User:Serendipodous/indigo/page 10
burgess, 1988[edit]
As Voyager approached Miranda, it showed only intensely varied albedo features
Jan 25 1986 When the Voyager team saw the first close up images of Miranda, they gasped.
chevrons- bright and dark linear faults
displacement of blocks at the surface
gigantic bite
cratered grooved and jumbled
taken apart and put back together
craters- rolling hills, subdued craters of medium size
grooves from when terrain shifted downward
could the catastrophic event that turned Uranus on its side also have splashed the moons, or is their darkness the result of sunlight convertingmethane ice on their surfaces to complex organic polymers
Volcanic flows?
there are no large impact craters on miranda
the satellites of Uranus are much rockier than the satellites of Saturn, to the point where heat from radioactive decay may have led to internal differentiation.
Uranus's magnetic field is comparable in strength to, though larger than, Earth's
All the major satellites inhabit the magnetosphere, and thus sweep their zones free of plasma
satellites as small as 15 km should have been seen
geologic activity has reworked their surfaces, obliterating traces of the earlier impact events
magnetosphere particles split methane into carbon and hydrogen
faults on miranda are similar to those on Mercury
Elkins tanton 2006[edit]
Miranda's surface is old, and yet covered in strange features
coronae formed after the cratering period
Arden is surrounded by a deep canyon
canyons 100s km long and 10s km wide formed pss. by stretching of the surface by expanding underside
Miranda is too small for any significant heat from accretion to have been retained
water and ammonia or methanol would have flowed more visciously and frozen like rock
Miranda coronae geologically active- volcanic or tectonic
canyons formed from the rising of internal material and cracking of the crust
How miranda, which is too small to have any geological activity, could have evidence of upwelling is still not known
water, ammonia and methanol may be viscous enough to mimic lava
Miner, 1990[edit]
the larger satellites are large enough to be differentiated, for brighter water ice to rise to the surface, likely leading to their brighter albedos
The moons of Uranus are of comprable size to the mid-range moons of Staturn, though more geologically active
facing the sun, max temp 85 k yet water flows. fossil from past, more recent localised heating, or a mixture of water and ammonia?
resurfacing before the LHB ended, cracks probably due to ice expansion
309-319
Miranda secodn brightest albedo 32%
most eccentric
Elsinore corona has no surrounding trench and an albedo similar albedo to the surrouncding region
The perss were shown images of Miranda just 24 hours after they were taken. Too little time for any conclusions to be drawn
They had expected Miranda to be like Mimas
ancient cratered terrain indicates early history was similar to other Uranian satellites
crater rims are softened, either by ejecta or cryovolcanism
coronae and fractures postdate the early bombardment and that tehy are related
scars from bombardment were covered by recent surface materials
Soderblom: partial differentiation, heavier materials sank to the bottom and lighter (watery) materials rose. freezing and expansion fractured the surface
- 2 surface heating by tidal forces during amore eccentirc early period
Arden was originaly an impact basin, hence the concentric features around it
inverness corona formed in two massive cryovolcanic events; the first extruded dark material (like Arden) the secon had less carbonaceous material and formed the chevron seen in Inverness
the third hypothesis is that Miranda was shattered by an impact and reassembled into a random jumble. Three rock impacts created the coronae, the unbalanced mass distribnution caused Miranda to rotate so that Arden or Elsinore was pointed toweards uranus.
Then as the subsurface melted, ice rose to fill the void as the heavier material fell down
This caused miranda to reorient itself so that Arden was the Uranus facing hemisphere and elsinor was whte trailing hemisphere
the coronae could have formed form upwellings during earlier resonance periods
Miner et al 1991[edit]
James Pollack and Jonathan Lunine Satellite Origin Uranus Uni Ariz Press 1991 pp. 469-512
RH Brown et al physical properties of the Uranuian satellites pp 513-528
due to the moons pole on rotation, determining their masses from their effects on Voyager 2 was not as simple. and requiired combining info from navigation data and ground based measurements
miranda and ariel are the least spherical of the moons
bulgy, like mimas
if umbriel's peak is an impact basin, it would be the largest in the Uranian system
5% of miranda's radius
sufficiently fluid to form into a sphere, but crust has been cold and rgid not as affected by viscous relaxation
the unramian satellites are too small for their constituents to undergo significant compression
Miranda resembles the small saturnian satellites and is signficantly lower density than the other uranians
explanations for this high density have included that the co and ch4 in the nebula condensed into carbon-rich material or even graphite.
However, this is unlikely as graphite is unlikely to form in such a nebula
Uranus satellites surface protperties Veverka J Hamilton Brown R Bell Jeffrey F 528-560
miranda and ariel s pole max 87 k 86 k
20 to 30 k night time (40 years in total darkness)
methane ammionia nitrogen frozen out 2.5 m diurnal skin depth, spring would see them begin to outgas
solid state greenhouse effect
dark material on all satellites similar to asteroid f material
magnetosphere alteration of methane
endogenic origin
methane has not been identified on any uranian satellite
A popular hypothesis is that megnetospheric particles stripped methane or clathrate of its hydrogen, leaving pure carbon
geology of the uranian satellites croft soderblom pp. 561 to 628
USGS map Oberon low res only
oberon cratering ismilar to lunar highlands
grabens or contienttnal rifts and are thus interpreted as extensional topographic features
lack of an obvious crater rim (size of anaeas peak on Dione
flat plain 500 km across
Evidence for cryomagmatic flooding on oberon is controversial, with some arguing that Oberon is inert, and others arguing lower crater counts
passive extensional failure in the brittle lithosphere
titania: no 100+ km craters- these exist on other moons and so must have been covered by global volcanic resurfacing at least km thick
umbriel crater size distribution identical to oberon
extrusive cryovolcanic origin vuver spot
because all the grabens run in a general direction, they are generally seen to be part of a single event. they cut through young craters, indicating a post LHB
the origin of umbriel's uniform darkness is unclear; is it external, like cryovolcanism, external, such as an impact or a coating from a dark ring, or simply evidence that Umbriel never evolved?
bright spot on wunda indicates differentiation, so cryovolcanims is usually seen as the most likely hypothesis
It would have to be 10s of km thick and ancient to account for the dark craters
Much like Venus and Earth, Ariel and Umbriel are adjacent twins with polar opposite identities
Ariel is bright and shows multiple examples of tectonic resurfacing
least cratered cratered region
cratering suggests that earlier cratering events were covered over by volcanic resurfacing
massive impact or global-scale eruption
faulting active throughout ariel's history
this water would have the viscosity of lava
1% global expansion create faults
Astronomers expected Miranda to resemble Mimas; an inert lump covered in craters
miranda cratered terrain uniform albedo and texture
similar to the lunar highlands
of all the moons, Miranda was the most covered
craters on miranda re either very old and eroded or fresh with sharp rims
coronae darker and lighter units, crisp frresh texture and low crater density
Inverness materials like in a depression defined by mantled scarps in the north west and south
the corona is lower in altitude than the surrounding terrain, thoughdomes and ridges are of comprable elevation
eastern bound by ridge of 340 degree chasma
the ridge is overlain by coronal material at its southern and northern ends
chevron, comprised of ripples paralleling the unit's edges
Elsinore stands higher than the terrain
Arden has an albedo in line with the cratered terrain
ripple texture is not seen
inverness part of the canyon system; arden an old degraded impact basin
radial crater chains and fracture, radial ejecta
original crater 300 km wide and 10 km deep
coronae: extrusive volcanic deposits?
two global sets of fractures approximately orthogonal
multiple fresh and mantled scarp bout the ne side of the 340 chasma indicating mutiple failture events along the same fault line
canyons are all 35 +- 5 km wide and 6 to 8 km deep bounded by inward facing scarps
mantled and fresh craters indicate a single 1 km deep mantling event over entire surface
the mantling event is believed to have been formed by the same impact that formed arden
Fresh craters suggest that Arden and Inverness deposits forfmed roughly contepmeraneously shortly after the mantling event
340 degree and arden concentric chasmata are contiunuous, thus formed at around the same time, but
they cut arden deposits and are overlain by inverness deposits
if catastrophic disruption occurred (smith et al say yes, lissuar sayse no) then it must have been early enough to produce a uniform crater density
the earliest chasmata form, then the arden impact wipes out all carters smaller than 3-5 km wide
deposits of ejecta splashed against scarps
some material was sent into orbit, coming down and softening the contours of the craters
2 x 10^5 km ^3 material flooded arden basin
magmatic uplift of arden's floor may have occurred concurrently
cracks and concentric rifts formed around Arden
3 x 10^4 km^3 material erupted for Inverness Corona
10^5 km^3 for Elsinore
not surface dusting by dark meteorites there is no correlation of albedo with age the youngest features (the Mirandan coronae) also feature the strongest albedo differences
Morphologies of the canyons are quite smiliar on all moosns
characteristics of grabesn or simple faults or terrestrial contienntal rifts
R Greenberg, SK Croft et al University of Arizona Miranda pp. 693-735
4.2 degree inclination was surprising
coronae 200-300 km across
nothing except water has been detected though (+-3%) ch4, co, N nh3 may also exist
most old, heavily cratered terrain
definitely some volcanism, possibly lots
all coronae have squarish interior regions surrounded by banded concentric lines
less cratered than the surrounding terrain
abrupt, clearly defined edges
rock mass fraction of 0.2-0.4, much less than the other moons
waer-ammonia melts at 176 k, lower than pure water, making melting a possibility on a world as small as Miranda
The Uranian subnebula could have contained ammonia, but if it was spun out by a giant impact, most of the nitrogen would be in the form of N2
too viscous to be pure liquid water, too fluid to be pure solid water
the second, younger impact population apepars to be a few times greater on the leading hemisphere than on the trailing one
Miranda is too small for radeogenic heating to produce melting
3:1 resonance with umbriel could have produced a 20 k increase in temperature, enough to trigger melting. ecentricity raised to 0.1
tidal heating would have lasted for 10^8 year
clathrate has a lower conductivity than pure water, and so could have acted as an insulator, increasing temperature further
tidal heating produces stresses because it occurs over long enough times span >10^7 yr) that a cold surface is always preserved
Only ice meets the criteria for volume shift between phases to explain the surface features
grabens or continental rifts, consistent with extensional tectonics
scarps lining the rifts form much of the outer banded zone of Arden
ripples in the coronae may be compressional wrinkle ridges
tidal or radiogenic heating of 100 to 150 k produce a 1 to 1.5% volume expansion
melting and refreezing of all the water on Miranda would produce a 4-5% expansion
"sinkers"; high density anomalies sinking into a viscous aesthenesphere, though this hypothesis is difficult to prove at present, since effects predicted by the model are determined by factors as yet uknown, such as the thickness of Miranda's crust
diapirs: rising, low density material
depends on the strength of the lithospheric matierial
Elsinore contains unmistakable flow features
pure water is too difficult to heat, and its negative buoyancy makes it a bad candidate for lava
an interior containing clathrate could produce a flood of exotic ices
due to Miranda's lower gravity, cracks would have to be much longer (10-100 km) than those on Earth to allow for extrusion
features suggest viscosities of 10^8 to 10^9 P
stochastic
Bauer 2002[edit]
the near infrared spectrum of miranda: Evidence of crystalline water ice
rock mass fraction of 0.2 to 0.4
Coronae: relatively uncrated regions 200 to 300 km across surrounded on all sides by extensional rifts
Probably tectonic features that have been modified volcanically
a fluffy porous surface may indicate a history of bombardment
darker material may be polymerised ch4
miranda's composition cannot be pure water because the temperature necessary to melt it would have erased any earlier surface features, visible in cratered terrain
passing into a resonance with umbriel may have heated miranda's core to 200 k from 80 k (not enough to melt a pure ice body the size of miranda
If the water+ammonia cryomagma were a solution of more volatile substances, such as nitrogen methane or carbon monoxide, then the magma would have been loaded with gases, whcih would have led to explosive volcanism, of whch there is no evidence. Ammonia would leave traces on the surface, but has not been observed. Methane would have evaporated off completely within a few million years
Arden corona shows the most compelling evidence of surface flows
1.65 micrometre signature of crystalline water ice indicates heating events in excess of 100 k
Triton shows evidence of cry. water ice, despite half temperature (40) but no evidence of ammonia
Charon possesses ammonia, and is a better fit for Miranda than Triton
corbonaceous or silicate contaminants at 70% to lower albedo
best fit suggests a 3% ammonia solution
Presence of NH3 would favour the spin out model
Hammond, 2014[edit]
global resurfacing of Uranus's moon Miranda by convection
Catastrophic disruption has faded as an explanation for the coronae
Most astronomers accept diapirism
How tidal heating could have led to the observed surface formation has not been well described
Models of arden suggest an elastic thickness of 2 km and a thermal gradient of 8-20 k per km
past heat flow of 40-100 mW per m2
radiogenic heating is not expected to be significant
3:1 orbital resonance between Miranda and umbriel can explain Miranda's orbital inclination
Might have generated 5 GW of power; lowered ice viscosity and created a thermal gradient
models suggest that ice viscosity is so temperature dependent that it would be confined below a frozen stagnant lid
convection could have broken through the lid if its yield stress is 10kPa
Yield stress of ice may be up to 1 MPa, suggesting that tidally flexed surfaces may be anomalously weak
The number and arrangement of convective plumes is affected by core size, viscosity structure, Reyleigh number, and the distribution of tidal heating
A core radius of 0.25 can sustain convection over the widest range of rheological constraints
low order convection and surface reyleigh numbers between 10^2 and 10^3.5 creates a thermal gradient consistent with surface flexture estimates
Convection produces the concentric patterns seen in the coronae, as crust moves away from the plume heat source
The positions of all the coronae require a tidal heating pattern cinsistent with a world with no ocean
Plumes are formed near the equator, so a reoirientation is required
A 60 degree rotation from the sub-uranian point, possible solution for skewed impact crater distribution
Aristotle[edit]
Comets, meteors and the Milky Way are all discussed in Meteorology
sublunar region of generation and corruption; earth air fire and water
celestial region: unchangeable, incorruptible, aither, ungenerated, indestructable and cannot be altered or increased.
"In the whole range of time past, so far as our inherited records reach, no change appears to have taken place either in the whole scheme of the outermost heaven or in any of its proper parts.
Earth at the bottom, then water, then air, then fire
Hot dry exhalations from the earth rise to the top of the sub lunar region, forming a region of fire above the region of air
this is not fire as in flame, but a kind of "protofire", which is capable of being enflamed. Later philosophers would call this phlogiston
Exhalations from the Earth are ignited by what we would now call friction due to the fire layer being dragged by the motion of the celestial sphere
1. Planets are in the zodiac, comets are not always
2. two comets can be seen at once
3. they are not among the 5 planets.
Comets were basically giant shooting stars, from a learger exhalation, slow burn
If comets' tails were due to the movement of the sphere, then they should always be seen pointing westward, and yet they always point towards the sun
Seneca= comets rise and set with the planets and stars, merely scattered outward.
comets had been visible for mroe than six months
seneca asserted that the reason comets fade is not because they burn out but because they are farther away. Would exhalations follow such stately trajectories?
"Who places one boundary for planets?" Even the planets have orbits that are different from one another
Seneca ultimately failed to develop his own theory of comets, such as explaining comets tails
Ptolemy considered comets sublunar phenomena
Olympiadorus: Milky Way does not have parallax, moon does. Also if it were the result of exhalations, its appearace would vary across the year
Ptolemy treated comets as omens heralding unfortunate events
"Teh fact that comets when frequent foreshadow wind and drought must be taken as an indication of their fiery constitution
Tycho[edit]
save the appearances (ptolemy would have looked through Galileo's telescope)
Married a clergfyma's daughter- could ot pass his estates to his children. Some in the family outraged, others grateful that the wealth would stay
lunar eclipse 1566 tycho wrote a poem proclaiming the death of Suleiman The Great. He was already dead. His cousin teased him about it and Tycho challenged him to a duel.
a gold and silver nose, alloyed to flesh colour, copper in a pinch, held on with adhesive salve.
1572: New star stella nova, brighter than Venus, age 25
"let all philosopehr's ew as well as ancient, be silent! Let the very theologians, interpreters of the divine mysteries, be silent! Let the mathematicians, describers of the heavenly bodies, be silent!"
parallax on different points on teh Earth's surface, moon showed it, the nova did not
no greater teacher of theology than the universe itself
alter baade determined type 1a
Uiversity was the province of the middle classes, bishops, scholars teachers. Tycho had never intended to pursue a academic career, until De Stella Nova
imagiary time, quark charges,
Tycho idolised copernicus but refused to countenance a moving Earth without parallax
Frederick the Great offered Tycho a chance to fund the costruction of a astronomical research establishmet on the island of Hven (After Tycho had refuesed his offer of other castles as beig a destraction from his work)
uraniborg, castle of Urania
13th nov 1577, a comet observed.
A series of bright comets after 1531 led to the realisation that a comet's tail always points away from the Sun
diurnal parallax: using the rotation of the earth (or celestial sphere) to shift your location relative to a more distant object. The moon is close enough that its parallax is one degree. Thus anything with no observable parallax or smaller than the moon must be farther than the moon
"This mieracle [nova] has made it nec essary for us to abnandon thje oppinion of aristotle and take up another: that something new can also be born in heaven... The superior Penmtates at certain times ordained by God , fabricate such new stars and comets out of the plentiful celestial matter and display them clearly before mankind as a sign of future things." Brahe
Martin Luther [brahe was a Lutheran] believed that comets were ordained by god to instil terror, as a sign of the last days.
tycho, comets refract sun's rays
Comets do not orbit the Earth and are not periodic
comets being not as perfect as planets, do not have uniform, circular motion
Tycho Brahe's instruments gave him a tenfold increase in accuracy
Tycho's observations killed Aristotianism dead.
The apeparance of three comets in 1618 formed part of a "great debate" between the followers of Tycho and Galileo.
grassi: comets are moving in a great circle that onyl appears linear when projected onto the celestial sphere
galileo said that comets could not be similar to planets, as planets rise and fall in brightness periodically as they approach or retreat from the Earth, wheras comets begin as bright and then gradually dim
comets could not be fiery objects as the celestial spheres would be cold and douse any flames
Comets were mere appearances, reflections of exhalations from the Earth. This concept didn't even last Galileo's lifetime.
Tycho's sextat was gilded with the fineries of nobility, yet aslo with reminders of its impermanence, a skeleton a withered tree. "By the sprit we live", the rest belongs to death".
tycho became a canon of the chapel housig the body of Fredericks' father. When it was demaded that he reouce his clame to the rents from land in Njordford, he refuse, ad was allowed to keep it. This sent Tycho's ego dangerously out of cotrol
He would often whisper the names of students only for them to appear as if by magic (he had in fact already called them on a bell pull)
His peasants were worked to the bone supporting Uraniborg, though Tycho arguably was no more cruel to them than he was allowed
There is nothing more problematic than a well-founded ego.
His istruments took six trained peopel three years to make
He had his own state of the art workshop on site
Tycho observed that, after observig the comet at the same point in time 24 hours later, the comet had moved 3 degrees of arc. Give that speed, then if future measuremets showed that its position was more or less than that predicted by its speed, it had to be due to parallax shift. The comet showed virtually no parallax at all, indicating it was not a meteor
Castig brith horoscopes for Frederick's Children, analysing portents in astral phenomena
the largest armillary that had ever been built
Styerborg star castle. subterranean observatory bedeced with crowned lions and inscrioptions praising Brahe
"tychonides", his future descedant would be his successor
Tycho was intensely meritocratic, and elevated promising lower class people whose talent he recognised. Tycho would often throw people with whom he disputed or their families into his own dungeon. Did they observe any of his alchemical practices?
Christian some of Frederick I visited Roskilde Cathedral in 1593
Tycho did the job of an aristocrat, holding splendid court and entertaining guests, very well
Christian was crowned in Roskilde chapel
Christian was a fan of the fad for autocracy currently sweeping Europe, and disliked Tycho's lack of deference
In 1597, Tycho's pension from the crown was discontinued. Uraniborg was closed and he moved his materials to his house in Copehagen
Tycho was gaining enemies, from the University of Copenhagen who felt he was a drain on their material and human resources, and from theologians who were less inclined towards science, or to his unconventional wedding
the peasants took advantage of this and began to complain that he was abusing his canonry
Tycho was ordered to remove his instruments from his roof, as they obstructed the King's view. He became a laughing stock at court
Tycho was exiled, essentially, to Rostock. The peasants eventually raised Uraniborg to the ground, leaving not a trace behind. Tycho the evil lord who had built over their pasture was a curse in Hven until the late 20th century
Halley[edit]
astronomy was considered mathematics, not physics
first paper while still an undergrad at Oxford. A mathematical proof derived from Kepler's laws of motion
Flamsteed: First Astronomer Royal. Flamsteed designation, Greenwich observatory under construction
By tracking the motions of sunspots, Halley and Flamsteed calculated the rotation of the Sun at 25 days, 9.5 hrs (25 days 0hrs 7 min at 16 degrees latitude)
Halley would destroy the fiction of the celestial sphere by showing that over thousands of years, stars have proper motion
By the time of Halley's education, telescopic sights had rendered Tycho's catalogue obsolete.
At the age of 20, Halley undertook an expedition to St Helena, (he declined Rio de Janeiro or the Cape of Good Hope for fear of not grasping culture and language) only to find the weather almost constantly cloudy and rain soaked
Just 341 stars, first telescopic catalogue in print
He noted that the Magellanic Clouds had the same colour and clouds as the Galaxy (ie the Milky Way)
In 1684, His father, having suffered financially from the Great Fire, committed suicide, forcing Halley to abandon his astronomical observations for a salaried position
The Royal Society demanded that Halley print the Principia at his own expense, despite his financial difficulties
He also served as Newton's editor and corrected the proofs
James Gregory, solar parallax transit of Mercury, Halley on St Helena,
He was Savilian Professor of geometry at Oxford
His father was a Yeoman Warder
Halley's first patron after his father, Jonas Moore, was Surveyor general of the Ordinance, a position headquartered at the Tower, and would play a pivotal role in the founding of the Royal Observatory at Greenwich, which Halley would eventually run.
Moore's staff likely manufactured Halley's instruments
Hooke's plan for the reconstruction of London after the fire were accepted and he designed the replacements alongside Christopher Wren
Hook had a habit of coming up with ideas and not following them through, which led him to accuse others, particularly Newton, of stealing his credit.
Charles's Oak- new constellation planisphere, dropped after 50 years because it "stole" many stars from Carina and Argo Navis
Halley was the first to work out a practical method for determining solar parallax from a transit of Mercury or Venus
He observed glitches in the orbit of the moon which Newton would show were due to the gravity of the Sun
first telescopic catalogue with a micrometer
Flamsteed called him the Southern Tycho
post principia, Halley attemtped to measure the length of a degree to learn the size of the earth
Hooke identified the Comet of 1664 with the comet of 1618. Cassini had identified the comets of 1577, 1665 and 1680
In 1681 Halley observed the Great comet of 1682 alongside Cassini. Was it the same comet as teh Great comet of 1680? did it move behind or in front of the Sun? Was it the same comet seen by Tycho in 1577?
Queen Christina had initially seen comets as omens of evil, and may have abdicated the throne of sweden after a supposed cometary warning, but by 1680 was offering prize money to anyone who could calculate its orbit
Halley's observations, directly or via flamsteed, would provide the data for Newton's chapter on comets
Newton calculated that the paths of any comet around the sun would be an ellipse due to the inverse square law
Halley's clerks salary was paid in copies of an unsalable book, the history of the fishes, the failure of which likely led to Halley having to shoulder the cost of printing the Principia
Newton letter to Halley, stumped on comets (III), not beholden to Hooke, considered suppressing it
his mother and stepfather sued him?
Halley and flamsteed's relationship soured, first over scientific disagreement, then over real or imagined claims that associates of halley were spreadng lies about him,
The orbits of the planents could be simulated using ideas without gravity, but comets could not be explained without it
Halley's comet marked the death of Agrippa in 12 BC, the defeat of Attila t Chalons in 451, and the Norman Conquest
comet fortetold the death of Julius Caesar
Newton initially thought Newton's comet was two different comets, Flamsteed did not, and never let Newton forget it
Halley also surmised that the comets were the same and believed that the sun "repelled" the comet
In 1695, Newton and Halley met to discus redoing the calculations for comets in the Principia
Halley was able to construct a table in which the position of any parabolic comet could be obtained for any position after perihelion.
in his observations, he wondered if the comets of 1531, 1607 and (later) 1682 were the same
He did however remind Newton in his letters that the gravity of Saturn and Jupiter could change a comet's predicted date
Halley was prone to sea voyages, and Newton had been appointed head of the Mint
Clairaut calculated for return of halley's comet
Astronomicae cometicae synopsis- 1726 edition; Halley asserts for the first time that the comets of 1682, 1607 and 1531 were the same, and speculates that the comets of 1456 and 1305 were the smae (they were). He predicted the comet's return for 1758.
Halley died in 1742
Charaut made the mathematical advances required to calculate the perturbation by Saturn and Jupiter
Some astronomers saw the work involved and simply gave up. Lalande and Lapaute did the work of the calculations
Perigee was a month earlier than predicted (1759)
"the Universe beholds this year the most satisfactory phenomenon ever presented to us by astronomy; an event which unique intil this day changes our doubts to certainty and our hypotheeses to demonstration" Lalande
Halley was the first to suggest, by studying Arabic records, that the moon may be speeding up and receeding from Earth
Halley, by applying Newton's laws to everyday, testable phenomena, was able to ground Newton and make him useful, moving him away from the accusations of mysticism and atheism that had so dogged his work.
halley and flamsteed historia coelestis
1676: Flamsteed and Halley had fallen out
Newton[edit]
robert Hooke: "may be fo the same nature and constitution with that of the internal parts of the earth.
The tail "is much of the same nature of the parts of a flame"
Newton concluded that the nucleus of a comet would be about a tenth to a fifteenth the size of the coma, and since that is smaller than Saturn and comets are seldom brighter than saturn, comets could not lie beyond Saturn's orbit.
Comets are free to move in any direction, whether tied to the orbits of the planets or not.
"the heavens are lacking in resistance"
At the comet's distance from the Sun at perihelion, it would be receiving 28,000 times as much heat from the Sun as Earth. At such temperatures, a vaporourous or daphenous comet would be anhillated. Comet nuclei must be durable, solid and dense. the closer a planet to the sun, the denser it is; ergo a comet that passed between mercury and the sun would be denser than Mercury. comets are the sens
a comets tail forms from interaction with the come's atmosphere, the suns heat and the particles of the ether (Kepler, only sun's rays)
comets are the densest opbejcts in the solar system
If the comet were a refracting beam, then it would be refracting off some atmosphere in the heavenly region, but the ether did not appear to have this refractory ability.
Tails grow longer as the comet approaches the sun; therefore there must exist a relationship between the length of a tail and the proximity to the sun
the vapours of comets attracted by planets mix with their atmospheres and provide ingredients for the sustenance of life (rain risen by the heat of the sun, falling on planets)
Newton speculated that comets moving too close to the Sun would be slowed down by its atmosphere, and that collisions between comets and stars may be what produces novae
Newton believed that comets could destabilise the Solar system with their chaotic orbits, until such time as God willed a reformation.
Newton said very little bout what this ultradense substance might be
a comet heated to 2000 times the brightness of incandescent iron would rarify its own atmosphere while making the nucleus shine
Newton made it possible to plot the orbits of comets precisely, and opened the way to a new form of cometary prophecy
comet caused the deluge= 8000 miles in diameter coma 100 000 miles
Kant nebular hypothesis; all the universe a large scale model of the solar system
Galileo believed that comets were optical illusions
william whiston: comests eere vast, 7-8000 miles in size, and the earth was originally one. A close approach of a comet in 2349 bc led to the biblical deluge
tail formation was newton's achiles heel
newton believed that the ether carried the particles along
but the barticles of a comet were heavier and bigger than ethereal particles
why did comets with perihelia close to the orbit of venus produce tails, when venus did not?
Newton did not believe the sun's rays played a role in the formation of cometary tails, curious
Post-Newton[edit]
Immanuel Kant, in a remarkable bit of prediction, noted that comets originated in the farther parts of the solar system, where accretion rates were too low to form into planets
He argued that comets were a natural part of the formation of the Solar System, and were as old as the Solar System itself
He argued that it was the sun's light, rather than its heat, that was responsible for the creation of a comet's tail, since comets had formed tails far from the Sun.
Comets had to be composed of light materials, light enough to be affected by the Sun's light
He also argued that the same phenomeneon that created a comet's tail also created the aurora borealis (a common speculation at the time)
Kant's book's publication was delayed for a decade after his publisher went bankrupt. By then it was overshadowed by his other philosophical materials.
In 1770, Messier discovered a comet Orbit calculated by john lexell
only 5 years How had it not been observed before? orbital calculations showed that its original orbit had been altered by the gravity of Jupiter
Leplace studied Lexell's comet's orbit, close enough to affect earth's orbit, and found its effects on earth's motion to eb negligible (if it were the sixe of the Earth, it could be expected to affect Earth's passage around the Sun by 0.1 days- <1/5000 the earth
Lapace concluded that teh actions of comets on planets, even impacts, could not have affected planetary orbits.
Laplace rejected Kant and said that heat must play a role in the formation of tails, and that comets must be made of exceptionally volatile matter to be affected so far from the sun
Laplace concluded that exposure to the sun's heat could not entirely destroy a comet, just as raising a liquid's temperature to boiling did not immediately evaporate it, but after a few revolutions it would be destroyed, just as lexell's comet had apparently been
length, straightness, bluish color (ionised carbon monoxide), radial alignment (plasma tail)lapace
lapace calculated that the chances of the planets, satellites, sun all sharing the same rotation is about 40 trillion to one. therefore they must share a common cause. Comets's orbital direction was essentially random. However their inclinations averaged about 45 degrees, leading laplace to deduce that they must have originated in interstellar space.
A comet impact could be disastrous, but Earth could have passed through a comet tail numerous times without noticing
Herschel confirmed Lapplace's estimates for the sizes of cometary nuclei
Herschel: If comets shone by reflected light, then they would display phases like the Moon or venus
Francois Arago, 1819, polarised light, comets showed it, stars did not, which meant they had to shine at least partially through reflected light
David Milne 1828: fears concerning the moral influences of Comets, the production of a weak and debasing superstition, have long since been rooted out from the faith of enlightened Europe, btu they have disappereed only to be succeeded by others, respecting their physical influence
Bessell's jet hypothesis vs slowing medium for the slowing of comet encke; 2nd periodic comet, encke believed in the resistant medium. such a medium would have effets on every body in the solar system, unresolved
Bessel, halley 1835 eruption in the direction of the sun, noticed that the axis was occillating
I consider it probable that a comet's nucleus is not a really solid body; ie not a solid body of the same kind as the earth, the moon and the planets. It must be able to go easily through a state of volatility, whereas the above mentioned bodies do not possess this property or at lest possess it to a lesser degree.: the fact that its surface does not show a sharp boundary suggests that Comets consist of parts which become volatile when under the influence of heat or of some other repulsive property- bessel
Comet biela was the first to observed to split (second jup comet)
the fact that Biela's two parts did not attract each other suggested they were of exceptionally low mass
The comet did not return when predicted, however, instead, a heavy meteor shower fell
that short period comets were linked to meteor showers was established in the 1860s
Schiaparelli determined a link between comet swift tuttle, tempel tuttle and Biela Herschel: If comets shone by reflected light, then they would display phases like the Moon or venus
Francois Arago, 1819, polarised light, comets showed it, stars did not, which meant they had to shine at least partially through reflected light
Donati's comet 1858 visible for four months (9 months telescope)
formed three tails, two like antennae
the comet appeared to form dark bands separating the coma into stripes. This, according to George Phillips Bond, could only be happening if the nucleus of the comet were rotating
In the mid 19th century, experiments with electricity showed that when electric currents were passed through a very rarefied gas, such as that which existed around a comet, it produced an effect similar to that of a comet's tail.
the tail was produced by a repulsive force emanating from the sun William A Norton called it "the repulsive force of the Sun" (not sunlight)
the tail and the nucleus were not one body, but comprise particles emanating from the nucleus, which exist as a tail only for a certain time
James Clerk Maxwell (elec and mag) outlined how light itself could exert pressure on a surface suspended within a vacuum Using an incredibly sensitive machine, Russian physicist Peter Lebedev detected light pressure in 1898
In the early years of the 20th century, Svante Arrhenius applied discoveries made a decade earlier in cloud chambers, that high energy light such as ultraviolet and xrays could ionise gas and make it electrically conductive, allowing the comet to luminesce despite its low temperature
Karl Schwartzchild calculated that for comet particles to be affected by light pressure, they must be of a size comparable to the wavelengths of light, otherwise light pressure would be overwhelmed by the Sun's gravity; a calculation that was later verified in an experiment with fungus spores
repulsive force 100 times stronger- biermann- solar wind
jet effect on comet encke, shortened its orbet, expanded halley's
In 1866 William Huggins made the first detailed spectra of a comet, Tempel 1. In 1874, the arrival of Comet Coggia allowed Huggins to securely identify carbon in the spectra and connected it to hydrocarbons found in meteors and meteorites
Carbon carbyne, carbon monoxide, hydroxyl cyanogen N2 found in Coggia and in Halley's Comet in 1910
Many of these particles were ions, suggesting they must have been stripped from larger molecules
In the 1940s, Polydore Swings studies of emissions led him to conclude that the precursor molecules that formed the ionised coma material comprised ammonia, methane, cyanide, nitrogen, carbon monoxide, carbon dioxide, and water.
1950, 1951: Fred whipple,icy aggregate of comet material, dirty snowball
ices vaporise at perihelion, dispersing meteoric material below a certain size. Meteoric material above a certain size remains and forms an insulating layer, which eventually reduces the loss of gas
a comet was layered by ices in order of volatility, with water and meteoric material at the bottom
clark[edit]
1 sep 1859 bright light, as bright as lightning but rounded instead of jagged. Brighter than the surface of the sun
"flurried by surprise" "unprepared to witness" it.
the ligths had lasted just 5 minutes, but had traversed 35,000 miles (420 mph< an absurd speed for a victorian
18 hours later auroras erupted all over the world, as far nroth as acuncion, as far south as massechusetts bermuda and Georgia, then jamaica and cuba
confermation came from the magentometer at Kew, which showed that compass needles were jarred away from true north at the exact moment he noted his explosion, an even stronger one eighteen hours later
auroras all across europe for days
disabled the telegraph system, telegraph operateors got severe electric shocks
electrical currents caused the paper at telegraph offices to catch fire, nearly destroying the buildings