184 research outputs found
Notre article de synthèse: Que nous a appris la comète de Halley?
No full textComet Halley is already back in the outer solar system, forgotten by most of us. But the cometary specialists are still busy with the wealth of data gathered during a few months of frantic activity, peaking with the spacecraft fly-bys. The author summarizes here some of the new results which have been obtained up to now about P/Halley
On the use of satellite observations to fill gaps in the Halley station total ozone record
No full textMeasurements by the Dobson ozone spectrophotometer at the British Antarctic Survey's (BAS) Halley research station form a record of Antarctic total column ozone that dates back to 1956. Due to its location, length, and completeness, the record has been, and continues to be, uniquely important for studies of long-term changes in Antarctic ozone. However, a crack in the ice shelf on which it resides forced the station to abruptly close in February of 2017, leading to a gap of two ozone hole seasons in its historic record. We develop and test a method for filling in the record of Halley total ozone by combining and adjusting overpass data from a range of different satellite instruments. Comparisons to the Dobson suggest that our method reproduces monthly ground-based total ozone values with an average difference of 1.1 ± 6.2 DU for the satellites used to fill in the 2017–2018 gap. We show that our approach more closely reproduces the Dobson measurements than simply using the raw satellite average or data from a single satellite instrument. The method also provides a check on the consistency of the provisional data from the automated Dobson used at Halley after 2018 with earlier manual Dobson data and suggests that there were likely inconsistencies between the two. The filled Halley dataset provides further support that the Antarctic ozone hole is healing, not only during September but also in January
Color gradients in the coma of P/Halley
No full textSome important information relevant to the understanding of the gas/dust dynamics near the surface of a comet nucleus concerns knowledge of the grain composition and scattering properties as well as the particle size distribution of dust in the coma. Ground based measurements of light scattered from the dust comae can provide some information about the physical grain properties, in particular about the mean optically dominant grain size. Optical spectra of continua of nine comets presented by Jewitt and Meech, 1986, show that all of the scattered light is reddened with respect to the Sun. There is significant scatter in the amount of reddening seen for different comets. In the near IF regions, the reddening decreases until near 2 to 3 micrometers where the reflectivity is nearly neutral. It is of particular interest to see if there are any observable changes in the grain size distribution during outburst. Although no coma colar changes were observed during the Nov. 1985 outbursts, a color gradient within the coma has been observed in Halley. Radial color gradients in J, H, and K images of Halley as reported by Campins have not been observed by the author
Convergence regions for the Chebyshev–Halley family
No full textIn this paper we study the dynamical behavior of the Chebyshev–Halley methods on the family of degree n polynomials . We prove that, despite increasing the degree, it is still possible to draw the parameter space by using the orbit of a single critical point. For the methods having as an attracting fixed point, we show how the basins of attraction of the roots become smaller as the value of n grows. We also demonstrate that, although the convergence order of the Chebyshev–Halley family is 3, there is a member of order 4 for each value of n.
In the case of quadratic polynomials, we bound the set of parameters which correspond to iterative methods with stable behaviour other than the basins of attraction of the roots
Methods and results for estimating the hydraulic characteristics of the subsurface materials in the Harney Basin, Oregon
No full textGerald H. Grondin, Darrick E. Boschmann, Halley J. Schibel, Benjamin P. Scandella.Title from PDF cover (viewed on December 20, 2021).This archived document is maintained by the State Library of Oregon as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Includes bibliographical references (pages 56-63).Mode of access: Internet from the Oregon Government Publications Collection.Text in English
A chart of the ocean between South America and Africa with the tracks of Dr. Edmund Halley in 1700 and Monsr. Lozier Bouvet in 1738 [cartographic material] /
No full textMap of the South Atlantic Ocean flanked by South America on the left and Africa on the right. The map features the time-dated sea-tracks of 18th century explorers Edmund Halley in command of HM Pink Paramore and later Lozier Bouvet in command of the Eagle and the Mary.; Imprint on map: Published according to Act of Parliament, April 1769.; Prime meridian: Greenwich.; From: A collection of voyages chiefly in the South Atlantick Ocean / Alexander Dalrymble. London : Printed for the author; sold by J. Nourse, 1775.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.map-rm461
Halley's Method as the First Member of an Infinite Family of Cubic Order Rootfinding Methods
No full textFor each natural number m ≥ 3, we give a rootfinding method Hm, with cubic order of convergence for simple roots. However, for quadratic polynomials the order of convergence of Hm is m. Each Hm depends on the input, the corresponding function value, as well as the first two derivatives. We shall refer to this family as Halley Family, since H3 is the well-known method of Halley. For all m ≥ 4, the asymptotic error constant of Hm is the same constant. Each Hm is described in terms of determinants that are computable recursively. The Halley Family and their derivative-free variants offer alternatives to the traditional rootfinding methods, such as secant, Newton, and Muller methods, as well as Halley’s method itself.Technical report DCS-TR-37
Preliminary report of glaciological study at Brunt Ice Shelf near Halley Base, Antarctica in January 1982
No full textGlaciological work was done on the Brunt Ice Shelf near Halley Base in January 1982 by the author who participated in the British Antarctic Survey as an exchanging scientist. Preliminary results of 1.75m pit work and the analysis of a 22m long core obtained with a microdrill system indicate (1) the seasonal variation in acidity of snow, (2) the average annual balance of 41.6g・cm^・a^ and (3) the depth hoar development in autumn. Further analysis of samples, such as microparticle concentration, gross β activity, δ^O and chemical component, and the climatological interpretation will clarify the process of atmospheric transportation of materials to the Brunt Ice Shelf, the Antarctic coast in the Atlantic sector
A Estrela de Belém
No full textIn this year of the Halley Comet, the author examines the different hypotheses,through the science light, that can explain what the Bethlehem star really was about which the Evangels speak to us. No ano do cometa Halley, o Autor examina as várias hipóteses que, à luz da Ciência, podem explicar o que realmente foi a "estrela de Belém” de que nos falam os Evangelhos. 
Effects of 2010 Hurricane Earl amidst geologic evidence for greater overwash at Anegada, British Virgin Islands
No full text© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Advances in Geosciences 38 (2014): 21-30, doi:10.5194/adgeo-38-21-2014.A post-hurricane survey of a Caribbean island affords comparisons with geologic evidence for greater overwash at the same place. This comparison, though of limited application to other places, helps calibrate coastal geology for assessment of earthquake and tsunami potential along the Antilles Subduction Zone.
The surveyed island, Anegada, is 120 km south of the Puerto Rico Trench and is near the paths of hurricanes Donna (1960) and Earl (2010), which were at or near category 4 when at closest approach. The survey focused on Earl's geologic effects, related them to the surge from Hurricane Donna, and compared them further with erosional and depositional signs of southward overwash from the Atlantic Ocean that dates to 1200–1450 AD and to 1650–1800 AD. The main finding is that the geologic effects of these earlier events dwarf those of the recent hurricanes.
Hurricane Earl's geologic effects at Anegada, observed mainly in 2011, were limited to wrack deposition along many of the island's shores and salt ponds, accretion of small washover (spillover) fans on the south shore, and the suspension and deposition of microbial material from interior salt ponds. Earl's most widespread deposit at Anegada, the microbial detritus, was abundantly juxtaposed with evidence for catastrophic overwash in prior centuries. The microbial detritus formed an extensive coating up to 2 cm thick that extended into breaches in beach-ridge plains of the island's north shore, onto playas that are underlain by a sand-and-shell sheet that extends as much as 1.5 km southward from the north shore, and among southward-strewn limestone boulders pendant to outcrops as much as 1 km inland. Earl's spillover fans also contrast with a sand-and-shell sheet, which was dated previously to 1650–1800, by being limited to the island's south shore and by extending inland a few tens of meters at most.
These findings complement those reported in this issue by Michaela Spiske and Robert Halley (Spiske and Halley, 2014), who studied a coral-rubble ridge that lines part of Anegada's north shore. Spiske and Halley attribute the ridge to storms that were larger than Earl. But they contrast the ridge with coral boulders that were scattered hundreds of meters inland by overwash in 1200–1450
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