Solar System, technical/Venus

It is known as a common fact, Venus is the second planet in terms of proximity towards the Sun. Venus is also known as the Morning or the Evening star due to the fact that it is the brightest right before sunrise or a little after sunset. Venus is also known as the Earth's 'sister planet' because of its diameter, size, and bulk composition as it is nearly same as the earth's. Venus shines very well in night sky as its atmosphere is very thick and it reflects sunlight very brightly. Venus is also the hottest planet in our solar system. This is also because of its atmosphere. Its atmosphere mainly consists of sulphuric acid and carbon dioxide (CO2) that traps heat of the Sun and do not let it go back. Venus has no moons. It has a surface temperature of about 450℃~470℃ . Venus is the only planet named after a female figure. Statistics and other important informations about Venus are given below.

An ultraviolet image of the planet Venus is taken on February 26, 1979, by the Pioneer Venus Orbiter. Credit: NASA.
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Some information about the planet edit

  • Day (time taken to spin round its orbit): 243 Earth days
  • Year (time taken to cover its orbit): 224.7 Earth days
  • Diameter (at equator) : 12,102 km
  • Temperature: 450℃~470℃.
  • Distance from Sun: 107 million km~109 million km
  • Spacecraft from earth: Magellan orbiter (which reached Venus in 1980s)
Venus as the Evening Star, next to a crescent moon

Orbital characteristics edit

  • Aphelion: 108,942,109 km (0.72823128 AU)
  • Perihelion: 107,476,259 km (0.71843270 AU)
  • Semi-major axis: 108,208,930 km (0.723332 AU)
  • Eccentricity: 0.0068
  • Orbital period: 224.70069 day (0.6151970 yr)
  • Synodic period: 583.92 days
  • Avg. orbital speed: 35.02 km/s
  • Inclination: 3.39471° (3.86° to Sun's equator)
  • Longitude of ascending node: 76.67069°
  • Argument of perihelion: 54.85229°
  • Satellites: None

Physical characteristics edit

  • Mean radius: 6051.8 ± 1.0 km (0.9499 Earths)
  • Flattening: < 0.0002
  • Surface area: 4.60×108 km² (0.902 Earths)
  • Volume: 9.38×1011 km³ (0.857 Earths)
  • Mass: 4.8685×1024 kg (0.815 Earths)
  • Mean density: 5.204 g/cm³
  • Equatorial surface gravity: 8.87 m/s2 (0.904 g)
  • Escape velocity: 10.46 km/s
  • Sidereal rotation period: −243.0185 day
  • Rotation velocity at equator: 6.52 km/h
  • Axial tilt: 177.36°
  • Right ascension of North pole: 18 hours, 11 minutes, 2 seconds (272.76°)
  • Declination of North pole: 67.16°
  • Albedo: 0.65
  • Surface temp.:

Kelvin: 735K Celsius: 461.85℃

  • Apparent magnitude: up to -4.6
  • Angular diameter: 9.7" — 66.0"
  • Adjectives: Venusian or (rarely) Cytherean

Atmosphere edit

  • Surface pressure: 9.3 MPa
  • Composition:
  1. ≈ 96.5% Carbon dioxide
  2. ≈ 3.5% Nitrogen
  3. 0.015% Sulphur dioxide
  4. 0.007% Argon
  5. 0.002% Water vapor
  6. 0.0017% Carbon monoxide
  7. 0.0012% Helium
  8. 0.0007% Neon
  9. Trace Carbonyl sulfide
  10. Trace Hydrogen chloride
  11. Trace Hydrogen fluoride

Meteor astronomy edit

In visual astronomy "[a]lmost no variation or detail can be seen in the clouds. ... The surface is obscured by a thick blanket of clouds. ... Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. ... [It has] thick clouds of sulfur dioxide ... [There are] lower and middle cloud layers ... [The] thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets.[1][2] These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of the Venusian surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, the Venusian surface is not as well lit."[3]

"Strong 300 km/h winds at the cloud tops circle the planet about every four to five earth days.[4] Venusian winds move at up to 60 times the speed of the planet's rotation, while Earth's fastest winds are only 10% to 20% rotation speed.[5]"[3]

"Average cloud-top wind speeds on Venus rose 33 percent between 2006 and 2012, jumping from 186 mph (300 km/h) to 249 mph (400 km/h), observations by Europe's Venus Express orbiter show."[6]

"This is an enormous increase in the already high wind speeds known in the atmosphere, ... Such a large variation has never before been observed on Venus, and we do not yet understand why this occurred."[7]

The wind speeds are determined "by studying images captured by Venus Express between [50° N and S latitude, and tracking] the movements of tens of thousands of feature in the cloud tops some [70 km] above the planet's surface."[6]

"Our analysis of cloud motions at low latitudes in the southern hemisphere showed that over the six years of study the velocity of the winds changed by up 70 km/h over a time scale of 255 Earth days — slightly longer than a year on Venus".[8]

"Sometimes clouds took 3.9 days to zip all the way around Venus, for example, while on other occasions the journey required 5.3 days."[6]

"Although there is clear evidence that the average global wind speeds have increased, further investigations are needed in order to explain what drives the atmospheric circulation patterns that are responsible, and to explain the changes seen in localized areas on shorter timescales ... The atmospheric super-rotation of Venus is one of the great unexplained mysteries of the solar system ... These results add more mystery to it, as Venus Express continues to surprise us with its ongoing observations of this dynamic, changing planet."[9]

"Venus has a super-rotating atmosphere that whips around the planet once every four Earth days; Venus itself takes 243 Earth days to complete one rotation."[6]

X-ray astronomy edit

This Chandra X-ray Observatory image is the first X-ray image ever made of Venus. Credit: NASA/MPE/K.Dennerl et al..

The first ever X-ray image of Venus is shown at right. The "half crescent is due to the relative orientation of the Sun, Earth and Venus. The X-rays from Venus are produced by fluorescent radiation from oxygen and other atoms in the atmosphere between 120 and 140 kilometers above the surface of the planet. In contrast, the optical light from Venus is caused by the reflection from clouds 50 to 70 kilometers above the surface. Solar X-rays bombard the atmosphere of Venus, knock electrons out of the inner parts of atoms, and excite the atoms to a higher energy level. The atoms almost immediately return to their lower energy state with the emission of a fluorescent X-ray. A similar process involving ultraviolet light produces the visible light from fluorescent lamps."[10]

Ultraviolet astronomy edit

Mariner 10 false color UV Venus image has been processed from Clear and Blue and UV filters. Credit: Ricardo Nunes.

When imaged in the ultraviolet (article top right), Venus appears like a gas dwarf object rather than a rocky object.

The image on the right has been re-processed through the clear, blue, and UV filters of Mariner 10 from the image taken of Venus by Mariner 10 on May 5, 1974, to show greater detail.

Visual astronomy edit

This is an image of Venus in true color. The surface is obscured by a thick blanket of clouds. Credit: NASA/Ricardo Nunes,

When imaged in visible light (left) Venus appears like a gas dwarf rather than a rocky body. The same image result occurs when it is viewed in the ultraviolet (right at page top).

Violets edit

Violet photographs of the planet Venus taken in 1927 “recorded two nebulous bright streaks, or bands, running ... approximately at right angles to the terminator” that may be from the upper atmosphere.[11]

Green astronomy edit

"Venus at times shows [the oxygen] green line emission with an intensity equal to terrestrial values [Slanger et al., 2001]. Furthermore, the intensity is quite variable, as is true for the much stronger O2( a-X) 1.27 μ emission."[12]

"In 1999, observations of the Venus nightglow with the Keck I telescope showed that the 5577 Å oxygen green line was a significant feature, comparable in intensity to the terrestrial green line. Subsequent measurements have been carried out at the Apache Point Observatory (APO) and again at Keck I, confirming the presence of the line with substantially varying intensity."[13]

"Ground-based studies suggest that the [557.7 nm oxygen green line] emission is correlated with the solar cycle."[14]

Infrareds edit

This is a false-color near-infrared image of lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990. Credit: NASA/JPL.

"The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)-X(v″) progression more than 3 decades ago."[15]

"Spectroscopic observations of the differential Doppler shift in a CO2 absorption line on Venus show that the upper atmospheric wind near the equator appears to have both a retrograde motion of about -85 ± 10 m s-1 ... and ... a periodically varying component, with an amplitude of about 40 ± 14 m s-1 and a period of 4.3 ± 0.2 days."[16]

At right is a false-color near-infrared image of the lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990.

"Bright slivers of sunlit high clouds are visible above and below the dark, glowing hemisphere. The spacecraft is about 100,000 kilometers (60,000 miles) above the planet. An infrared wavelength of 2.3 microns (about three times the longest wavelength visible to the human eye) was used. The map shows the turbulent, cloudy middle atmosphere some 50-55 kilometers (30- 33 miles) above the surface, 10-16 kilometers or 6-10 miles below the visible cloudtops. The red color represents the radiant heat from the lower atmosphere (about 400 degrees Fahrenheit) shining through the sulfuric acid clouds, which appear as much as 10 times darker than the bright gaps between clouds. This cloud layer is at about -30 degrees Fahrenheit, at a pressure about 1/2 Earth's surface atmospheric pressure. Near the equator, the clouds appear fluffy and blocky; farther north, they are stretched out into East-West filaments by winds estimated at more than 150 mph, while the poles are capped by thick clouds at this altitude."[17]

Radio astronomy edit

Using an imaging radar technique, the Magellan spacecraft was able to lift the veil from the face of Venus and produce this spectacular high resolution image of the planet's surface. Red, in this false-color map, represents mountains, while blue represents valleys. Credit: Magellan Team, JPL, NASA.
This is a false color image of Venus produced from a global radar view of the surface by the Magellan probe while radar imaging between 1990-1994. Credit: NASA.

"The first un-ambiguous detection of Venus was made by [the] Jet Propulsion Laboratory (JPL) on 10 March 1961. A correct measurement of the AU soon followed."[18]

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."[19]

When viewed using radio astronomy, the resulting radar image, at left, shows that just beneath the cloud layers is a rocky object.

Gaseous objects edit

Venus has been detected as a gaseous object using X-ray through red astronomy.

Atmospheric astronomy edit

The image shows Venus Express data with an artist's impression of the tear-drop shaped ionosphere. Credit: ESA/Wei et al. (2012).

"During a rare period of very low density solar outflow, the ionosphere of Venus was observed to become elongated downstream, rather like a long-tailed comet. ... Under normal conditions, the solar wind has a density of 5 - 10 particles per cubic cm at Earth's orbit, but occasionally the solar wind almost disappears, as happened in May 1999. ... A rare opportunity to examine what happens when a tenuous solar wind arrives at Venus came 3 - 4 August 2010, following a series of large coronal mass ejections on the Sun. NASA's STEREO-B spacecraft, orbiting downstream from Venus, observed that the solar wind density at Earth's orbit dropped to the remarkably low figure of 0.1 particles per cubic cm and persisted at this value for an entire day."[20]

"The observations show that the night side ionosphere moved outward to at least 15 000 km from Venus' centre over a period of only a few hours," said Markus Fraenz, also from the Max Planck Institute for Solar System Research, who was the team leader and a co-author of the paper.[20] "It may possibly have extended for millions of kilometres, like an enormous tail."[20]

"Although we cannot determine the full length of the night-side ionosphere, since the orbit of Venus Express provides limited coverage, our results suggest that Venus' ionosphere resembled the teardrop-shaped ionosphere found around comets, rather than the more symmetrical, spherical shape which usually exists."[20]

"The side of Venus' ionosphere that faces away from the sun can billow outward like the tail of a comet, while the side facing the star remains tightly compacted, researchers said. ... "As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions," ESA officials said in a statement today (Jan. 29). It only takes 30 to 60 minutes for the planet's comet-like tail to form after the solar wind dies down. Researchers observed the ionosphere stretch to at least 7,521 miles (12,104 kilometers) from the planet, said Yong Wei, a scientist at the Max Planck Institute in Katlenburg, Germany who worked on this research."[21]

"[B]ecause of the lack of a planetary magnetic field, the free hydrogen has been swept into interplanetary space by the solar wind.[22]"[3]

"The clouds of Venus are capable of producing lightning much like the clouds on Earth.[23] The existence of lightning had been controversial since the first suspected bursts were detected by the Soviet Venera probes. In 2006–07 Venus Express clearly detected whistler mode waves, the signatures of lightning. Their intermittent appearance indicates a pattern associated with weather activity. The lightning rate is at least half of that on Earth.[23] In 2007 the Venus Express probe discovered that a huge double atmospheric vortex exists at the south pole of the planet.[24][25]"[3]

"Another discovery made by the Venus Express probe in 2011 is that an ozone layer exists high in the atmosphere of Venus.[26]"[3]

"Venus has an extremely dense atmosphere, which consists mainly of carbon dioxide and a small amount of nitrogen. The atmospheric mass is 93 times that of Earth's atmosphere, while the pressure at the planet's surface is about 92 times that at Earth's surface—a pressure equivalent to that at a depth of nearly 1 kilometer under Earth's oceans. The density at the surface is 65 kg/m³ (6.5% that of water)."[3]

Magnetohydrodynamics edit

"In 1967, Venera-4 found the Venusian magnetic field is much weaker than that of Earth. This magnetic field is induced by an interaction between the ionosphere and the solar wind,[27][28] ... Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation. This radiation may result in cloud-to-cloud lightning discharges.[29]"[3]

"The weak magnetosphere around Venus means the solar wind is interacting directly with the outer atmosphere of the planet. Here, ions of hydrogen and oxygen are being created by the dissociation of neutral molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape the planet's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, while higher-mass molecules, such as carbon dioxide, are more likely to be retained."[3]

Meteorites edit

"While there is little or no water on Venus, there is a phenomenon which is quite similar to snow. The Magellan probe imaged a highly reflective substance at the tops of Venus's highest mountain peaks which bore a strong resemblance to terrestrial snow. This substance arguably formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gas form to cooler higher elevations, where it then fell as precipitation. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena).[30]"[31]

Crater astronomy edit

Impact craters on the surface of Venus (image reconstructed from radar data) are shown. Credit: .

"The absence of evidence of lava flow accompanying any of the visible caldera remains an enigma. The planet has few impact craters".[3]

"After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne.[32][33]"[3]

"Almost a thousand impact craters on Venus are evenly distributed across its surface. ... On Venus, about 85% of the craters are in pristine condition. ... Venusian craters range from 3 km to 280 km in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere, they do not create an impact crater.[34] Incoming projectiles less than 50 meters in diameter will fragment and burn up in the atmosphere before reaching the ground.[35]"[3]

Classical planets edit

The Venus tablet of Ammisaduqa, dated 1581 BC, records the observations of Babylonian astronomers. It refers to Venus as Nin-dar-an-na, or "bright queen of the sky". Credit: .

The day of the week for Venus is Friday and its color is white.[36]

5102 b2k, -3102 or 3102 BC, is the historical year assigned to a Hindu table of planets that does not include the classical planet Venus.[37] "Vénus seule ne s'y trouvait pas."[37] "Venus alone is not found there."[38] "Babylonian astronomy, too, had a four-planet system. In ancient prayers the planets Saturn, Jupiter, Mars, and Mercury are invoked; the planet Venus is missing; and one speaks of "the four-planet system of the ancient astronomers of Babylonia."[39]"[38]

“That the planet Venus is missing will not startle anybody who knows the eminent importance of the four-planet system in the Babylonian astronomy”[39] “Weidner supposes that Venus is missing in the list of planets because “she belongs to a triad with the moon and the sun.””[38]

3581 b2k: "The Venus tablet of Ammisaduqa, dated 1581 BC, shows that the Babylonians understood that the two were a single object, referred to in the tablet as the "bright queen of the sky," and could support this view with detailed observations.[40]"[3]

"The Greeks thought of the two as separate stars, Phosphorus and Hesperus, until the time of Pythagoras in the sixth century BC.[41]"[3]

"The Romans designated the morning aspect of Venus as Lucifer, literally "Light-Bringer", and the evening aspect as Vesper"[3].

See also edit

References edit

  1. Krasnopolsky, V. A.; Parshev, V. A. (1981). "Chemical composition of the atmosphere of Venus". Nature 292 (5824): 610–613. doi:10.1038/292610a0. 
  2. Vladimir A. Krasnopolsky (2006). "Chemical composition of Venus atmosphere and clouds: Some unsolved problems". Planetary and Space Science 54 (13–14): 1352–1359. doi:10.1016/j.pss.2006.04.019. 
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 "Venus, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. March 18, 2013. Retrieved 2013-04-03. Cite error: Invalid <ref> tag; name "Venus" defined multiple times with different content
  4. W. B., Rossow; A. D., del Genio; T., Eichler (1990). "Cloud-tracked winds from Pioneer Venus OCPP images" (PDF). Journal of the Atmospheric Sciences 47 (17): 2053–2084. doi:10.1175/1520-0469(1990)047<2053:CTWFVO>2.0.CO;2. ISSN 1520-0469. 
  5. Normile, Dennis (7 May 2010). "Mission to probe Venus's curious winds and test solar sail for propulsion". Science 328 (5979): 677. doi:10.1126/science.328.5979.677-a. PMID 20448159. 
  6. 6.0 6.1 6.2 6.3 Mike Wall (June 19, 2013). "Mystery on Venus: 'Super-Hurricane' Force Winds Inexplicably Get Stronger". Yahoo! News. Retrieved 2013-06-20.
  7. Igor Khatuntsev (June 19, 2013). "Mystery on Venus: 'Super-Hurricane' Force Winds Inexplicably Get Stronger". Yahoo! News. Retrieved 2013-06-20.
  8. Toru Kouyama (June 19, 2013). "Mystery on Venus: 'Super-Hurricane' Force Winds Inexplicably Get Stronger". Yahoo! News. Retrieved 2013-06-20.
  9. Håkan Svedhem (June 19, 2013). "Mystery on Venus: 'Super-Hurricane' Force Winds Inexplicably Get Stronger". Yahoo! News. Retrieved 2013-06-20.
  10. K. Dennerl (November 29, 2001). "Venus: Venus in a New Light". Boston, Massachusetts, USA: Harvard University, NASA. Retrieved 2012-11-26.
  11. W. H. Wright (August 1927). "Photographs of Venus made by Infra-red and by Violet Light". Publications of the Astronomical Society of the Pacific 39 (230): 220-1. doi:10.1086/123718. 
  12. T. G. Slanger (December 2005). "Practicality of Using Oxygen Atom Emissions to Evaluate the Habitability of Extra-Solar Planets". American Geophysical Union, Fall Meeting 2005. 
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  14. Tom G. Slanger; Nancy J. Chanover; Brian D. Sharpee; Thomas A. Bida (February 2012). "O/O2 emissions in the Venus nightglow". Icarus 217 (2): 845-8. doi:10.1016/j.icarus.2011.03.031. Retrieved 2013-01-20. 
  15. A. García Muñoz; F. P. Mills; T. G. Slanger; G. Piccioni; P. Drossart (December 2009). "Visible and near-infrared nightglow of molecular oxygen in the atmosphere of Venus". Journal of Geophysical Research: Planets 114 (E12). doi:10.1029/2009JE003447. Retrieved 2013-01-16. 
  16. W. A. Traub; N. P. Carleton (January 1, 1979). "Retrograde winds on Venus - Possible periodic variations". The Astrophysical Journal 227 (1): 329-33. doi:10.1086/156734. 
  17. Sue Lavoie (January 29, 1996). "PIA00124: Infrared Image of Low Clouds on Venus". Pasadena, California, USA: NASA/JPL. Retrieved 2013-01-20.
  18. "Radar astronomy, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. July 30, 2012. Retrieved 2012-08-30.
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  20. 20.0 20.1 20.2 20.3 Yong Wei; Markus Fraenz; Håkan Svedhem (January 29, 2013). "The tail of Venus and the weak solar wind". European Space Agency. Retrieved 2013-02-01.
  21. Miriam Kramer (January 31, 2013). "Venus Can Have 'Comet-Like' Atmosphere". Yahoo! News. Retrieved 2013-01-31.
  22. "Caught in the wind from the Sun". ESA (Venus Express). 28 November 2007. Retrieved 2008-07-12.
  23. 23.0 23.1 S. T. Russell; T. L. Zhang; M. Delva; W. Magnes; R. J. Strangeway; H. Y. Wei (2007). "Lightning on Venus inferred from whistler-mode waves in the ionosphere". Nature 450 (7170): 661–662. doi:10.1038/nature05930. PMID 18046401. 
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  26. "ESA finds that Venus has an ozone layer too". ESA. 6 October 2011. Retrieved 2011-12-25.
  27. Dolginov, Nature of the Magnetic Field in the Neighborhood of Venus, Cosmic Research, 1969
  28. Kivelson G. M.; Russell C. T. (1995). Introduction to Space Physics. Cambridge University Press. ISBN 0-521-45714-9. 
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  30. Carolyn Jones Otten (2004). "'Heavy metal' snow on Venus is lead sulfide". Washington University in St Louis. Retrieved 2007-08-21.
  31. "Snow. In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. February 12, 2013. Retrieved 2013-02-16.
  32. "USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE)". Retrieved 22 October 2009.
  33. "The Magellan Venus Explorer's Guide". Retrieved 22 October 2009.
  34. R. R. Herrick, R. J. Phillips (1993). "Effects of the Venusian atmosphere on incoming meteoroids and the impact crater population". Icarus 112 (1): 253–281. doi:10.1006/icar.1994.1180. 
  35. David Morrison (2003). The Planetary System. Benjamin Cummings. ISBN 0-8053-8734-X. 
  36. Lloyd D. Graham (Summer 2010). "The Seven Seals of Revelation and the Seven Classical Planets". The Esoteric Quarterly 6: 45-58.,3. Retrieved 2012-05-21. 
  37. 37.0 37.1 Jean Baptiste Joseph Delambre (1817). Histoire de l'astronomie ancienne. Paris: Courcier. pp. 639. Retrieved 2012-01-13. 
  38. 38.0 38.1 38.2 Immanuel Velikovsky (January 1965). Worlds in Collision. New York: Dell Publishing Co., Inc.. pp. 401. Retrieved 2012-01-13. 
  39. 39.0 39.1 Ernst Friedrich Weidner (1915). Handbuch der babylonischen Astronomie, Volume 1. J. C. Hinrichs. pp. 146. Retrieved 2012-03-30. 
  40. Bartel Waerden (1974). Science awakening II: the birth of astronomy. Springer. p. 56. ISBN 9001931030. Retrieved 2011-01-10. 
  41. Pliny the Elder (1991). Natural History II:36–37. translated by John F. Healy. Harmondsworth, Middlesex, UK: Penguin. pp. 15–16. 

Further reading edit

External links edit

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