Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
7 juillet 2011 4 07 /07 /juillet /2011 10:15

Irregular moons

In order of their distance from the planet, the irregular moons are Triton, Nereid, Halimede, Sao, Laomedeia, Neso and Psamathe, a group that includes both prograde and retrograde objects.[10] The five outer moons are similar to the irregular moons of other giant planets.Compaq PRESARIO R3000 Battery

Triton follows a retrograde and quasi-circular orbit, and is thought to be a gravitationally captured satellite. It is the second known moon in the Solar System to have a substantial atmosphere, which is primarily nitrogen with small amounts of methane and carbon monoxide.[16] The pressure on Triton's surface is about 14 ?bar.HP Compaq Business NX6110 Battery

In 1986 the Voyager 2 spacecraft observed what appeared to be clouds and hazes in this thin atmosphere. Triton is one of the coldest bodies in the Solar System, with a surface temperature of about 38 K (?235.2 °C). Its surface is covered by nitrogen, methane, carbon dioxide and water ices and has a high geometrical albedo of more than 70%.Dell Latitude D610 Adapter

The Bond albedo is even higher, reaching up to 90%.Surface features include the large southern polar cap, older cratered planes cross-cut by graben and scarps, as well as youthful features probably formed by endogenic processes like cryovolcanism.Asus Eee PC 701 Adapter

Voyager 2 observations revealed a number of activegeysers within the polar cap heated by the Sun, which eject plumes to the height of up to 8 km.[4] Triton has a relatively high density of about 2 g/cm3 indicating that rocks constitute about two thirds of its mass, and ices (mainly water ice) the remaining one third. HP Compaq Business NX6325 Battery

There may be a layer of liquid water deep inside Triton, forming a subterranean ocean.

Nereid is the third largest moon of Neptune. It has a prograde but very eccentric orbit and is believed to be a former regular satellite that was shifted to its current orbit through gravitational interactions during Triton's capture.Dell Studio XPS 16 Battery

Water ice has been spectroscopically detected on its surface. Nereid shows irregular large variations of its visible magnitude, which are probably caused by forced precession or chaotic rotation combined with an elongated shape and bright or dark spots on the surface.Acer Aspire 5520 Battery

Among the remaining irregular moons, Sao and Laomedeia follow prograde orbits, while Halimede, Psamathe and Neso follow retrograde orbits. Given the similarity of their orbits, it was suggested that Neso and Psamathe could have a common origin in the break-up of a larger moon.Acer TravelMate 5720 Adapter

Psamathe and Neso have the largest orbits of any natural satellites discovered in the Solar system to date. They take 25 years to orbit Neptune at an average of 125 times the distance between Earth and the Moon. Neptune has the largest Hill sphere in the solar system, owing primarily to its large distance from the Sun; this allows it to retain control of such distant moons.HP Compaq 6735s Adapter


The mass distribution of the Neptunian moons is the most lopsided of any group of satellites in the Solar System. One moon, Triton, makes up nearly all of the mass of the system, with all other moons together comprising only one third of one percent. Dell XPS M1330 Battery

This may be because Triton was captured well after the formation of Neptune's original satellite system, much of which would have been destroyed in the process of capture.

Triton's orbit upon capture would have been highly eccentric, and would have caused chaotic perturbations in the orbits of the original inner Neptunian satellites, causing them to collide and reduce to a disc of rubble.HP Compaq nc6230 Adapter

This means it is likely that Neptune's present inner satellites are not the original bodies that formed with Neptune. Only after Triton's orbit became circularised could some of the rubble re-accrete into the present-day regular moons. It is possible that because of this great perturbation, Dell T117C Battery

the satellite system of Neptune does not follow the 1/10,000 ratio of mass between the parent planet versus all its moons seen in all other gas giants.

The mechanism of Triton’s capture has been the subject of several theories over the years.Asus x5dij-sx039c Battery

One of them postulates that Triton was captured in a three-bodyencounter. In this scenario, Triton is the surviving member of a binary[note 1] disrupted by its encounter with Neptune.

Numerical simulations show that there is a 0.41 probability that the moon Halimede collided with Nereid at some time in the past.Dell Inspiron 1464 Battery

Although it is not known whether any collision has taken place, both moons appear to have similar ("grey") colors, implying that Halimede could be a fragment of Nereid.

The rings of Neptune consist primarily of five principal rings predicted in 1984 by André Brahic and imaged in 1989 by the Voyager 2spacecraft.HP Compaq 6720s Adapter

At their densest, they are comparable to the less-dense portions of Saturn's main rings such as the C ring and the Cassini Division, and much of Neptune's ring system is quite tenuous, faint and dusty, more closely resembling the rings of Jupiter. Neptune's rings are named after astronomers who contributed important work on the planet:Dell Latitude D630 Adapter

Galle, Le Verrier, Lassell, Arago, and Adams. Neptune also has a faint unnamed ring coincident with the orbit of Neptunian moon Galatea. Three other moons orbit between the rings: Naiad, Thalassa andDespina.

The rings of Neptune are made of extremely dark material, likely organic compounds processed by radiation, similar to that found in the rings of Uranus.HP Pavilion dm4 Battery

The proportion of dust in the rings (between 20% and 70%) is high,[4] while their optical depth is low to moderate, at less than 0.1.Uniquely, the Adams ring includes five distinct arcs, named Fraternité, Égalité 1 and 2, Liberté, and Courage. Sony NP-FS11 Battery

The arcs occupy a narrow range of orbital longitudes and are remarkably stable, having changed only slightly since their initial detection in 1980. How the arcs are stabilized is still under debate. However, their stability is probably related to the resonant interaction between the Adams ring and its inner shepherd moon, Galatea.Dell Inspiron 1520 Adapter

Discovery and observations

The first mention of rings around Neptune dates back to 1846 when William Lassell, the discoverer of Neptune's largest moon Triton, thought he had seen a ring around the planet. However, his claim was never confirmed and it is likely that it was an observational artifact. Toshiba PA3399U-1BRS Battery

The first reliable detection of a ring was made in 1968 by stellar occultation, although that result would go unnoticed until 1977 when the rings of Uranus were discovered. Soon after the Uranus discovery, a team from Villanova University led by Harold J. Reitsema began searching for rings around Neptune. Acer Aspire 5920G Adapter

On 24 May 1981, they detected a dip in a star's brightness during one occultation; however, the manner in which the star dimmed did not suggest a ring. Later, after the Voyager fly-by, it was found that the occultation was due to the small Neptunian moonLarissa, a highly unusual event.Acer Aspire 5920 Battery

In the 1980s, significant occultations were much rarer for Neptune than for Uranus, which lay near the Milky Way at the time and was thus moving against a denser field of stars. Neptune's next occultation, on 12 September 1983, resulted in a possible detection of a ring.IBM Thinkpad T40 Adapter

However, ground-based results were inconclusive. Over the next six years, approximately 50 other occultations were observed with only about one-third of them yielding positive results.Something (probably incomplete arcs) definitely existed around Neptune, but the features of the ring system remained a mystery.Nikon COOLPIX 4300 Battery

The Voyager 2 spacecraft made the definitive discovery of the Neptunian rings during its fly-by of Neptune in 1989. It confirmed that occasional occultation events observed before were indeed caused by the arcs within the Adams ring (see below).Apple MB771 Battery

After the Voyager fly-by the previous terrestrial occultation observations were reanalyzed yielding features of the ring's arcs as they were in 1980s, which matched those found by Voyager almost perfectly.

Since Voyager's fly-by, the brightest rings (Adams and Le Verrier) have been imaged with the Hubble Space Telescope and Earth-based telescopes, owing to advances in resolution and light-gathering power.Sony DSC-P5 Battery

They are visible, slightly above background noise levels, at methane-absorbing wavelengths in which the glare from Neptune is significantly reduced. The fainter rings are still far below the visibility threshold.Dell Inspiron 6400 Adapter

General properties

Neptune possesses five distinct rings named, in order of increasing distance from the planet, Galle, Le Verrier, Lassell, Arago and Adams. In addition to these well-defined rings, Neptune may also possess an extremely faint sheet of material stretching inward from the Le Verrier to the Galle ring, and possibly farther in toward the planet.Toshiba PA3534U-1BRS Battery

Three of the Neptunian rings are narrow, with widths of about 100 km or less; in contrast, the Galle and Lassell rings are broad—their widths are between 2,000 and 5,000 km.[4] The Adams ring consists of five bright arcs embedded in a fainter continuous ring.Sony NP-FP50 Battery

Proceeding counterclockwise, the arcs are: Fraternité, Égalité 1 and 2, Liberté, and Courage. The first three names mean liberty, equality, and fraternity, after the famous motto of the French Revolution. The terminology was suggested by their original discoverers, who had found them during stellar occultations in 1984 and 1985.HP Compaq nx7300 Adapter

Four small Neptunian moons have orbits inside the ring system: Naiad and Thalassa orbit in the gap between the Galle and Le Verrier rings; Despina is just inward of the Le Verrier ring; and Galatea lies slightly inward of the Adams ring,[3] embedded in an unnamed faint, narrow ringlet.Dell Latitude D820 Adapter

The Neptunian rings contain a large quantity of micrometer-sized dust: the dust fraction by cross-section area is between 20% and 70%.[6] In this respect they are similar to the rings of Jupiter, in which the dust fraction is 50%–100%, and are very different from the rings of Saturn and Uranus, which contain little dust (less than 0.1%).Toshiba PA3399U-1BRS Battery

The particles in Neptune's rings are made from a dark material; probably a mixture of ice with radiation-processed organics. The rings are reddish in color, and their geometrical (0.05) and Bond (0.01–0.02) albedos are similar to those of the Uranian rings' particles and the inner Neptunian moons.Dell Studio XPS 1640 Battery

The rings are generally optically thin (transparent); their normal optical depths do not exceed 0.1.[4] As a whole, the Neptunian rings resemble those of Jupiter; both systems consist of faint, narrow, dusty ringlets and even fainter broad dusty rings.[Dell Latitude D830 Battery

The rings of Neptune, like those of Uranus, are thought to be relatively young; their age is probably significantly less than that of the Solar System.[4] Also, like those of Uranus, Neptune's rings likely resulted from the collisional fragmentation of onetime inner moons.Dell Inspiron E1505 Adapter

Such events create moonlet belts, which act as the sources of dust for the rings. In this respect the rings of Neptune are similar to faint dusty bands observed by Voyager 2 between the main rings of Uranus.

Inner rings

The innermost ring of Neptune is called the Galle ring after Johann Gottfried Galle, the first person to see Neptune through a telescope (1846).Asus Eee PC 1201PN Battery

It is about 2,000 km wide and orbits 41,000–43,000 km from the planet. It is a faint ring with an average normal optical depth of around 10?4, and with an equivalent depth of 0.15 km. The fraction of dust in this ring is estimated from 40% to 70%.

The next ring is named the Le Verrier ring after Urbain Le Verrier, who predicted Neptune's position in 1846.Asus Eee PC 701 Adapter

With an orbital radius of about 53,200 km, it is narrow, with a width of about 113 km.[5]Its normal optical depth is 0.0062 ± 0.0015, which corresponds to an equivalent depth of 0.7 ± 0.2 km.[5] The dust fraction in the Le Verrier ring ranges from 40% to 70%.Dell XPS M1330 Battery

The small Neptunian moon Despina, which orbits just inside of it at 52,526 km, may play a role in the ring's confinement by acting as a shepherd.

The Lassell ring, also known as the plateau, is the broadest ring in the Neptunian system.fujifilm np95 Battery

It is the namesake of William Lassell, the English astronomer who discovered Neptune's largest moon,Triton. This ring is a faint sheet of material occupying the space between the Le Verrier ring at about 53,200 km and the Arago ring at 57,200 km.[3] Its average normal optical depth is around 10?4, which corresponds to an equivalent depth of 0.4 km.Asus Eee PC 900 Adapter

The ring's dust fraction is in the range from 20% to 40%.

There is a small peak of brightness near the outer edge of the Lassell ring, located at 57,200 km from Neptune and less than 100 km wide,[3] which some planetary scientists call the Arago ring afterFrançois Arago, a French mathematician, physicist, astronomer and politician.[16] However, many publications do not mention the Arago ring at all.Sony VAIO PCG-713 Battery

Adams ring

The outer Adams ring, with an orbital radius of about 63,930 km,[3] is the best studied of Neptune's rings.[3] It is named after John Couch Adams, who predicted the position of Neptune independently of Le Verrier.Dell Latitude D830 Adapter

This ring is narrow, slightly eccentric and inclined, with total width of about 35 km (15–50 km), and its normal optical depth is around 0.011 ± 0.003 outside the arcs, which corresponds to the equivalent depth of about 0.4 km.[5] The fraction of dust in this ring is from 20% to 40%—lower than in other narrow rings.Dell Studio XPS 1640 Battery

Neptune's small moon Galatea, which orbits just inside of the Adams ring at 61,953 km, acts like a shepherd, keeping ring particles inside a narrow range of orbital radii through a 42:43 outerLindblad resonance.[11] Galatea's gravitational influence creates 42 radial wiggles in the Adams ring with an amplitude of about 30 km, which have been used to infer Galatea's mass.Panasonic LUMIX DMC-TZ4S  Battery


The brightest parts of the Adams ring, the ring arcs, were the first elements of Neptune's ring system to be discovered.The arcs are discrete regions within the ring in which the particles that comprise it are mysteriously clustered together. The Adams ring is known to comprise five short arcs, which occupy a relatively narrow range of longitudes from 247° to 294°.HP Compaq Business NX6320 Battery

In 1986 they were located between longitudes of:

  • 247–257° (Fraternité),
  • 261–264° (Égalité 1),
  • 265–266° (Égalité 2),  Canon POWERSHOT G2 Battery
  • 276–280° (Liberté),
  • 284.5–285.5° (Courage).

The brightest and longest arc was Fraternité; the faintest was Courage. The normal optical depths of the arcs are estimated to lie in the range 0.03–0.09 (0.034 ± 0.005 for the leading edge of Liberté arc as measured by stellar occultation);[5] the radial widths are approximately the same as those of the continuous ring—about 30 km.Dell Latitude E6500 Battery

The equivalent depths of arcs vary in the range 1.25–2.15 km (0.77 ± 0.13 km for the leading edge of Liberté arc).[5] The fraction of dust in the arcs is from 40% to 70%.[13] The arcs in the Adams ring are somewhat similar to the arc in Saturn's G ring.Dell LATITUDE D630 Battery

The highest resolution Voyager 2 images revealed a pronounced clumpiness in the arcs, with a typical separation between visible clumps of 0.1° to 0.2°, which corresponds to 100–200 km along the ring. Because the clumps were not resolved, they may or may not include larger bodies,Asus R33030 Adapter

but are certainly associated with concentrations of microscopic dust as evidenced by their enhanced brightness when backlit by the Sun.

The arcs are quite stable structures. They were detected by ground based stellar occultations in the 1980s, Dell Mini 1011 Battery

by Voyager 2 in 1989 and by Hubble Space Telescope and ground based telescopes in 1997–2005 and remained at approximately the same orbital longitudes.However some changes have been noticed. The overall brightness of arcs decreased since 1986.Acer Aspire 5052ANWXMi Battery

The Courage arc jumped forward by 8° to 294° (it probably jumped over to the next stable co-rotation resonance position) while the Liberté arc had almost disappeared by 2003.[19] The Fraternité and Égalité (1 and 2) arcs have demonstrated irregular variations in their relative brightness. Dell Mini 1011v Battery

Their observed dynamics is probably related to the exchange of dust between them. Courage, a very faint arc found during the Voyager flyby, was seen to flare in brightness in 1998, while more recently it was back to its usual dimness. HP Compaq nx7300 Adapter

Visible light observations show that the total amount of material in the arcs has remained approximately constant, but they are dimmer in the infrared light wavelengths where previous observations were taken.


The arcs in the Adams ring remain unexplained.Dell Vostro 1510 Battery

Their existence is a puzzle because basic orbital dynamics imply that they should spread out into a uniform ring over a matter of years. Several theories about the arcs' confinement have been suggested, the most widely publicized of which holds that Galatea confines the arcs via its 42:43 co-rotational inclination resonance (CIR).Toshiba PA3534U-1BRS Battery

The resonance creates 84 stable sites along the ring's orbit, each 4° long, with arcs residing in the adjacent sites. However measurements of the rings' mean motion with Hubble and Keck telescopes in 1998 led to the conclusion that the rings are not in CIR with Galatea.Asus M50 Battery

A later model suggested that confinement resulted from a co-rotational eccentricity resonance (CER).The model takes into account the finite mass of the Adams ring, which is necessary to move the resonance closer to the ring. A byproduct of this theory is a mass estimate for the Adams ring—about 0.002 of the mass of Galatea.Asus Eee PC 901 Battery

A third theory proposed in 1986 requires an additional moon orbiting inside the ring; the arcs in this case are trapped in its stable Lagrangian points. However Voyager 2's observations placed strict constraints on the size and mass of any undiscovered moons, making such a theory unlikely.Dell Inspiron 6400 Battery

Some other more complicated theories hold that a number of moonlets are trapped in co-rotational resonances with Galatea, providing confinement of the arcs and simultaneously serving as sources of the dust.HP Compaq Business NC6220 Battery


The rings were investigated in detail during the Voyager 2 spacecraft's flyby of Neptune in August 1989.[4] They were studied with optical imaging, and through observations of occultations in ultraviolet and visible light.Sony VGP-BPS9 Battery

Voyager 2 observed the rings in different geometries relative to the Sun, producing images of back-scattered, forward-scattered and side-scattered light.[g][4] Analysis of these images allowed derivation of the phase function (dependence of the ring's reflectivity on the angle between the observer and Sun), and geometrical and Bond albedo of ring particles.Sony VGP-BPS13 Battery

Analysis of Voyager's images also led to discovery of six inner moons of Neptune, including the Adams ring shepherd Galatea.

Neptune was mathematically predicted before it was directly observed.HP Compaq nx7300 Adapter

With a prediction by Urbain Le Verrier, telescopic observations confirming the existence of a major planet were made on the night of September 23, 1846, and into the early morning of the 24th, at the Berlin Observatory, by astronomer Johann Gottfried Galle (assisted by Heinrich Louis d'Arrest), working from Le Verrier's calculations. HP Compaq 2510p Adapter

It was a sensational moment of 19th century science and dramatic confirmation of Newtonian gravitational theory. In François Arago's apt phrase, Le Verrier had discovered a planet "with the point of his pen."

In retrospect, after it was discovered it turned out it had been observed many times before, Dell Studio PP39L Battery

but not recognized, and there were others who made various calculations about its location, but did not lead to its observation. By 1846, the planet Uranus had completed nearly one full orbit since its discovery byWilliam Herschel in 1781, and astronomers had detected a series of irregularities in its path which could not be entirely explained by Newton's law of gravitation.Nikon COOLPIX 5700  Battery

These irregularities could, however, be resolved if the gravity of a farther, unknown planet were disturbing its path around the Sun. In 1845, astronomers Urbain Le Verrier in Paris and John Couch Adams in Cambridge separately began calculations to determine the nature and position of such a planet. Dell Studio XPS 16 Battery

Unfortunately, Le Verrier's triumph also led to a tense international dispute over priority, as, shortly after the discovery, George Airy, at the time British Astronomer Royal, announced that Adams had also predicted the discovery of the planet. Nevertheless, the Royal Society awarded Le Verrierthe Copley medal in 1846 for his achievement, without mention of Adams.HP Compaq nx7400 Adapter

The discovery of Neptune led to the discovery of its moon Triton by William Lassell just seventeen days later.

Earlier observations

Neptune is invisible to the naked eye as it is too dim (apparent magnitude is never less than 7.7 ) and too small (peak angular size is 2.4 arcseconds ). HP Pavilion DV6500 Adapter

Therefore, the first observations of Neptune were only possible after the invention of the telescope. There is evidence that Neptune was seen and recorded by Galileo Galilei in 1613, Jérôme Lalande in 1795 and John Herschel in 1830, but none is known to have recognized it as a planet at the time.Dell T117C Battery

These pre-discovery observations were important in accurately determining the orbit of Neptune. Neptune would appear prominently even in early telescopes so other pre-discovery observation records are likely.

Galileo's drawings show that he observed Neptune on December 28, 1612, and again on January 27, 1613;Acer PA-1650-02 Adapter

on both occasions, Galileo mistook Neptune for a fixed star when it appeared very close (inconjunction) to Jupiter in the night sky.[9] Historically it was thought that he believed it to be a fixed blue star, and so he is not credited with its discovery. Acer Aspire 5920G Adapter

At the time of his first observation in December 1612, it was stationary in the sky because it had just turned retrograde that very day; because it was only beginning its yearly retrograde cycle, Neptune's motion was thought to be too slight, and its apparent size too small, to clearly appear to be a planet in Galileo's small telescope.Asus S1 Adapter

However, in July 2009 University of Melbourne physicist David Jamieson announced new evidence suggesting that Galileo was indeed aware that he had discovered something unusual about this star. Galileo, in one of his notebooks, noted the movement of a background star (Neptune) on January 28 and a dot (in Neptune's position)HP Pavilion dv6000 Battery

drawn in a different ink suggests that he found it on an earlier sketch, drawn on the night of January 6, suggesting a systematic search among his earlier observations. However, so far there is neither clear evidence that he identified this moving object as a planet, nor that he published these observations of it. There is no evidence that he ever attempted to observe it again.Ibm Thinkpad T30 Battery

In 1847, Sears C. Walker of the U.S. Naval Observatory searched historical records and surveys for possible prediscovery sightings of the planet Neptune. He found that observations made by Lalande'sstaff at the Paris Observatory in 1795 were in the direction of Neptune's position in the sky. Dell Studio PP39L Battery

In the catalog observations for May 8 and again on May 10 of 1795 a star was observed in the approximate position expected for Neptune. The uncertainty of the position was noted with a colon. HP Pavilion dv5 Adapter

This notation was also used to indicate an observation error so it was not until the original records of the observatory were reviewed that it was established with certainty that the object was Neptune and the position error in the observations made two nights apart was due to the planet's motion across the sky.HP Compaq Business NC6400 Battery

The discovery of these records of Neptune's position in 1795 led to a better calculation of the planet's orbit.

John Herschel almost discovered Neptune the same way his father, William Herschel, had discovered Uranus in 1781, by chance observation. HP Compaq 490306-001 Battery

In an 1846 letter to Wilhelm Struve, John Herschel states that he observed Neptune during a sweep of the sky on July 14, 1830. Although his telescope was powerful enough to resolve Neptune into a small blue disk and show it to be a planet, he did not recognize it at the time and mistook it for a star. Compaq Presario CQ35-100 Battery

Irregularities in Uranus's orbit

In 1781, Anders Johan Lexell was the first to compute the orbit of Uranus and notice that it had irregularities. He suggested that there might be other planets in Solar system that perturb the orbit ofUranus, with the Solar system ranging as far as 100 A. U.HP Compaq HSTNN-LB51 Battery

In 1821, Alexis Bouvard had published astronomical tables of the orbit of Uranus, making predictions of future positions based on Newton's laws of motion and gravitation. Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize some perturbing body.HP Pavilion ZE4500 Battery

These irregularities or "residuals", both in the planet's ecliptic longitude and in its distance from the Sun, or radius vector, might be explained by a number of hypotheses: the effect of the Sun's gravity, at such a great distance, might differ from Newton's description;HP G62-100EB Battery

or the discrepancies might simply be observational error; or perhaps Uranus was being pulled, or perturbed, by an as-yet undiscovered eighth planet.

Adams learned of the irregularities while still an undergraduate and became convinced of the "perturbation" hypothesis. HP Pavilion DV6-1211AX Battery

Adams believed, in the face of anything that had been attempted before, that he could use the observed data on Uranus, and utilising nothing more than Newton's law of gravitation, deduce the mass, position and orbit of the perturbing body.

After his final examinations in 1843, Adams was elected fellow of his college and spent the summer vacation in Cornwall calculating the first of six iterations.HP Pavilion DV6-1220SO Battery

In modern terms, the problem is an inverse problem, an attempt to deduce the parameters of a mathematical model from observed data. Though the problem is a simple one for modern mathematics after the advent ofelectronic computers, at the time it involved much laborious hand calculation. HP EliteBook 6930P Battery

Adams began by assuming a nominal position for the hypothesised body, using the empirical Bode's law. He then calculated the path of Uranus using the assumed position of the perturbing body and calculated the difference between his calculated path and the observations, in modern terms the residuals.HP Pavilion DV6-1210SA Battery

He then adjusted the characteristics of the perturbing body in a way suggested by the residuals and repeated the process, a process similar to regression analysis.

On 13 February 1844, James Challis, director of the Cambridge Observatory, requested data on the position of Uranus, Compaq Presario CQ71 Battery

for Adams, from Astronomer Royal George Biddell Airy at the Royal Observatory, Greenwich.[1] Adams certainly completed some calculations on 18 September 1845.

Supposedly, Adams communicated his work to Challis in mid-September 1845 but there is some controversy as to how. HP Pavilion DV7-1290EO Battery

The story and date of this communication only seem to have come to light in a letter from Challis to the Athenaeum dated 17 October 1846. However, no document was identified until 1904 when Sampson suggested a note in Adams's papers that describes "the New Planet" and is endorsed, in handwriting not Adams's, with the note "Received in September 1845".HP G6000 Battery

Though this has often been taken to establish Adams's priority, some historians have disputed its authenticity, on the basis that "the New Planet" was not a term current in 1845, and on the basis that the note is dated only after the fact by someone other than Adams.HP HDX X18-1005EA Battery

Further, the results of the calculations are different from those communicated to Airy a few weeks later. Adams certainly gave Challis no detailed calculations and Challis was unimpressed by the description of his method of successively approximating the position of the body,HP Pavilion DV6-3013SL Battery

being disinclined to start a laborious observational programme at the observatory, remarking "while the labour was certain, success appeared to be so uncertain."

Meanwhile, Urbain Le Verrier, on November 10, 1845, presented to the Académie des sciences in Paris a memoir on Uranus, showing that the pre-existing theory failed to account for its motion.HP Compaq HSTNN-IB62 Battery

Unaware of Adams's work, he attempted a similar investigation, and on June 1, 1846, in a second memoir presented to a public meeting of the Académie, gave the position, but not the mass or orbit, of the proposed perturbing body. Le Verrier located Neptune within one degree of its predicted position.HP Pavilion DV6100 Battery

The search

Upon receiving in England the news of Le Verrier's June prediction, George Airy immediately recognized the similarity of Le Verrier's and Adams' solutions. Up until that moment, Adams' work had been little more than a curiosity, but independent confirmation from Le Verrier spurred Airy to organize a secret attempt to find the planet.HP EliteBook 2730P Battery

At a July 1846 meeting of the Board of Visitors of the Greenwich Observatory, with Challis and Sir John Herschel present, Airy suggested that Challis urgently look for the planet with the Cambridge 11.25 inch equatorial telescope, "in the hope of rescuing the matter from a state which is ... almost desperate".HP Pavilion DV9000 Battery

The search was begun by a laborious method on 29 July. Adams continued to work on the problem, providing the British team with six solutions in 1845 and 1846 which sent Challis searching the wrong part of the sky. HP Pavilion DV7 Battery

Only after the discovery of Neptune had been announced in Paris and Berlin did it become apparent that Neptune had been observed on August the 8th and August the 12th but because Challis lacked an up-to-date star-map, it was not recognized as a planet. HP Pavilion DV7-1290EO Battery

Discovery Observation: September 24th 1846

Le Verrier was unaware that his public confirmation of Adams' private computations had set in motion a British search for the purported planet. On 31 August, Le Verrier presented a third memoir, now giving the mass and orbit of the new body.HP Compaq Business 6735S Battery

Having been unsuccessful in his efforts to interest any French astronomer in the problem, Le Verrier finally sent his results by post to Johann Gottfried Galleat the Berlin Observatory. Galle received Le Verrier's letter on 23 September and immediately set to work observing in the region suggested by Le Verrier.HP 540 Battery

Galle's student, Heinrich Louis d'Arrest, suggested that a recently drawn chart of the sky, in the region of Le Verrier's predicted location, could be compared with the current sky to seek the displacement characteristic of a planet, as opposed to a stationary star.HP Compaq Business NW9440 Battery

Neptune was discovered just after midnight,  after less than an hour of searching and less than 1 degree from the position Le Verrier had predicted, a remarkable match. After two further nights of observations in which its position and movement were verified, Galle replied to Le Verrier with astonishment: HP Compaq Business  TC4400 Battery

"the planet whose place you have [computed] really exists" (emphasis in original). The discovery telescope was an equatorial mounted achromatic refractor by Joseph Fraunhofer's firm Merz und Mahler.


On the announcement of the discovery, Herschel, Challis and Richard Sheepshanks, foreign secretary of the Royal Astronomical Society, HP Compaq 491278-001 Battery

announced that Adams had already calculated the planet's characteristics and position. Airy, at length, published an account of the circumstances, and Adams's memoir was printed as an appendix to the Nautical Almanac. However, it appears that the version published by HP HSTNN-LB31 Battery

Airy had been edited by the omission of a "crucial phrase" to disguise the fact that Adams had quoted only mean longitude and not the orbital elements.

A keen controversy arose in France and England as to the merits of the two astronomers. HP Pavilion DV3-4000  Battery

There was much criticism of Airy in England. Adams was a diffident young man who was naturally reluctant to publish a result that would establish or ruin his career. Airy and Challis were criticised, particularly by James Glaisher, as failing to exercise their proper role as mentors of a young talent. HP Pavilion TX1000 Battery

Challis was contrite but Airy defended his own behaviour, claiming that the search for a planet was not the role of the Greenwich Observatory. On the whole, Airy has been defended by his biographers. In France the claims made for an unknown Englishman were resented as detracting from the credit due to Le Verrier's achievement.HP Pavilion DV6-1210SA  Battery

The Royal Society awarded Le Verrier the Copley medal in 1846 for his achievement, without mention of Adams, but Adams's academic reputation at Cambridge, and in society, was assured. As the facts became known, some British astronomers pushed the view that the two astronomers had independently solved the problem of Uranus, and ascribed equal importance to each.HP 448007-001 Battery

But Adams himself publicly acknowledged Le Verrier's priority and credit (not forgetting to mention the role of Galle) in the paper that he gave to the Royal Astronomical Society in November 1846:HP Compaq Business  6530B  Battery

I mention these dates merely to show that my results were arrived at independently, and previously to the publication of those of M. Le Verrier, and not with the intention of interfering with his just claims to the honours of the discovery ;HP Pavilion DV5-1015EA  Battery

for there is no doubt that his researches were first published to the world, and led to the actual discovery of the planet by Dr. Galle, so that the facts stated above cannot detract, in the slightest degree, from the credit due to M. Le Verrier.HP Pavilion DV6-1230SB Battery

The criticism was soon afterwards made, that both Adams and Le Verrier had been over-optimistic in the precision they claimed for their calculations, and both had greatly overestimated the planet's distance from the sun. Further, it was suggested that they both succeeded in getting the longitude almost right only because of a "fluke of orbital timing". HP Pavilion ZD8181EA  Battery

This criticism was discussed in detail by Danjon (1946)   who illustrated with a diagram and discussion that while hypothetical orbits calculated by both LeVerrier and Adams for the new planet were indeed of very different size on the whole from that of the real Neptune (and actually similar to each other),HP Pavilion DV9500  Battery

they were both much closer to the real Neptune over that crucial segment of orbit covering the interval of years for which the observations and calculations were made, than they were for the rest of the calculated orbits. So the fact that both the calculators used a much larger orbital major axis than the reality was shown to be not so important, and not the most relevant parameter.HP Pavilion DV4-1125BR  Battery

The new planet, at first called "Le Verrier" by Francois Arago, received by consensus the neutral name of Neptune. Its mathematical prediction was a great intellectual feat, but it showed also that Newton's law of gravitation, which Airy had almost called in question, prevailed even at the limits of the solar system.HP Pavilion DV5-1111EA Battery

Adams held no bitterness towards Challis or Airy  and acknowledged his own failure to convince the astronomical world:

I could not expect however that practical astronomers, who were already fully occupied with important labours, would feel as much confidence in the results of my investigations, as I myself did.HP Pavilion DV6-1234TX Battery

By contrast, Le Verrier was arrogant and assertive, enabling the British scientific establishment to close ranks behind Adams while the French, in general, found little sympathy with Le Verrier. In 1874–1876, Adams was president of the Royal Astronomical Society when it fell to him to present the gold medal of the year to Le Verrier.HP Pavilion DV3-2008TX  Battery

Later analysis

The conventional wisdom that Neptune's discovery should be "credited to both Adams and Le Verrier" has recently been challenged putting in doubt the accounts of Airy, Challis and Adams in 1846.HP Pavilion DV8  Battery

In 1999, Adams's correspondence with Airy, which had been lost by the Royal Greenwich Observatory, was rediscovered in Chile among the possessions of astronomer Olin J. Eggen after his death. In an interview in 2003, historian Nicholas Kollerstrom concluded that Adams's claim to Neptune was far weaker than had been suggested, HP Pavilion DV6-1215SA  Battery

as he had vacillated repeatedly over the planet's exact location, with estimates ranging across 20 degrees of arc. Airy's role as the hidebound superior willfully ignoring the upstart young intellect was, according to Kollerstrom, largely constructed after the planet was found, in order to boost Adams's, and therefore Britain's, credit for the discovery.HP Compaq 490306-001  Battery

A later Scientific American article by Sheehan, Kollerstrom and Waff claimed more boldly "The Brits Stole Neptune" and concluded "The achievement was Le Verrier's alone."

Neptune Discovery Telescope

The telescope at New Berlin Observatory (1835–1913), that discovered Neptune, was an achromatic refractor of 9 Paris inch (9.6 English inches or 24.4 cm)Compaq Presario CQ50  Battery

aperture made by the late Joseph Fraunhofer's firm, Merz und Mahler. It was a high performance telescope of its era, with one of the largest achromatic doublets available and a finely made equatorial mount, with a clockwork drive to move the 4 m (13.4?) main tube in time with Earth's rotation.HP Pavilion DV6-1223EO  Battery

Eventually the telescope was moved to Deutsches Museum in München, Germany, where it can still be seen in the 21st century as an exhibit.-490306-001-battery-33764.htm">HP Compaq 490306-001  Battery,HP Pavilion DM4 Battery,Dell Latitude E6400 Battery,HP Pavilion DV6-1020ED Battery,HP Pavilion DV7-1290EO Battery

Partager cet article

Repost 0
Published by batterys - dans Laptop Battery
commenter cet article