This article is from the source 'guardian' and was first published or seen on . It last changed over 40 days ago and won't be checked again for changes.
You can find the current article at its original source at http://www.theguardian.com/science/the-h-word/2014/mar/30/farewell-greenwich-mean-time-history-science
The article has changed 3 times. There is an RSS feed of changes available.
| Version 0 | Version 1 |
|---|---|
| Farewell Greenwich Mean Time (see you in October) | Farewell Greenwich Mean Time (see you in October) |
| (about 14 hours later) | |
| It has become something | It has become something |
| of a tradition | of a tradition |
| on this blog to mark the biannual change of the clocks and, although I no | on this blog to mark the biannual change of the clocks and, although I no |
| longer work at the Royal | longer work at the Royal |
| Observatory Greenwich, it’s a habit that sticks. This time, as we say | Observatory Greenwich, it’s a habit that sticks. This time, as we say |
| farewell to it until the autumn, it seems a good opportunity to reminisce about | farewell to it until the autumn, it seems a good opportunity to reminisce about |
| Greenwich Mean Time.* | Greenwich Mean Time.* |
| Why Greenwich time? And what’s mean about it? | Why Greenwich time? And what’s mean about it? |
| Mean time is clock time. It is a | Mean time is clock time. It is a |
| regularised, idealised version of solar time that is tracked not by the | regularised, idealised version of solar time that is tracked not by the |
| apparent motions of the Sun, observed by shadows on sundials, but by a | apparent motions of the Sun, observed by shadows on sundials, but by a |
| mechanical device that splits the solar day into equal parts. Mean time ticks | mechanical device that splits the solar day into equal parts. Mean time ticks |
| away at the same pace no matter the season. The difference between the two is | away at the same pace no matter the season. The difference between the two is |
| described by the equation | described by the equation |
| of time. | of time. |
| Establishing the relationship between mean | Establishing the relationship between mean |
| solar time and apparent solar time only really became possible, or useful, with | solar time and apparent solar time only really became possible, or useful, with |
| the arrival of the pendulum clock in the 1650s. This made the mechanical clock, | the arrival of the pendulum clock in the 1650s. This made the mechanical clock, |
| for the first time, a scientific instrument. Christiaan Huygens, who developed | for the first time, a scientific instrument. Christiaan Huygens, who developed |
| the first prototype | the first prototype |
| pendulum clock in 1656, was able to produce reasonably accurate tables of | pendulum clock in 1656, was able to produce reasonably accurate tables of |
| the equation of time in 1665. | the equation of time in 1665. |
| However, it fell to John Flamsteed to publish | However, it fell to John Flamsteed to publish |
| tables in 1672-3 that tackled the problem in what became the standard way. He | tables in 1672-3 that tackled the problem in what became the standard way. He |
| provided the formula by which apparent solar time could be converted into Mean | provided the formula by which apparent solar time could be converted into Mean |
| Time. | Time. |
| Just a couple of years later, Flamsteed was | Just a couple of years later, Flamsteed was |
| appointed the first Astronomer Royal and moved into the newly built observatory | appointed the first Astronomer Royal and moved into the newly built observatory |
| in Greenwich. There, he and his patrons had installed state-of-the-art pendulum | in Greenwich. There, he and his patrons had installed state-of-the-art pendulum |
| clocks by the best clockmaker available, Thomas Tompion. With | clocks by the best clockmaker available, Thomas Tompion. With |
| observations of the Sun and the help of his tables, Flamsteed set these clocks | observations of the Sun and the help of his tables, Flamsteed set these clocks |
| to the local time: Greenwich Mean Time. | to the local time: Greenwich Mean Time. |
| Greenwich time became important because | Greenwich time became important because |
| there were people measuring it and because other people made use of | there were people measuring it and because other people made use of |
| astronomical observations based on it. Flamsteed’s catalogue of stars, which | astronomical observations based on it. Flamsteed’s catalogue of stars, which |
| was to become a standard reference work for the following decades, listed their | was to become a standard reference work for the following decades, listed their |
| positions based on Greenwich time. | positions based on Greenwich time. |
| It was one of Flamsteed’s successors, Nevil Maskelyne, | It was one of Flamsteed’s successors, Nevil Maskelyne, |
| Astronomer Royal from 1765 to 1811, who did most to ensure that GMT mattered to | Astronomer Royal from 1765 to 1811, who did most to ensure that GMT mattered to |
| more than just astronomers. Under his initiative, observations made at | more than just astronomers. Under his initiative, observations made at |
| Greenwich were processed into tables that could be used by navigators and | Greenwich were processed into tables that could be used by navigators and |
| cartographers to establish positions at sea or on land. This was the Nautical Almanac, | cartographers to establish positions at sea or on land. This was the Nautical Almanac, |
| first published for the year 1767. | first published for the year 1767. |
| Surveyors of the Royal Navy and the | Surveyors of the Royal Navy and the |
| Ordnance Survey relied on data that was based on observations made at Greenwich, | Ordnance Survey relied on data that was based on observations made at Greenwich, |
| meaning that their charts and maps used Greenwich as a reference point. More | meaning that their charts and maps used Greenwich as a reference point. More |
| precisely, this was the meridian (north-south line) on which the chief | precisely, this was the meridian (north-south line) on which the chief |
| telescope at Greenwich was mounted. The Greenwich meridian thus became a | telescope at Greenwich was mounted. The Greenwich meridian thus became a |
| prime meridian for British mapping, and east-west position was measured from | prime meridian for British mapping, and east-west position was measured from |
| there. To establish longitudes it was necessary to know the difference between | there. To establish longitudes it was necessary to know the difference between |
| local time and GMT. This could be worked out with astronomical observations and | local time and GMT. This could be worked out with astronomical observations and |
| the tables of the Nautical Almanac and, increasingly, with chronometers set to | the tables of the Nautical Almanac and, increasingly, with chronometers set to |
| GMT. | GMT. |
| The move of GMT from the specialist worlds | The move of GMT from the specialist worlds |
| of astronomy, navigation and surveying into civilian life was down to the | of astronomy, navigation and surveying into civilian life was down to the |
| increasing role of technologies and cultures that demanded standardization. The | increasing role of technologies and cultures that demanded standardization. The |
| arrival of railways made timetabling a necessity. Telegraph systems made it | arrival of railways made timetabling a necessity. Telegraph systems made it |
| both desirable and possible to know what time it was elsewhere. Factory work | both desirable and possible to know what time it was elsewhere. Factory work |
| made production and payment dependent on timekeeping. | made production and payment dependent on timekeeping. |
| GMT became “Railway Time” in the 1840s, | GMT became “Railway Time” in the 1840s, |
| and Britain’s legal standard time in 1880. Despite what you’ll often read, it | and Britain’s legal standard time in 1880. Despite what you’ll often read, it |
| did not become an international standard in 1884. In that year an | did not become an international standard in 1884. In that year an |
| international conference did recommend the adoption of the Greenwich meridian | international conference did recommend the adoption of the Greenwich meridian |
| as the world’s reference point for time and longitude, but it was just a | as the world’s reference point for time and longitude, but it was just a |
| recommendation. | recommendation. |
| What actually happened as a result of the | What actually happened as a result of the |
| International Meridian Conference, and what did not, is a story for another | International Meridian Conference, and what did not, is a story for another |
| post. See you back here on 26 October. | post. See you back here on 26 October. |
| * Our standard time is now in fact Coordinated Universal Time (UTC), derived from International Atomic Time but as close as darn it to GMT. | * Our standard time is now in fact Coordinated Universal Time (UTC), derived from International Atomic Time but as close as darn it to GMT. |
| Rebekah | Rebekah |
| Higgitt is one of the curators of Ships, | Higgitt is one of the curators of Ships, |
| Clocks and Stars: the Quest for Longitude (11 July 2014-4 January 2015), a | |
| forthcoming exhibition at the National Maritime Museum marking the tercentenary | forthcoming exhibition at the National Maritime Museum marking the tercentenary |
| of the first Longitude Act, and which includes the story of the Nautical | of the first Longitude Act, and which includes the story of the Nautical |
| Almanac and the development of marine timekeepers. | Almanac and the development of marine timekeepers. |