User:Serendipodous/indigo/page 26

future

Ah, here we go. Jean Meeus wrote about this in Section 6.3 of More Mathematical Astronomy Morsels. He points out that the tropical year is the time for the sun's mean longitude to increase by 360 degrees, which is not quite the same thing as the time between one March equinox and the next (which Meeus calls the E-E year). Both years are variable in length, with the tropical year currently decreasing and the E-E year increasing. At J2000.0, the tropical year was 365.242190 days, while the E-E year was 365.242375 days, closer to the mean Gregorian calendar year of 365.2425 days. The E-E year hangs around close to the Gregorian year for the next few millennia, so (according to Meeus) the accumulated mismatch between calendar and equinox would amount to only 0.26 days between 2000 and 8000 CE. However, the Earth's rotation is slowing, with a cumulative mismatch between Dynamic Time and Universal Time (all those leap seconds). That effect, superimposed on the pretty small mismatch between the E-E year and the mean Gregorian year, means that (according to Meeus) we will have accumulated a one-day mismatch between equinox and calendar by about 7200 CE (but with a strong dependence on the rate of slowing of Earth's rotation during that time).

sr.gr

GR means TAI estimations ahve to be calibrated for height above sea level

1.09 parts per 10 trillion per km above sea level

GPS satellites are affected by SR (they move) and GR (they are aboce sea level)- -7.1 ms/d GR, +45.7 ms/d SR

Panfilo

International Atomic Time (TAI) was established in 1971 by the Consultative Committee on the definition of the second

13th general conference on weights and measures adopted the atomic definition of the second in October 1967

UTC is TAI plus leap seconds

Definition cesium atom cycles at absolute zero

UTC is meant to approximate the rotation of the Earth for geodesy, satellite tracking, celestial navigation

GPS and GLONASS have spread UTC throughout the world

TAI instability is calculated at 3x10^16 over 30 days and 7 or 8 x 10^16 over a decade

UTC is published monthly in data batches by the BIPM, not in real time

2 ms over 120 years. In 600 million years, the Moon will be too far away for total solar eclipses to occur, and the day will be 27 hours long.

Nelson

UT1 is used for astronavigation

It was not until the fourteenth century that an hour of uniform length became customary due to the invention of mechanical clocks.

For example, several corals dating from the middle of the Devonian Period, some 370 million years ago, indicate that the number of days in the year was between 385 and 410

The rotation of the Earth runs slow by about 30 ms in May and runs fast by a similar amount in November. thwe babylonions divided th day and night into 12 hours, varying in length with the seasons, with the sixth hour indicating noon

Greenwich mean time originated from the railways

sidereal vs solar day: Earth has moved in its orbit

the moment the Sun croses the celestial equator, the equinox, has been used since the beginning of western history to mark the length of the year

nutation and interactiions with the other planets vary the length of the equinoctal year by as much as 18 minutes

bradley's nutation

UT1 earth's rotation

UTC Est 1/1 1972 UT1 plus leaps seconds

Leap seconds are added either on Jun 30 or Dec 31

Magellan had suffered mutiny, starvation, and shipwreck, one of his ships, the San Antonio, simply left and was never seen again. One of his mutineer captains he left to die in Patagonia

Straits of Magellan

He eventually took a poisoned arrow in the Philipines and died

Elcarno had seen his crew imprisoned by the Portuguese (he himself hightailed it out of town) and one of his ships sailed across the pacific to Panama, only to have to make another crossing

"How angry must god be with us for celebrating his holy days on the wrong days!"

On Santiago, the locals insisted it was thursday the 10th of July, when Elcarno's log showed it was Wednesday the 9th

The local authorities insisted on their own ruling, even after gaspari Contarini assured them that losing a day was a natural consequence of circumnavigation

splitting the second Jones

Ut was established using sidereal time, stars a re easier to monitor than the sun

the sidereal day is 236seconds shorter than the solar day, because the solar day accounts for the earth's motion around the sun, which delays its timing

the amount adds up to one day a year, so a sidereal year is 366 days

the change was fixed into the definition of UT sidereal calculation solar result

In 1695, Halley discovered, through the timing of ancient eclipses, that the speed of the Moon had increased over time

50 years later as tronomer richard dunthorne confirmed that if the radings were true, the moon had dirifted forward by two degrees in the previous 2400 years

attempts to confirm this cotinued for a hundre years, until it was realised that the earth's rotation was decellerating

eventually it was realised that this deceleratiion was due to the moon, specifically tidal friction

but the moon remained eratic, sometimes ahead, sometimes behind, on the scale of decades

1939: Herbert spenser jones astronomer royal, showed that theexact same discrepencies were seen in the sun and in mercury

chandler's wobble 428 day

the rotation of the earth differed by a milisecond between spring and autumn

1927 andre danjon, use time based on the motions of the planets, the year rather than the day

1950 gerald clemence of the us naval observatory presented the idea of the sun's positio, measuired against those of the planets, to tell an absolute time. This measurement of time, called ephemeris time, was officially adopted by the IAU in 1952.

1956: SI units the second defined as 1/31556925.9747 of the tropical year 1900 as measured from midnight GMT on 31 December 1899 Ephemeris time

shortt clocks, two pendulums in a vacuum electriccally linked, could keep time to two milliseconds per day and were the standard scientific clocks of the 20s and 30s

1927: quartz crystal ocillator

A quartz crystal when struck rings like a bell, because of its piezoelectric properties, this produces an alternatuing electric current of the same frequency

the frequency is dependant on its cut and size, usually 32768 hz, the 15th power of two, so it can be evenly divided until a second is counted

most modern qarz ocillators contain microprocessors that adjust for changes in temperature

all battery powered clocks, smartphones, laptops have quartz ocillators

lord kelvin noted that atoms absorb and emit light at specific frequencies, and that these could be used as a time standard

hydrogen waves travel at 100 quadrillion hz, not a number easily counted.

However, the electron/proton do have a dipole, which shifts depending on the orientation of the electron. If the poles are aligned, electron oves up, if not, electron move down. This shift occurs at a frequency of 21 cm or a measly 1.42 billion hz

this is known as the hyperfine state for the ground state

alkali metals possess a single electron at the top shell

Caesium has a spin flip transition of 3.26 cm, or 9.2 billion hz, still countable but enough to allow fine gradation

this lay in the microwave spectrum,. and radar was now availabe as war surplus

Caesium has only one naturally occurring isotope, so unlike most elements, which ciome in isotopic stews, caesium atoms are all identical, atomic mass 133

low boiling point yet hyigh mass forms a sluggish vapour

caesaium is the heaviest of the radiologically stable alkalis, meaning that its electron is very easy to knock off.

the first successful caesium clock was constructed in 1955 at the national physics laboratory

the clock uses a "beam" of caesium atoms, filtered by magnets into hyperfine states, then hit by two ahortr bursts of photons at 9.13 ghz, causign them to flip

the unflipped atoms are then magnetically sorted and sent to the bin

a red hot wire knocks the electrons off, then a metal plate catches the charged ions

the more ions hit the plate, thje stronger the current

when the current was at peak, that meant hat only flipped atoms were being coutnied and so the current had to be the same as teh microwave frequency

9192631830 cycles per second (mean solar second, as per the greenwich observatory) +-10hz

No other quantity had ever been measured so accurately

quartz crystal clocks calibrated to this frquency became accurate to one part in 5 billion

to obtrain a measurement of ET to that accuracy would require four years of lunar observations

UT0 vs UT1 vs UT2

the atomic clock was first sold to teh IAU as an accurate means to tell ephemeris time

the length of the second was increasing 50 times faster than tidal friction predicted

...770

In 1960, the ET second had become an SI unit. a group of observatories and oaboratories agreed to a UTC, a universal coordinated time, to be adjusted every year or so to bring atomic time in step with epheeris time

October 1967: the general conference on weights and measures defined a second as the duration of 9192631770 cycles o the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom

two clocks never keep precisely the same time

A world clock can never stop, but all clocks must stop. Even a cesium clock runs out of cesium

how would we know which clocks are right?

International atomic time

Coordinated universal time - to run telecommunications

1 Jan 1972 established

Tai is the endless caesium tick. It is calibrated by 260 clocks calibrated to fewer tha a dozen frequency standards

Utc is the civil time, like gmt until the 1920s

It is tied to the rotation of the earth

Between 1958 (when first synchronised) and 2000, TAI and UTC drifted by 32 seconds

The accuracy of these clocks ranges from one part in 10^13 to two parts in 10^15

the length of the second is known to 14 decimal places, the most accurately measured unit

hydrogen maser clock more accurate over a period of a few days

GPS coordinates the clocks

these clocks are not meant to tell the time, but to measure the length of the second. tai corresponds to the si second to within 4 parts in a quadrillion

49 timing centres produce UTC

different versions of utc are expected to be within 1000- 100 ns of UTC as calculated by BIPM; most do not make it to 100

changing to correct teh UTC (steering) is gradual and takes weeks

in the 1980s, errors coudl amount to microseconds, but today they are in tens of nanoseconds

1975 GMT was replaced by UTC

uk still runs n gmt although everyone taht matters uses utc

1997 bill to change to utc ran out of time

Intrnational earth rotation service

IERS defines the earth and celestial reference frames

Verty long baseline interfeometry: linking radio telescoes thousands of km apart so they can form a larger telescope

they can then be used to determine the positions of quasars far more accurately than a star

teh orientation of the telscope array with respoect to the quasar can be calcualted to within a milliarcsecond

buzz aldrin left an array of 100 light reflectors on the moon

nedium to longeterm changes in the rotation have no pattern and can vary by up to 4 milliseconds

day is lengthening tidal drag 2.3 ms per century

rebound since the last ice age has shortened the day by 0.6 ms per century by makign the artrh more spherical

movements in the core of the earth and changes of sea level can change the rotation by 4 mas per century either way

tidal drag is negligibole for everyday timekeeping

the most troublesome changes are those which occur on the scale of decades and are mostly caused by changes in the flow ofthe liquid iron outer core

these motions create the magnetic field and by studying it scientist can determine what is happening

teh flow is random, and is likely caused by the magnetic field pulling on the mantle above

the warth spins slowest in autumn, and speedu up in mid summer NH

this is most likely caused by changes in atmospheric circulation throughout the year

winds pushing against mountains can slow the rotation of the earth by a noticable amount

in 1983 the earth day lengthned by a ms for a few weeks, timed to el nino.

1972 leap seconds initiated

all 22 have been positive so far

end of months dec jun preferred

the earth is actually speeding up, and has been for several years so why leap seconds?

because ut1 was established in the early 19th century

time is tramsitted by longwave radio from UTC cenrres which are far more accurate than short wave

GR means TAI estimations ahve to be calibrated for height above sea level

1.09 parts per 10 trillion per km above sea level

GPS satellites are affected by SR (they move) and GR (they are aboce sea level)- -7.1 ms/d GR, +45.7 ms/d SR

leap second

Yeah, I think the story of the leap second is sometimes summarized down to such a condensed state that it's difficult to understand. We do have leap seconds because the Earth's rotation rate is slowing, but the reason we have so many is because of the way the duration of the second was defined and then redefined over a long period of time - at first astronomically, and then switched to a definition in terms of physics. This meant that the SI second (when defined physically half a century ago) was based on the length of the day as measured by astronomers a century previously. Hence the 2ms mismatch we now enjoy, which brings the leap seconds around fairly frequently. The other problem is that the average slowing, of 1.4-1.7ms/dy/century, obscures a relatively large amount of year-to-year variation, which is of magnitude comparable to a second - so the leap-second interval can come more or less frequently than what you'd predict from the simple 2ms average daily mismatch. There's even the potential to need a negative leap second, but we haven't reached that threshold so far.

One time fits all bartky

Wednesday 9th of July 1522, Victoria, with thirty broken, ravaged men arrived at Portuguals Cape verde islands

the last of magellans 5 ships and 285 men

juan sebastien del cano

they were toled it was thirsday but by their count it was wednesday

Antonio Pigafetta the diarist and francisco albo, the pilot had kept meticulious journals, and disagreed as to whether they had made a mistake

Because they had chased the sun westward, they had tripped it up in its passage very slightly, meaning that for them, it set ever so sligfhtly later than for confused landlubbers. As they had circumnavigated the globe, the difference added up to one whole day

"one ought to assign a definite place where a change in the name of the day would be made." oresme 14th centuroy

Teh spanish counted time west of Cadiz, the Portuguese east of Manila. Cadiz and Lisbon are about 3 minutes apart in time, Manila and Macau about thirty minutes. Yet noon in Manila oxccurred 15 hours behind Cadiz (westward) and while noon in macau occurred eight hours ahead of Lisbon (eastward)

since latitudes were calculated employing almanacs showing the sun's position in the sky at fixed days, the day error could lead to failures in navigation

When the descendants of the mutineers of the bounty were finally rediscovered by the American captain Mayhew folger, they were found to be keeping time one day in advance of the arriving vessel

the bounty had attempted to reach tahiti round cape horn, which is one of the most inhospitable regions in the world. and had abandoned it and instead made for the cape of good hope. the later arrivals had all come by caoe horn

ottos struve's meridian report

by the 1860s 14 different base meridians were being used on topographical maps

the date line had been establlished via convention (eastern vs american) but not by fiat

an international standard map woudl require an agreed projetion , latitude longitudes boundaries, symbols legends

as long as empires kept consistent within themselves, this didn't really matter

ordinence survey were the only ones to print the proposal (sir henry james)

france used paris, spain and protugal still used lisbon and cadiz, but everyone else already used greenwich. This was simply because britian produced the best hydrographic charts and maps, to the point at which bothering to produce your own was pointless

Urbain le verrier had refused the paris observastory employ French maps due to thier errors

ferro meridian avoided bisecicting europe (though not iceland) 20 west of paris

With the anti meridian in the pacific, it would inconveience virtually no one

in 1871, the first ever international geograpuhical congress voted that the greenwich meridian should be universally adopgted, though it had no power to enforce the decision

Ironically, the fact that the london and paris meridians were so similar (2 20) made errors far more likely

the nautical almanac was the choice of sailors worldwide

A french counter by adreien germain argued that there was no need for a single meridian, that the dangers were exaggerated, and that a universal code of signals aldready in use included the code "what is your initial meridian?

germain argued that the french almanac, the connaisance, had undergone sufficuent improvemnt to be the peer of the UKs

in 1874 the IGC met again, this time with the meridian excluded from discussion at germain's order It was still discussed

GMT estalished for a small country like britain would not work for American trains

initially train companies used their own times, by the1860s nearly eighty were in use

Charles Ferdinand Dowd, oprincipal of a ladies seminary in sarasota springs new york.

His initial idea was to have the railways use a unified time based on Washington DC

the railway companies rejected teh idea, and soso in 1870 Dowd concieved the idea of four hour zones across the US and canada

He attempted to woo the railroad comapnies byu atending their meetings and printing tracts

his ideas were never taken up and he faded into obscruity

according to legend, in 1876 stanford fleming had turned his mind to rain timetables when, misled by a faulty guidebook, he'd been foreced to wait a day for a train in a village on the west coast of ireland.

fleming was a railway engineer and would have been aware of the train times

fleming was the firt to clearly outline the idea of dividing the world in 24 equal parts each a different hour of time

in 1875 cleveland Abbe realised that he could not fix the time of an auroral display because some of his respondants were using railyway time and others local time

in response the american astronomical soxciey established him as the head of the committee for standdard time and in 1879 it released its report

alll telegraph and railway siystems employ five hou time zones and all local times adjust as well

the anti greenwich meridian was the ideal place for a prime meridian

georgi biddel airy argued that the issues had already been solved- basle had local time, french rail time and germ,an rail time, yet there was no confusion

"i see not the slightest value in the remarks extending though the early parts of fleming spaper"

as for america, simply have trains going from new york on new york time and from sanfran sisco on san francisco time, every station would have a local clock and bingo.

let greenwixch do her best to maintian her high position in administering the llongitude of the world adn nautical almanacs do their best, and we will unite our efforts without special claim to the fictional honour of a priime meridian

in 1881 the IGC met again and decided to come to a final conclusion to be held in washington in may 1882

International Meridian conference

Chester a artrhur asked for ten grand from congress, he got 5

delegates had no compensation

fleming, adams was one of the british delegates

teh french fought for a neutral meridian, bering or ferro

25 countries, 1 oct 1884

"to adopt a single prime meridian for all nations, in place of the multiplicity of initial meridians which now exist" unanimous

simon newcomb argued that there could be no neutral meridian, as any choice wouldhave to be referred to a national obseratory

fleming argued that as most tonnage used the greenwich meridian, an opposing meridian would allow maps to still be useful whilst retaining some neutrality. he was ignored

the french demanded that the meridian be neutral, not passing thorugh any continent. they were defeatd 21 to three with only haiti, a former french colony, and brazil vo9tin with france

fleming attempted to make the greenwich meridian the entire circle, thus leaing room for his anti meridian idea, when adams nformed him the uk governent was opposed he put it to a vote anmnd lost

france again refuse, citing tradition and the expense in changing all their charts

British delegate F J O Evans countered that the admiralty had annual sales of their charts of 100 thousand with 2900 copper plates in use and the nautical almanac topped 15 thousand sales a year

The decision to adopt the greenwich meridian followed frances initial motion- 21 4, haiti brail and france against (brazil and france obstained)

one surprisng debate from a modern persoective was whether to number the meridians to 360, or to 180 eas to west. the earlier conference at rome had suggested th frmer, and most european countries adherred to it, but non-european countries swung the vote. the latter won

the next resolution the adoption of a universal day, was accepted 23 to to abstaining

A final vote, and the msot controversial, was whentehr the beginning of the civil day shoudld bvbegin at midnight at greenwich, it passed 14 to 3 with 7 abstentions

a change to the wording reflectred that scienc and navies would adopt midnight as the standard

as a corutesy to the french, a resolution passed that attempts to decimalise angles and time would resume

unfortunately, the committees recommendations were only dvisory and their implementation stalled in congress

great britain on the other hand, was ecstatic

Japan was one of the few countries to adopt the greenwich meridian immediately

if the united states, the hjost of the convference, could not adopt its recoomentations, then the conference had failed

soon, new universal meridians wee being roopsed, anti greenwich or jerusalem

the hold up was largely blamed on the attempt to shift the beginning of astronomical day from noon to midnight

Newcomb argued that such a change might spell disaster as navigators, not people accustomed to scientific precision, muddled the changeover

the pressure of train timetables led the few large continental powers to decide on a common time, rather than those of their capitals. Germany and Austria hungary both agreed on grenwich plus 1, changing their times by minutes

the balkans shifted to greenwich plus 2

France, when it finally could be bothered in 1891, adopted paris time. Oddly this still applied to its trains, whcih had all adopted paris time anyway, because internal timing clocks were all deliberately set five minutes fast to prevent passengers being late.

even after the adopption of paris time, the five minute delay remained, as the railways were in private hands

attepmts to shift to greenwich were so frught that one even read "paris time minus nine minutes and 21 seconds"

in 1911 the french finally adopted greenwich time, even if they didn't call it that

ironically one holdout was the UK, which had adopted greenwich for the railways but kept to local time in all other things

IN 1880 the UK adopted greenwich mean time

The adopption of the greenwich standard throughout the british empire led to the gradual worldwide adoption of time zones.

By 1916, most countries were on Greenwich mean time with greenwich as teh prime meridian. Even France begurugingly acquiesced in 1911.

On Batille day 2000, the French held a nationwide picnic on the Paris meridian

christie, the astronomer royal, argued that sooner or later large countries like the us would tire of their time zones and adopt a single time, which would lead to the adoption of a universal time

the rise of wireless communication allowed real time communication with moving ships

soon wireless time signals were being employed to determine longitude at sea

by 1910 and the establishment of a longitude determining radio transmitter on the eiffel tower, all opposition to the adoption of greenwich vanished

By 1913, the greenwich maridian was officially adopted by the hydrographic charts of all european seafaring nations

1917 time zones should be extended to the oceans, even though changing time on ship would be massively inconvenient. adopted by the french navy

pilots air traffic controllers space missions and military operations all use UTC

1 jan 1995: kIRIBATI EXTENDS THE IDL MILLENNIUM ISLAND

france maridien internale

Withers

Prior to 1790, different countries had different prime meridians. Britain had greenwhich observatory, France, paris observatory

canary Islands (France) (limit of the western hemisphere) Edward gibbon, most logical "absurd vanity" (English, Greenwich, Dutch, Tenerife, Swedes Uppsala)

British were attempting to fix the meridian at Greenwich, the French at Paris

the first people to attempt to quantify our place in the universe chose their own homes as meridians (Eratosthenes Alexandria, Hipparchus Rhodes)

Ptolemy used the canary islands, but exaggerated the size of the Mediterranean. Islamic scholars followed suit; Indians used Sri Lanka)

this became the standard for "westerliness" in Europe into well into the age of exploration, even after the discovery of the even farther west Azores and Cape Verde islands

astronomers tended use observatories as base zero for calculating ephemerides etc.

the alphonsine tables of 1252 used toledo as a baseline, the Rudofine tables used Ulm

Mercator#s prime meridian was through the cape verde islands on the theory that compasses there and in the azores pointed true north

But one one could pin down precisely where it was, as it happens, the socalled agonic meridian fluctuates and varies depending on Earth's magnetic field strength

globes between 1500 and 1700 use either the Canaries, the Cape Verdes or the Azores as their prime meridian, with little consistency over time.

In July 1634, King Louis XIII, under the direction of Cardinal Richliew of all people, re-established the authority of Ptolemy by declaring Ferro the prime meridian

this was largely symbolic, since the meridian had not been fixed

it had more to do with the diplomacy of the 30 years war (French ships were not to attack spanish or portuguese ships beyond that line)

In 1724, Louis Feuille travelled to Ferro to determine the prime meridian, the first geodetic mission to do so

He determined the paris-Ferro angular distance at 19 degrees 55 minutes, though 20 degrees was settled on

this work helped assert the Paris meridian as the Prime, and bolster nationalistic ego

The timings of occultations and eclipses (of the sun, moon, or preferably, moons of Jupiter, vary according to longitude, so a book of ephemerides could be used alongside a telescope to determine longitude at sea. Or a clock could be developed that kept accurate time at sea. Both were highly impractical

John Harrison worked on his marine chronometer for 43 years

tobias Meyer, a German astronomer, with his lunar tables was the runner up, and tested his almanacs against Harrison's sea clocks

among a fleet of east india merchant ships, perhaps fewer than ten people who could make a lunar observation

as Harrison's watch became more common, so did the Greenwich meridian among the British military and merchant navies

Maskyline's ephemeris was not immediately embraced by all of british sailors, particularly since many argued that your meridian is where you started from, meaning anything that relied on a single established meridian was pointless

Russia used all three meridians, paris, london, ferro, as well as its western edge, the iles of dego and osel in present day estonia

the spanish used paris, cadiz (site of the national observatory) and teneriffe

though the first map using the Greenwich meridian dates to 1738, though atlases using Ferro post date it

a sailor at sea didn't care for science or national pride; he used whatever he could

National meridians took decades to settle, 1750s in France; 1820s in the Low countries, 1780s in Britain

the first American books about American goegraphy used Philadelphia as the prime meridian

In 1804, thomas Jefferson established the white house as America's Prime Meridian.

Some argued that Greenwich was preferable, given the scientific debt America owed Britain, and also that it was unfair to the other inhabitants of the Americas

Others argued that too few observations had been done to accurately establish an American meridian, and since the meridian would have to be calibrated with Greenwich anyway, it seemed pointless.

the political need for a new meridian however, was potent.

As America grew westward, the idea of using Greenwich as the meridian became less practical.

Some suggested N Orleans, which is 90 degrees west of greenwich, as a possibility

marine merchants were unhappy with the idea, arguing that sailors in the US and UK had been using Greenwich perfectly and that 3/4ths of the commerce of the world relied on it

Some looked to the future and noted that soon there would only be one prime meridian, and that an American one would only slow its arrival

Others saw the idea of the world agreeing to a single meridian as wishful thinking

A compromised was reached: navigation would retain Greenwich as its meridian, but a separate meridian would be established at Washington for continental astronomy and geography

"there is no reason to think that one single first meridan can ever be established with the common consent of nations. All desire it, but how many will agree upon the choice?" Harvard professor

As global scientific standards merged, there grew a need not only for a shared metric system but for a shared common time

Otto Struve endorsed greenwich because most of the accurate scientific maps of the time used it as a meridian, and also Flamsteeds ephemerides were the most accurate

Greenwich's antimeridian was a barely inhabited region of the pacific, which made it a useful end time. Some suggested it would make a better prime meridian

Greenwch bisected Africa and Europe, unlike Ferro, still used in European schoolbooks at the time

Geography was not a settled science at that time

When trains used different timetables the results were catastrophic

1870 Charles Dowd divided America into four one hour time zones based on Greenwich

Even though greenwich mean time was established in 1675, different parts of england employed different local times

In 1840, the Great Western Railway established a common time throughout its network, based on GMT, and others followed, creating railway time

mean solar day vs actual time varies by as much as 15 minutes (earth's movement around the sun speed and axial tilt)

1883 IGA meeting: Adolphe Hirsch direcotr of Neuchatel Observatory in Switzerland and head of the international committee of weights and measures

universal time be that of the prime meridian; all days begin at zero and are called ante-meridian (AM) or post meridian (PM)

accuracy and practicality should be given precidence over political neutrality

1 oct 1884 International Meridian Conference Wash DC

Before it ended the conference would be attended by 40 delegates representing 25 countries

rome 1883: Grenwich was propsed, as it was the most likely to be accepted "virtually nil" that any other location would be adopted after rome Bartky

universal time would be counted from Greenwich midnight from 00:00 to 24:00. The universal day would not interfere with local time.

American delegate Lewis rutherfurd proposed a vote on a resolution declaring Greenwich the meridian, but the French delegates declared him "out of order" since they asserted they were not in thrall to Rome

to them, this was just a question of principle, though it was clearly far more than that

the french had asserted that geography offered two possibilities; the azores or the hering strait

others argued that the idea of a neutral meridian was a fiction, that it would ultimately be the meridian of whoever proposed it

the times expressed doubts that any agreement could be reached, and notetd that the Americans had described French behavior as puerile

many delegates agreed to adopt the greenwich meridian if the US and UK agreed to adopt the metric system.

tonnage statistics made Greenwich king

21 voted for, one against (santo domingo)

France and Brazil obstained

"mapmakers in general have long consented to use" Times

"The time has been mostly taken up with political diplomacy and sentiment" Science

Universal day, one direction only or two directions?

"the application of science to the means of locomotion and the instantaneous transmission of thought and speech have gradually contracted space and annihilated distance" Sandford flemning

the universal day would be a mean solar day

Japan adopted the Greenwich meridian for navigation but not time; France made no change at all

railways and telegraphy were already forcing the issue of universal time

greenwich was a slow but sure march; universal time much slower; decimalised time hardly at all

astronomical day (begins at midday) should conform with the civil day and begin at midnight

By 1898 14 different prime meridians were still in use

By 1916. most countries were on Greenwich mean time with greenwich as teh prime meridian. Even France begurugingly acquiesced in 1911.

On Batille day 2000, the French held a nationwide picnic on the Paris meridian

Teh Airy Transit circle was slightly off perpendicular, meaning that the Prime Meridian is now 102.5 metres west of its initial position

17th centuriy longiotude grijs

dutch golden age lat 17th centrury- john lock, thomas hobbes, czech protestant comenius

after the 80 years war, spanish ports were off limits to the dutch

but maps and charts were considered state secrets

christiaan huygens, levenhoek, renes descartes spent much iof his working life in the netherlands

Ptolemy chiose the isles of the blessed as his prime meridian

Hierro in the canaries (20 degrees west) no negative numbers

the timing of lunar eclipses was used by chinese to plot longitudes by the mongol dynasty

This was how amerigo vespucci calculated the longitude of the amazon river

rhumb lines lines crossing all lines of lattitude at the same angle- not the ame as a great circle, as they require changes in direction to follow

increases in trade and th discovery of the new world suddenly made determining longitude very important

Robert hooke investigated the possiblility of using a spring loaded clock to fidn longitude at sea, but the awards for doing so had dried up, and when he realised that anyone with a slightly different patent could claim royalties, he decided it wasn't worth it

Christiaan huygens ran successful tests of a seagoing pendulum clock in the relatively calm mediterranean, but doubts remained about it working in the open ocean

Jean richer cayenne pendulum clock debunked

Huygens attempted to turn to a spring powered watch, but found that springs are sentitive to temperature and humidity

1675: john flamsteed ecomes astronomer royal

forthwith to apply himself with the most exact care and dilligence to the rectifying of the tables of the motions of the heavens and the places of the fixed stars so as to find out the so much desired longitude of places for the perfecting of the art of navigation astronomer and mathematician jonas moore

No one knows who first coined the term astronomer royal; it's possible flamsteed simply assumed it himself.

Flamsteed used telescopic observations to correct the obsrevations of tycho brahe and the rudophine tables, the standard reference for the time

In 1667, upon hearing that the Paris Observatory was focusing on the longitude problem, mainly through the jovian method, Charles II decreed that England should have one too

two thomas tompion clocks that coudl go a full year on one winding

Flamsteed's first task was to prove that the earth rotated

2000 pounds of his own money met with promises, none came no equipment

this led to him being tardy in his publications, much to the chagrin of Halley and Newton, with whom relatiosn soon turned toxic

in 1712, halley went over flamsteed's head and published his results without his permission

in 1712 halley corrected flamsteeds observations, o=possibly just out of spite

he retained pure copies of his work as evidence of halley's misdeeds, but never saw them published

the final volume was published in 1725, six years after flamsteed's death

the results were precise enough to allow for lunar navigation

the errors introduced by his editors have tarnished flamsteeds reputation

1634: Louis xiii declared ferro the prime meridian, though its location is not precisely known

Harrison (gould)

Even simply delaying the time of arrival could be deadly, with scurvy still a problem

the simplest solution was for a ship to carry a clock telling the time at a fixed meridian

Another means was by lunar calculation. If the moon's motion can be known with sufficient accuracy, it is possible to measure its angular distance from specific stars or the Sun at various times, as viewed from a specific meridian, and then, with the aid of an almanac, calculate the difference aboard ship

using this method, James Cook was able to find his longitude to within 1 degree

However, once he had a chronometer, he switched to that

In 1714 the British parliament passed an act allowing for a longitude prize: 10,000 pounds if a method could be shown to work within a 60 mile error after six week voyage, 15 000 for 40 miles, 20 000 for 20 miles

it was the largest ever offered, and the only one that was ever paid

a rush of cranks soon flooded the committee, offering everything from sun dials to squaring the circle as a solution

the invention of the mainspring in the 16th century allowed for the creation of portable timepieces, but their terrible accuracy, losing up to half an hour per day, made them unsuitable for navigation.

Huygens had attempted to create a marine timekeeper, but a pendulum can only function if it is swung form a fixed motionless support, an impossibility at sea

very sophisticated attempts at calibration, sicj as mounmting on gymbals and linking two out of sych pendulums, ere made, but none could account for changes in temperature

Harrison was born in 1693 in Yorkshire the son ofa carpenter

Expected to folow in his father's tarde, he instead educated himself on the method for repair and construction of clocks, building his first when he was 21

he offered the committee two of his creations, a pendulum that was minimally affected by temperature, called the gridiron, and a near-frictionless escapement, called the grasshopper

before approaching the board, harrison went to halley (ar) at the royal observatory, who kindly informed him that the board would not advance him a shilling and that he'd be better off taking his plans to a respected clckmaker named geoge graham

graham advanced him enough money to fund the project (200 pounds?) and he got to work

he needed a complete clock to show the board

his first chronometer took him six years

it employed numerous attempts to minimize friction as well as the first ever compensation for changes in temperature

In 1736, harrison successfully tested his clock on a barge in the humber, and then took it before the board

the clock was tested at sea on a journey to Lisbon and found to be more accurate than dead reckoning.

the clock ran for 30 years continnuously withoput having to be oiled every friction point was either made of ioily wood or polished brass

in 1739, harrison created his number 2 a smaller, denser, more compact take on 1, but was never trialled at sea for fear of falling into enemy spanish hands

his third timekeeper took him seventeen years

he then informed the board that he wished to compete for the 20, but suggested the consturction of a watch to serve as a backup

To harrisons shock, the watch performed as wlel as number three, which he immediately shelved

In 1761, Harrison took his watch on trial on board the hms depford on a joruneyu to jamaica

After nine days out of sight of land, captain digges maintained by dead reckoning that the ship's longitude was 13.5 degrees west of london

the no 4 said it was 15.2 degrees west and that if he was correct, the islands of madeira, which they were aiming for, woulod be visible the next day. They did.

releived as they were "in want of beer"

Upon reaching jamaica, harrison's watch was found to be accurate to within 1 mile.

but the board played nasty and insisted on further trials, claiming that the longitude of jamaica was not known precisely enough. they were kind enough to advance him 2500 on account

the seocnd trial took place in 1764, to barbados with two observers, one of whom was nevil maskeline, soon to be astronomer royal

They were required to establish thier longitude from Barbados, and found the watch correct to within ten miles.

teh board still insisted, actuaklly reasonably, that he disclose uinder oath the consturction of his timepiece,and that he make two more to be tested by other hands. They still advanced him 7500

A seconnd watch was constructed by another watchmaker. Nevol maskelyne, who had a distaste both for timekeepers and Harrison, managed to conclude that the watch was not fit for purpose, despite the preceding ecvidence.

the duplicate went with James cook onm a journey from the trpics to the antarctic and cook had nothing but praise for it

But the aging harrison happened upon an ideal patorn, george III, who declared, "by god harrison I will see you righted"

Harrison still had to petition parliement, and, under threat of investigation, the board buckled and handed over the second half of his reward

but the board managed to bilk harrison of 1260 they demanded for the money they had granted him for the construction of his three timekeepers, which, despite the agreement specifying that the money was intended for the timekeepers themselves, whcih would be government property, they now called a loan. Harrison lost the money and the timekeepers

harrison was not a writer, he coudl do but not describe

harrison's watch had one crippling flaw, however, it was expensive, topping out at 450 a piece

but the land of the future industrial revolution was nothing if it couldn't mass produce cheap goods at scale, and soon new gernations fo clockmakers were finding ways to simplify the design

flamsteed

born of middle class parents in the north of england

plagued by chronic ill health

1669 sent an ephemeris to the preseidnet of the royual society, who put him i touch with jonas moore, who gave him a micrometer

richard townley had improved upon the first micrometers, and constructed a weatehr glass (barometer) which flamesteed, upon seeing it, constructed himself.

after attaining his MA at cambridge, where he met newton, he took orders

1674: Moore summoned flamsteed to london to head the royal observatory

A royal commission was set up to consider the feasiblity of the la sieur de saint pierre plan of sdeermining longitude by moon

Flamsteed was included and conmvinced the others that it was impracticable due to the impricision of both lunar timetabes and star catalogues

Christopher Wrens choice of Greenwich hill won out and construction began in 1675

flamesteeds catalogue comprised 3000 stars, and was accurate to within seconds of arc, compared to Tycho's minutes. (10 minutes prior to tycho)

300 stars added by Halley's trip to st helena