathematician, physicist, and geodesist. He was the first astronomer who determined reliable values for the distance from the sun to another star by the method of parallax. A special type of mathematical functions were named Bessel functions after Bessel's death, though they had originally been discovered by Daniel Bernoulli and then generalised by Bessel. Life and family Bessel was born in Minden, Westphalia, then capital of the Prussian administrative region Minden-Ravensberg, as second son of a civil servant into a large family. At the age of 14 Bessel was apprenticed to the import-export concern Kulenkamp at Bremen. The business's reliance on cargo ships led him to turn his mathematical skills to problems in navigation. This in turn led to an interest in astronomy as a way of determining longitude. Bessel came to the attention of a major figure of German astronomy at the time, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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