See also Nutation in plants Image Praezession.png thumb 170px Rotation green , Precession blue and Nutation in obliquity red of the Earth Nutation from Latin n t re , to nod is a rocking, swaying, or nodding ... nutation is a movement of a rotational axis such that the first Euler angles Euler rotations Euler angle precession is constant. Astronomy The nutation of a planet happens because of tidal force s that cause ... is not constant. The nutation of the Earth s rotation axis of the Earth was discovered in 1728 by the British astronomer James Bradley , but this nutation was not explained in detail until ... to the ecliptic . The component that works along the ecliptic is known as the nutation in longitude . The component perpendicular to the ecliptic is known as the nutation in obliquity . Celestial coordinate ... both by precession of the equinoxes and nutation, and thus depend on the theories applied to precession and nutation, and on the date used as a reference date for the coordinate system. In simpler terms, nutation and precession values are important in observation from Earth for calculating the apparent ... Zaragoza Victoria, Km 27 800.jpg thumb 240px Nutation makes a small change to the angle at which ... and Moon , which continuously change location relative to each other and thus cause nutation in Earth s axis. The largest component of Earth s nutation has a period of 18.6 years, the same as that of the precession ... description set of equations that represents nutation is called a theory of nutation see, e.g., http ... Earth. Values The principal term of nutation is due to the regression of the moon s nodal line ... reason they seem to avoid the range from 34.8 to 91 days, so it is customary to split the nutation ... motion of the sacral base is called nutation, and the posterior motion is counter nutation. ref cite ... Fixation, Nutation, and Respect ref External links http www.engineersedge.com instrumentation nutating ... Nutace de Nutation Astronomie et Nutatsioon es Nutaci n eu Nutazio fr Nutation gl Nutaci n ko it Nutazione ... more details
unreferenced date December 2011 Free nutation is a kind of motion that can occur for a spinning object that is not a sphere . See also Free core nutation Chandler wobble physics stub Category Rotation ... more details
Nutation, in plants , is the bending movements executed by some plant organ s, such as stems, leaves, roots, etc., by which the part is inclined successively in various directions. ref name int incorporate NIE ref Nutations are due to the unequal rate of growth of different sides of the organ, an inequality which, so far as is known at present c. 1915 , is dependent upon internal unknown causes and is not called forth by the action of external stimuli. The word is often used in a broad sense in the phrase nutational movement , to include all the movements in plants caused by growth in contrast to variation movements or movements produced by reversible Turgor pressure turgor changes. ref name int incorporate Simple nutation occurs in dorsiventral organs, such as flat leaves, both foliage and floral. The movements are only in one plane, depending upon the unequal growth of the opposite sides. When young the growth of the foliage leaves is most rapid upon their outer dorsal face, in consequence of which the leaf applies itself to the axis, arches over the apex, and with its neighbors forms a compact bud. Later growth becomes more rapid on the inner ventral face, the bud opens, and the leaves straighten out. Similar inequality of growth, but more sharply localized, leads to the folding and rolling of the leaf in the bud. Like movements of radial organs, such as stems, cylindrical leaves, and roots, have been termed circumnutation, or revolving nutation, to distinguish them from the simple nutation of dorsiventral organs. When any plant is in vigorous growth the axis rarely grows in length uniformly on all sides. The side on which growth is most rapid will push the apex over towards ... stimuli . Thus twining plants exhibit both true nutation and nutation due to geotropic sensitiveness ... nutation of dorsiventral organs. Thus, the tulip , crocus , and other vernal flowers are very sensitive ... title Nutation of sunflower seedling accessdate 2010 12 29 Category Botany Nutation in plants ... more details
Year nav topic 1728 science The year 1728 in science and technology involved some significant events. Astronomy James Bradley uses stellar aberration first observed in 1725 in science 1725 to calculate the speed of light to be approximately 301 000 km s. ref name Delambre cite book first J. B. last Delambre authorlink Jean Baptiste Joseph Delambre title Histoire de l astronomie au dix huiti me si cle publisher Bachelier location Paris year 1827 ref James Bradley observes Nutation nutation of the Earth s axis . ref name Delambre Exploration July 14&ndash August 14 Vitus Bering sails northward from the Kamchatka Peninsula , through the Bering Strait , and rounds Cape Dezhnev . Physiology and medicine Pierre Fauchard publishes Le Chirurgien Dentiste, ou, Trait des Dents , the first comprehensive text on dentistry, including the first description of orthodontic braces. ref cite journal title The Birth of the Most Important 18th Century Dental Text Pierre Fauchard s Le Chirurgien Dentist first Andrew I. last Spielman url http jdr.sagepub.com content 86 10 922.full journal Journal of Dental Research doi 10.1177 154405910708601004 month October year 2007 volume 86 issue 10 pages 922 926 accessdate 2012 03 09 ref Births February 13 John Hunter surgeon John Hunter , Scottish people Scottish surgeon , pathologist and comparative anatomist d. 1793 in science 1793 March 20 Samuel Auguste Tissot , Swiss people Swiss physician d. 1797 in science 1797 April 16 Joseph Black , Scottish physicist and chemist d. 1799 in science 1799 September 3 Matthew Boulton , English people English mechanical engineer d. 1809 in science 1809 October 27 James Cook , English List of explorers explorer d. 1779 in science 1779 Deaths August 11 William Sherard , English botanist b. 1659 in science 1659 References reflist Category 1728 in science fr 1728 en science hu 1728 a tudom nyban mk 1728 sv Vetenskaps ret 1728 ... more details
Distinguish Procession Precession refers to a specific change in the direction of the rotation axis of a rotating object, in which the second Euler angle angle of nutation is constant Precession may specifically mean Precession is the name of one of the Euler angles Euler rotations Euler rotations Axial precession astronomy &mdash the precession of the Earth s axis of rotation also known as the precession of the equinoxes , or similar de Sitter precession &mdash a general relativistic correction to the precession of a gyroscope near a large mass such as the Earth Larmor precession &mdash the precession of the magnetic moments of electrons, atomic nuclei, and atoms about an external magnetic field Lense Thirring precession &mdash a general relativistic correction to the precession of a gyroscope near a large rotating mass such as the Earth Precession mechanical &mdash the process of one part rotating with respect to another due to fretting between the two Thomas precession &mdash a special relativistic correction to the precession of a gyroscope in a rotating non inertial frame Precession can also refer to change in the direction of an axis other than an axis of rotation Apsidal precession , perihelion precession, or orbital precession, the rotation of the orbit of a celestial body See also Axial tilt , also called axial inclination or obliquity, is the inclination angle of a planet s rotational axis in relation to a perpendicular to its orbital plane Conventional International Origin is a conventionally defined reference axis of the pole s average location over the year 1900 Great year , also known as a Platonic year or Equinoctial cycle, is the time required for one complete cycle of the precession of the equinoxes Nutation is a slight irregular motion etymologically a nodding in the axis of rotation of a largely axially symmetric object Polar motion is the movement of Earth s rotation axis across its surface disambig it Precessione disambigua lt Precesija reik m s ... more details
class infobox width 350 align center Image Union flag 1606 Kings Colors .svg 30px 1728 in Great Britain Image Union flag 1606 Kings Colors .svg 30px style background color f3f3f3 align center small Other years small align center 1726 in Great Britain 1726 1727 in Great Britain 1727 1728 1729 in Great Britain 1729 1730 in Great Britain 1730 style background color f3f3f3 align center small Sport small align center 1728 English cricket season Events from the year 1728 in Kingdom of Great Britain Great Britain . Incumbents Monarch George II of the United Kingdom King George II Prime Minister Robert Walpole , British Whig Party Whig Events 29 January First performance of John Gay s The Beggar s Opera . ref name Pocket On This Day cite book title Penguin Pocket On This Day publisher Penguin Reference Library isbn 0 14 102715 0 year 2006 ref March Spain ends its siege of Gibraltar . ref name Cassell s Chronology citebook last Williams first Hywel title Cassell s Chronology of World History location London publisher Weidenfeld & Nicolson year 2005 isbn 0 304 35730 8 ref Late Summer Voltaire ends his exile in England. September Astronomer James Bradley uses stellar aberration first observed in 1725 to calculate the speed of light . ref name Delambre cite book first J. B. last Delambre authorlink Jean Baptiste Joseph Delambre title Histoire de l astronomie au dix huiti me si cle publisher Bachelier location Paris year 1827 ref James Bradley observes Nutation nutation of the Earth s axis . ref name Delambre The King s son Frederick, Prince of Wales , arrives in Britain for the first time, aged 21. Probable date at which the brown rat first enters Britain. ref cite book authorlink John Berkenhout first John last Berkenhout year 1769 title Outlines of the Natural History of Great Britain ref Publications Ephraim Chambers Cyclopaedia, or Universal Dictionary of Arts and Sciences . ref name Cassell s Chronology James Gibbs A Book of Architecture, containing designs of buildings an ... more details
The Chandler wobble is a small motion in the Earth s axis of Earth rotation rotation relative to the Earth s surface, which was discovered by United States American astronomer Seth Carlo Chandler in 1891. It amounts to convert 9 m ft Citation needed date May 2011 on the Earth s surface and has a period of 433 days. This wobble combines with another wobble with a period of one year so that the total polar motion varies with a period of about 7 years. The Chandler wobble is an example of the kind of motion that can occur for a spinning object that is not a sphere this is called a free nutation . Somewhat confusingly, the direction of the Earth s spin axis relative to the stars also varies with different periods, and these motions caused by the tidal attraction of the Moon and Sun are also called nutation s, except for the slowest, which is the precession of the equinoxes . The existence of a free nutation of the Earth was predicted by Isaac Newton in Corollaries 20 to 22 of Proposition 66, Book 1 of the Philosophi Naturalis Principia Mathematica , and by Leonhard Euler in 1755 as part of his studies of the dynamics of rotating bodies. Based on the known flattening of the Earth he predicted that it would have a period of 305 days. Several astronomers searched for motions with this period, but none were found. Chandler s contribution was to look for motions at any possible period once the Chandler wobble was observed, the difference between its period and the one predicted by Euler was explained by Simon Newcomb as being caused by the non rigidity of the Earth. The full explanation for the period also involves the fluid nature of the Earth s core and oceans the wobble in fact produces a very small ocean tide with an amplitude of c. 6 mm, the pole tide , which is the only tide not caused by extraterrestrial bodies. Despite the small amplitude, the gravitational effect of the pole tide is easily detected by the gravimeter superconducting gravimeter see e.g. Fig. 2.3 ... more details
Precession is the rotation of a plane or its associated perpendicular axis with respect to a reference plane. The orbit of the Moon has two important such precessional motions. First, the long axis line of the apsides perigee and apogee of the Moon s elliptical orbit precession precess es Eastward about once in just under 9 years. It is caused by the Sun solar tide . This is the reason that an anomalistic month the period of time that the Moon moves from the perigee to the apogee and to the perigee again is longer than the sidereal month the period of time when the Moon completes one revolution with respect to the fixed stars . This apsidal precession completes one rotation in the same time as the number of sidereal month s exceeds the number of anomalistic month s by exactly one, after about 3233 days 8.85 years . This apsidal precession also causes the full moon cycle , which can be interpreted as the time for the Sun to make 1 revolution with respect to the lunar perigee, to be longer by almost 2 months than a sidereal year . There are approximately two such lunar apsidal precession cycles in a Saros cycle . Another precession is that of the lunar node s that is, the line along which the plane of the Moon s orbit and that of Earth s orbit intersect. This is mainly caused by the flattening of the Earth it is the period of the main nutation term in the orientation of the polar axis of the Earth. This nodal period is about twice as long about 18.6 years as the apsidal precession period discussed above, and the direction of motion is Westward. This is the reason that a draconic month the period of time that the Moon takes to return to the same node is shorter than the sidereal month. After one nodal precession period, the number of draconic months exceeds the number of sidereal months by exactly one. This period is about 6793 days 18.60 years . As a result of this nodal precession, the time for the Sun to return to the same node, the eclipse year , is about 18.623 da ... more details
Mikhail Sergeevich Molodenskii lang ru , OldStyleDate June 16 1909 June 3 November 12, 1991 was a famous Soviet Geodesic physical geodesist . He was once said to be probably the only geodesist who would have deserved a Nobel prize ref Helmut Moritz and M. I. Yurkina eds. , M. S. Molodensky in Memoriam , Mitteilungen der geod tischen Institute der Technischen, Universit t Graz, Folge 88, Graz, 2000, http www.helmut moritz.at SciencePage Molodensky.pdf ref He graduated from Moscow State University 1936 , since 1946 he worked for the Institute of Earth Physics . He created an original theory for determining of the Earth shape and its gravitational field based on the surface measurement, built the first Soviet gravimeter , developed a theory of the nutation of Earth. He won the Stalin Prize 1946 and 1951 and the Lenin Prize 1961 . His legacy includes the Molodensky transformations , which are commonly used to transform between Datum geodesy geodetic datums . References reflist External links ru icon http www.oval.ru enc 44028.html Large Soviet Enciclopedia on Molodensky he is probably the only geodesist who would have deserved a Nobel prize Persondata Metadata see Wikipedia Persondata . NAME Molodenskii, Mikhail ALTERNATIVE NAMES SHORT DESCRIPTION DATE OF BIRTH 1909 PLACE OF BIRTH DATE OF DEATH November 12, 1991 PLACE OF DEATH DEFAULTSORT Molodenskii, Mikhail Category Russian physicists Category Soviet physicists Category Russian geologists Category Soviet geologists Category Russian geodesists Category 1909 births Category 1991 deaths Category Moscow State University alumni Russia physicist stub geologist stub de Michail Sergejewitsch Molodenski pl Michai Mo odie ski ru , uk zh ... more details
Orphan date February 2009 In astrophysics , the Darwin Radau equation gives a relation between the third principal moment of inertia of the Earth and its rotational speed and shape. It is assumed that the rotating Earth is in hydrodynamic equilibrium and is an ellipsoid of revolution . The Darwin Radau equation states ref cite journal last Bourda first G coauthors Capitaine N year 2004 title Precession, nutation, and space geodetic determination of the Earth s variable gravity field journal Astronomy and Astrophysics volume 428 pages 691 702 doi 10.1051 0004 6361 20041533 bibcode 2004A&A...428..691B ref math frac C MR e 2 frac 2 3 lambda frac 2 3 left 1 frac 2 5 sqrt 1 eta right math where M and R sub e sub represent the mass and mean equatorial radius of the Earth. Here is the Jean le Rond d Alembert d Alembert parameter and the Rodolphe Radau Radau parameter is defined as math eta frac 5q 2 epsilon 2 math where q is the geodynamical constant math q frac omega 2 R e 3 GM approx 3.461391 times 10 3 math and is the geometrical flattening math epsilon frac R p R e R e math where R sub p sub is the mean polar radius of the Earth. References reflist 1 Category Astrophysics Category Earth physics stub ar ... more details
Jet damping or thrust damping is the effect of rocket exhaust removing energy from the transverse angular motion of a rocket. If a rocket has Flight dynamics pitch or Yaw angle yaw motion then the exhaust must be accelerated laterally as it flows down the exhaust tube and nozzle. Once the exhaust leaves the nozzle this lateral momentum is lost to the vehicle and thus serves to damping damp the lateral oscillations. The jet damping is stabilizing as long as the distance from the instantaneous spacecraft center of mass to the nozzle exit plane exceeds the instantaneous transverse radius of gyration . Most rocket or missile configurations meet this criteria and the jet damping has a dynamic stabilizing effect. The jet damping torque rotates at nutation frequency in the spacecraft frame ref cite journal last van der Ha first Jozef C. coauthors Janssens, Frank L. title Jet Damping and Misalignment Effects During Solid Rocket Motor Burn journal AIAA Guidance, Navigation, and Control Conference date 11 14 August 2003 Austin, Texas year 2003 ref . The jet damping contributes to the pitch and yaw damping coefficients, math Cm q math and math Cn r math , where math Cm q math is the rate of change of pitching moment with respect to pitch rate and math Cn r math is the rate of change of the yawing moment with respect to yaw rate. For jet airplanes in cruise, the contribution of jet damping is usually negligible because the external aerodynamic damping is large relative to the jet damping. Rockets at lift off, however, have practically zero external aerodynamic damping and the jet damping becomes significant ref cite book last Etkins first Bernard Reid, Lloyd Duff title Dynamics of Flight year 1996 publisher John Wiley & Sons, Inc. pages 141 ref . References Reflist Category Rocket propulsion ... more details
infobox software name SOFA software libraries latest release version 2009 12 31 latest release date 2010 01 27 programming language C programming language C and Fortran operating system Cross platform genre List of numerical analysis software Numerical library license SOFA Software License website http www.iausofa.org The SOFA Standards of Fundamental Astronomy software libraries are a collection of subroutines that implement official International Astronomical Union IAU algorithms for astronomy astronomical computations. As of February 2009 they are available in both Fortran and C programming language C source code format. Capabilities The subroutines in the libraries cover the following areas Calendars Time standard Time scales Earth s rotation and sidereal time Ephemerides limited precision Precession astronomy Precession , nutation , polar motion Proper motion Star catalog conversions Licensing As of the February 2009 release, SOFA Software license licensing changed to allow use for any purpose, provided certain requirements are met. ref citation title SOFA Software License for Issue 2009 02 01 url http www.iau sofa.rl.ac.uk 2009 0201 C sofa copyr.lis date 2008 09 30 accessdate 2009 09 09 publisher International Astronomical Union . ref Previously, commercial usage was specifically excluded and required written agreement of the SOFA board. ref citation title SOFA Software License for Issue 2008 03 01 url http www.iau sofa.rl.ac.uk 2008 0301 sofa copyr.lis date 2007 05 21 accessdate 2009 09 09 publisher International Astronomical Union . ref See also Naval Observatory Vector Astrometry Subroutines References reflist External links http www.iausofa.org SOFA Home Page http www.scholarpedia.org article Standards of Fundamental Astronomy Scholarpedia overview of SOFA http www.iau.org International Astronomical Union Category Celestial mechanics Category Celestial coordinate system Category Numerical software Category Astronomy software Astronomy stub compu library st ... more details
The Earth s rotation is not even. Any motion in on the Earth causes a slowdown or speedup of the rotation, or a change of rotation axis. Most of them can be ignored, but movements of very large mass, like sea current or tide can produce discernible changes and cause error to very precise astronomical observations. A single Parameter Mathematical functions parameter can be used to describe one phenomenon. The collection of Earth Orientation Parameters EOP is fitted to describe the rotation irregularities all together. Technically, they provide the rotation transforming the International Terrestrial Reference System ITRS to the International Celestial Reference System ICRS , or vice versa, as a function of time. Components Universal time . Universal time UT1 stands for the earth rotation, which performs one revolution in about 24h. The earth rotation is uneven, so UT is not linear with respect to atomic time . It is practically proportional to the sidereal time , which is also a direct measure of earth rotation. The excess revolution time is called length of day LOD . Coordinates of the pole . Due to the very slow pole motion of the earth, the Celestial Ephemeris Pole CEP, or celestial pole does not stick still on surface of earth. The Celestial Ephemeris Pole is calculated with past observation data, and is somehow averaged, so it differs from the instantaneous rotation axis by quasi diurnal terms, which are as small as under 0.01 see ref Seidelmann, P.K. 1982 Celest. Mech., 27, 79. ref . In setting up a coordinate system, a static terrestrial point called the IERS Reference Pole, or IRP, is used as origin the x axis is in the direction of IRM, the IERS Reference Meridian the y axis is in the direction 90 degrees West longitude . x and y are the coordinates of the CEP relative to the IRP. Celestial pole offsets . Celestial pole offsets are described in the IAU Precession and Nutation models. The observed differences with respect to the conventional celestial pole pos ... more details
The Ernst angle is the flip angle a.k.a. tip or nutation angle for a particular spin that gives the maximal signal in the least amount of time when signal averaging over many transients. This relationship was developed by Richard Ernst , winner of the 1991 Nobel Prize in Chemistry. ref cite web url http nobelprize.org nobel prizes chemistry laureates 1991 title 1991 Nobel Laureates in Chemistry ref ref cite journal doi 10.1063 1.1719961 title Application of Fourier transform spectroscopy to magnetic resonance year 1966 last1 Ernst first1 R. R. journal Review of Scientific Instruments volume 37 pages 93 ref The following equation relates the Ernst angle, theta, to the experimental interpulse delay, d1 the duration of the Free induction decay , aka acquisition time , or at and the T1 relaxation longitudinal relaxation time of the spin in question, T sub 1 sub math cos theta e d1 at T 1 math For example, if one wishes to get the best signal from a resonance with T sub 1 sub 3 sec, and one wishes to use d1 1sec and at 2sec, the optimal tip angle is 68 degrees. This relationship is especially important in Magnetic Resonance Imaging MRI , where interscan delays d1 and acquisition times at are often short relative to the signal s T sub 1 sub value. In MRI, there is typically just one resonance being observed H sub 2 sub O and the T sub 1 sub of H sub 2 sub O depends on its local environment. Note that d1 and at together may be referred to collectively as TR in the MRI community. math cos theta e TR T 1 math References reflist Category Nuclear magnetic resonance Category NMR spectroscopy Category Magnetic resonance imaging fa ... more details
of fundamental variables, such as the nutation angles and the heliocentric positions of solar system ... transformations , such as those caused by precession , nutation and aberration of light aberration ... more details
the east in the fundamental plane. Primary direction also Precession Nutation This description of the Orientation ... s axis, nutation . ref Explanatory Supplement 1961 , pp. 20, 28 ref In order to fix the exact ... , but free from the small periodic oscillations of nutation . Commonly used in planetary orbit calculation ... equator plus nutation . This is the actual intersection of the two planes at any particular ... time with the motions of precession and nutation . In astronomy ref Explanatory Supplement 1961 , pp ... and nutation , but it is otherwise equivalent to the above systems. See also Celestial coordinate ... more details
of the sacrum forward a few degrees vis vis the ilium bone ilia is sometimes called nutation Latin language L. nodding , and the reverse motion counter nutation. ref http www.chiroweb.com archives 14 26 18.html The AS Ilium Fixation, Nutation, and Respect Joseph D. Kurnik, DC Bot generated title ... more details
Explanatory Supplement 1992 , sec. 1.322 and 3.21 ref Main Nutation Once again, this is a simplification ... , and hence the celestial equator, known as nutation . ref cite book author U.S. Naval Observatory ... and nutation are called the true equator and equinox the positions without nutation are the mean equator ... obliquity, that is, without the nutation of the equator included. The true or instantaneous obliquity includes the nutation. ref cite book last Meeus first Jean title Astronomical Algorithms publisher ... the addition of nutation . Eclipses main Eclipse Because the orbit of the Moon is inclined only ... the apparent ecliptic longitude including the effects of Aberration of light aberration and nutation ... more details
to rotate. Flowrate is calculated from the speed of rotation. Nutation Nutating disk A disk ... amount of fluid transferred. Nutating disc flow meters get their name from the idea of nutation , which ... more details
File Polarkreis Finnland 1975.jpg thumb The polar circle in Finland, 1975. File Polarkreis zwischen Narvik & Mo i Rana Norwegen.JPG thumb The polar circle in Norway at Saltfjellet mountain plateau. The year 1940 was added to the inscription by German soldiers during World War II along with a swastika in the centre of the number, later removed . A polar circle is either the Arctic Circle or the Antarctic Circle . On Earth , the Arctic Circle is located at a latitude of Circle of latitude Polar N, and the Antarctic Circle is located at a latitude of Circle of latitude Polar S. ref http www.neoprogrammics.com obliquity of the ecliptic Obliquity of the ecliptic ref Areas between each polar circle and its associated pole North Pole or South Pole , known geographically as the frigid geography frigid zones , would theoretically experience at least one 24 hour period when the sun is continuously above the horizon and at least one 24 hour period when the sun is continuously below the horizon annually. However, due to atmospheric refraction and the Sun being an Angular diameter extended object rather than a point source , the continuous daylight area is somewhat extended while the continuous darkness area is somewhat reduced. br br The exact location of the polar circles differs annually as the rotation axis of the earth shifts due to nutation and precession . Therefore the latitudes noted above are an average of those yearly changes. Clarify reason differs annually is an odd and not very clear form of words. What is an average of yearly changes ? Is it an average over a number of years, an average over one year, or what? And which year s ? date June 2011 class wikitable Image World map with polar circles.svg 300px The polar circles. See also Arctic Circle Antarctic Circle Polar region Arctic Antarctica frigid geography Frigid Zones Polar climate Midnight sun Polar day & Polar night Notes reflist Geographical coordinates state collapsed DEFAULTSORT Polar Circle Ca ... more details
Image Groombridge transit circle.jpg thumb right 150 px Transit circle of Stephen Groombridge Stephen Groombridge Fellow of the Royal Society FRS 7 January 1755, Goudhurst &ndash 30 March 1832, Blackheath, London Blackheath was a British astronomer . In 1806, using a then new Meridian circle transit circle built by Edward Troughton , he began compiling a star catalogue of stars down to about eighth or ninth stellar magnitude magnitude . He spent ten years making observations on the Groombridge Transit Circle and another ten years doing reductions of the data correcting for refraction , instrument error and clock error . In 1827 he suffered a severe attack of paralysis from which he never fully recovered. Others continued the work, continuing with corrections for aberration of light aberration and nutation among others, and his Catalogue of Circumpolar Stars was published posthumously in 1838 with the help of fellow astronomer George Biddell Airy 1801 1892 and others. An earlier edition had been published in 1833 but was found to contain errors and was withdrawn. A few years later in 1842, one of the stars in his catalogue, Groombridge 1830 , was discovered by Friedrich Wilhelm Argelander to have a very high proper motion . For many decades its proper motion was the highest known today it still occupies third place. Selected writings cite book title A Catalogue of Circumpolar Stars author Groombridge, Stephen year 1838 publisher John Murray place London url http www.archive.org details catalogueofcircu00groorich edited by George Biddell Airy has biographical information for Groombridge See also 5657 Groombridge , an asteroid named in his honour Groombridge 1618 , a nearby star Groombridge 34 , a double star. The 16th nearest star system Further reading cite book author Ashbrook, Joseph title The Astronomical Scrapbook year 1984 publisher Sky Publishing location Cambridge, Massachusetts pages 352 &ndash 359 Adapted from Sky & Telescope , May, 1974, page 296 http adsab ... more details
Image DirkvdM natural spiral.jpg thumb A natural left handed helix seen in a tendril of a Vine climber plant. Tendrils often show helix reversals. The term helical growth describes the expansion of fungi fungal , algae algal or higher plant cells or organs leading to a twisted i.e. helical cell biology cell or organ biology organ shape. Helical growth results in the breaking of usually radial symmetry biology . Resulting shapes may be left handed or right handed. Helical growth can arise naturally e.g. as seen in tendrils or in twining plant s ref Goriely, A. and Tabor, M. 1998. Spontaneous helix hand reversal and tendril perversion in climbing plants Phys. Rev. Lett. 80 1564 156 ref or artificially by mutation Arabidopsis thaliana . Helical growth of twining plants is based on a nutation in plants nutational movement of stems circumnutation . When such stems find support this nutational movement may become fixed into a helical winding. Most twining plants show right handed helices regardless of the hemisphere the plant is growing in. ref Edwards, W. et al. 2007. The global trend in plant twining direction. Global Ecol. Biogeogr. 1 6. ref A missense mutation in the conserved grip1 motif, called spiral3, caused a left handed helical organization of cortical microtubule arrays, and severe right handed helical growth. The spiral3 mutation compromises interaction between GCP2 and GCP3, another subunit of the complex, in yeast. In the spiral3 mutant, microtubule dynamics and nucleation efficiency were not markedly affected, but nucleating angles were wider and more divergently distributed. A spiral3 katanin double mutant had swollen and twisted epidermal cells, and showed that the microtubule minus ends were not released from the nucleation sites, although the nucleating angles distributed in a similar manner to those in spiral3. These results show that Arabidopsis GCP2 has an important role in precisely positioning the gamma tubulin containing complex on pre existing mi ... more details
unreferenced date November 2010 Star position in the sky is defined by a pair of angle s. These two angles which refer to the celestial equator are called declination abbrev. or Dec and right ascension or RA . Image AstroDeclinationRightascension.png right The spherical star coordinate system While is given in degree angle degrees kkfrom 90 at the celestial north pole to 90 at the south pole , is usually given in hour s 0 ... 24h . This is due to the observation technique of star transit s, which cross the eyepiece of telescopes because of the Earth s rotation . The observation techniques are topics of position astronomy and of astrogeodesy . Ideally the two dimensional coordinate system , refers to an inertial frame of reference the 3rd coordinate is the star distance which normally is used as an attribute of the individual star. Star positions are changing in time, caused by precession and nutation slow tilts of the Earth s axis with rates of 50 resp. 2 per year Aberration of light aberration and parallax effects of the Earth s orbit around the sun proper motion of the individual stars. The effects 1 and 2 are considered by so called mean places of stars , contrary to their apparent places as seen from the moving Earth. Usually the mean places refer to a special Epoch astronomy epoch , e.g. 1950.0 or 2000.0 . The 3rd effect has to be handled individually. The star positions , are compiled in several star catalogue s of different volume and accuracy. Absolute and very precise coordinates of 1000 3000 stars are collected in Fundamental catalogue s, starting with the FK Berlin 1890 up to the modern FK6 . Relative coordinates of numerous stars are collected in catalogues like the Bonner Durchmusterung Germany 1852 1862, 200.000 rough positions , the Smithsonian Astrophysical Observatory Star Catalog SAO catalogue USA 1966, 250.000 astrometric stars or the Hipparcos and Tycho catalogue 110.000 and 2 million stars by space astrometry . See also Star catalo ... more details
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