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How to use gmt in a sentence?

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Answer # 1 #

The Royal Observatory Greenwich is the home of Greenwich Mean Time (GMT). But what is GMT and why is it so important?

Greenwich Mean Time is the yearly average (or ‘mean’) of the time each day when the Sun crosses the Prime Meridian at the Royal Observatory Greenwich.

Essentially, mean time is clock time rather than solar (astronomical) time.

Solar time varies throughout the year, as the time interval between the Sun crossing a set meridian line changes.

But each day measured by a clock has the same length, equal to the average (mean) length of a solar day. It’s a way of standardising and regularising time so we can all know exactly what time it is for our (or anyone’s) location.

Today GMT is reckoned from one midnight to the next.

Find out about the Prime Meridian

GMT stands for Greenwich Mean Time, the local clock time at Greenwich. From 1884 until 1972, GMT was the international standard of civil time. Though it has now been replaced by Coordinated Universal Time (UTC), GMT is still the legal time in Britain in the winter, used by the Met Office, Royal Navy and BBC World Service. Greenwich Mean Time is also the name of the time zone used by some countries in Africa and Western Europe, including in Iceland all year round.

It wasn’t until the invention of the pendulum clock in the 1650s that it was possible to work out the relationship between mean (clock) time and solar time.

John Flamsteed came up with the formula for converting solar time to mean time, and published a set of conversion tables in the early 1670s. Soon after, he was appointed as the first Astronomer Royal and moved into the new Royal Observatory in Greenwich.

Here he had the best pendulum clocks installed and set them to the local time. This was Greenwich Mean Time, or the average time when the Sun crossed the meridian at Greenwich. At first though, Greenwich time was only really important to astronomers.

In the 1700s, the fifth Astronomer Royal Nevil Maskelyne brought Greenwich Mean Time to a wider audience.

In 1767 Maskelyne introduced the Nautical Almanac as part of the great 18th century quest to determine longitude.

These were tables of ‘lunar distance’ data based on observations at Greenwich and using GMT as the time standard. This data enabled navigators to find their position at sea.

GMT was also crucial to the other great solution to the ‘longitude problem’, represented by John Harrison’s famous timekeepers.

British mariners started keeping at least one chronometer set to GMT. This meant they could calculate their longitude from the Greenwich meridian (longitude 0° by convention).

These two solutions would help pave the way for GMT to become the worldwide time standard a century later.

Find out about the longitude problem

Until the mid-19th century, almost every town kept its own local time, defined by the Sun. There were no national or international conventions which set how time should be measured.

This meant there was no standard timings for when the day would begin and end, or what length an hour might be. As well as Greenwich Mean Time for example, there was also Bristol Mean Time (10 minutes behind GMT) Cardiff Mean Time (13 minutes behind GMT).

However, the 1850s and 1860s saw the expansion of the railway and communications networks. This meant the need for an national time standard became imperative.

British railway companies started introducing a single standard time across their networks, designed to make their timetables less confusing. It was mostly Greenwich Mean Time that they used. GMT was ultimately adopted across Great Britain by the Railway Clearing House in December 1847. It officially became 'Railway Time'.

By the mid-1850s, almost all public clocks in Britain were set to Greenwich Mean Time and it finally became Britain’s legal standard time in 1880.

In 1884 the Greenwich Meridian was recommended as the Prime Meridian of the World.

There were two main reasons for this. The first was that the USA had already chosen Greenwich as the basis for its own national time zone system. The second was that in the late 19th century, 72% of the world's commerce depended on sea-charts which used Greenwich as the Prime Meridian.

The recommendation was based on the argument that naming Greenwich as Longitude 0º would be of advantage to the largest number of people.

As the reference for GMT, the Prime Meridian at Greenwich therefore became the centre of world time and the basis for the global system of time zones.

The Airy Transit Circle (telescope) became the telescope that would define the Prime Meridian of the World. Astronomer Royal George Biddell Airy designed it, and it is located at the Royal Observatory Greenwich.

It was recommended that the meridian line would indicate 0° longitude. Therefore this also became the start of the Universal Day. The meridian line is marked by the cross-hairs in the Airy Transit Circle eyepiece.

Find out more about the Airy Transit Circle

The Shepherd gate clock can be seen at the gates to the Royal Observatory. It was the first clock ever to show Greenwich Mean Time directly to the public. It is a 'slave' clock, connected to the Shepherd master clock which was installed at the Royal Observatory in 1852.

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Jordan Mihashi
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Answer # 2 #

The Royal Observatory Greenwich is the home of Greenwich Mean Time (GMT). But what is GMT and why is it so important?

Greenwich Mean Time is the yearly average (or ‘mean’) of the time each day when the Sun crosses the Prime Meridian at the Royal Observatory Greenwich.

Essentially, mean time is clock time rather than solar (astronomical) time.

Solar time varies throughout the year, as the time interval between the Sun crossing a set meridian line changes.

But each day measured by a clock has the same length, equal to the average (mean) length of a solar day. It’s a way of standardising and regularising time so we can all know exactly what time it is for our (or anyone’s) location.

Today GMT is reckoned from one midnight to the next.

Find out about the Prime Meridian

GMT stands for Greenwich Mean Time, the local clock time at Greenwich. From 1884 until 1972, GMT was the international standard of civil time. Though it has now been replaced by Coordinated Universal Time (UTC), GMT is still the legal time in Britain in the winter, used by the Met Office, Royal Navy and BBC World Service. Greenwich Mean Time is also the name of the time zone used by some countries in Africa and Western Europe, including in Iceland all year round.

It wasn’t until the invention of the pendulum clock in the 1650s that it was possible to work out the relationship between mean (clock) time and solar time.

John Flamsteed came up with the formula for converting solar time to mean time, and published a set of conversion tables in the early 1670s. Soon after, he was appointed as the first Astronomer Royal and moved into the new Royal Observatory in Greenwich.

Here he had the best pendulum clocks installed and set them to the local time. This was Greenwich Mean Time, or the average time when the Sun crossed the meridian at Greenwich. At first though, Greenwich time was only really important to astronomers.

In the 1700s, the fifth Astronomer Royal Nevil Maskelyne brought Greenwich Mean Time to a wider audience.

In 1767 Maskelyne introduced the Nautical Almanac as part of the great 18th century quest to determine longitude.

These were tables of ‘lunar distance’ data based on observations at Greenwich and using GMT as the time standard. This data enabled navigators to find their position at sea.

GMT was also crucial to the other great solution to the ‘longitude problem’, represented by John Harrison’s famous timekeepers.

British mariners started keeping at least one chronometer set to GMT. This meant they could calculate their longitude from the Greenwich meridian (longitude 0° by convention).

These two solutions would help pave the way for GMT to become the worldwide time standard a century later.

Find out about the longitude problem

Until the mid-19th century, almost every town kept its own local time, defined by the Sun. There were no national or international conventions which set how time should be measured.

This meant there was no standard timings for when the day would begin and end, or what length an hour might be. As well as Greenwich Mean Time for example, there was also Bristol Mean Time (10 minutes behind GMT) Cardiff Mean Time (13 minutes behind GMT).

However, the 1850s and 1860s saw the expansion of the railway and communications networks. This meant the need for an national time standard became imperative.

British railway companies started introducing a single standard time across their networks, designed to make their timetables less confusing. It was mostly Greenwich Mean Time that they used. GMT was ultimately adopted across Great Britain by the Railway Clearing House in December 1847. It officially became 'Railway Time'.

By the mid-1850s, almost all public clocks in Britain were set to Greenwich Mean Time and it finally became Britain’s legal standard time in 1880.

In 1884 the Greenwich Meridian was recommended as the Prime Meridian of the World.

There were two main reasons for this. The first was that the USA had already chosen Greenwich as the basis for its own national time zone system. The second was that in the late 19th century, 72% of the world's commerce depended on sea-charts which used Greenwich as the Prime Meridian.

The recommendation was based on the argument that naming Greenwich as Longitude 0º would be of advantage to the largest number of people.

As the reference for GMT, the Prime Meridian at Greenwich therefore became the centre of world time and the basis for the global system of time zones.

The Airy Transit Circle (telescope) became the telescope that would define the Prime Meridian of the World. Astronomer Royal George Biddell Airy designed it, and it is located at the Royal Observatory Greenwich.

It was recommended that the meridian line would indicate 0° longitude. Therefore this also became the start of the Universal Day. The meridian line is marked by the cross-hairs in the Airy Transit Circle eyepiece.

Find out more about the Airy Transit Circle

The Shepherd gate clock can be seen at the gates to the Royal Observatory. It was the first clock ever to show Greenwich Mean Time directly to the public. It is a 'slave' clock, connected to the Shepherd master clock which was installed at the Royal Observatory in 1852.

From that time until 1893, the Shepherd master clock was the heart of Britain's time system. Its time was sent by telegraph wires to London, Edinburgh, Glasgow, Dublin, Belfast and many other cities. By 1866, time signals were also sent from the clock to Harvard University in Cambridge, Massachusetts via the new transatlantic submarine cable.

In terms of the distribution of accurate time into everyday life, it is one of the most important clocks ever made.

The first thing you notice about the clock is that it has 24 hours on its face rather than the usual 12. That means at 12 noon the hour hand is pointing straight down rather than straight up.

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Asad Tendulkar
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Answer # 3 #

Always specify the time zone when not specifying one would cause confusion. If the reader of your report, article, or other document is not local to a single time zone, specify the time zone for all clock times mentioned. Similarly, if the times mentioned span different time zones, make sure to clearly indicate which zone you’re referring to.

However, if you and your readers are in the same time zone (for example, within the same physical office), or if the time zone is immaterial (like in a piece of creative writing), it is unnecessary information and should be omitted.

When indicated alongside a clock time, time zones are usually abbreviated. But when a clock reading isn’t mentioned, they are spelled out.

When it is clear which time zone is being referred to, abbreviations are usually sufficient, especially within a national context. But note that these abbreviations are not internationally standardized and can cause confusion: for example, PST is both Pacific Standard Time and Philippine Standard Time. Similarly, IST can be Indian Standard Time, Irish Standard Time, or Israel Standard Time. If there is any chance your audience could be confused, spell out the time zone instead of using an abbreviation.

When spelled out, time zones may be either capitalized or lowercased. Style manuals differ in their recommendations: The Chicago Manual of Style, followed in U.S. book publishing, recommends lowercasing them. In contrast, the AP Stylebook suggests capitalizing the full forms of time zones. Choose a style and follow it consistently across a document.

Don’t insert periods after the letters of a time zone. Abbreviations with all capital letters generally don’t contain internal punctuation.

Don’t enclose the abbreviation for a time zone in commas. However, if you spell out a time zone accompanied by a clock time, enclose it in commas.

Of course, if the time zone appears in running text without an accompanying clock reading, don’t unnecessarily set it off with commas.

In running text, time zones may be enclosed in parentheses (or round brackets). This is optional: the Chicago Manual of Style recommends using parentheses; the AP Stylebook suggests omitting them.

Many regions and territories of the world set clocks forward and back in summer and winter. The letter D in a time-zone abbreviation usually indicates that the time zone is in daylight saving time (DST).

Coordinated Universal Time (UTC), the primary global time standard, indicates the same time as GMT but has now superseded GMT in international use. In many international publications, particularly academic and scientific, UTC offsets are preferred over references to local time zones (EST, PST, etc.). Since abbreviations of time zones are not standardized across the globe, they can be confusing to an international audience. A UTC offset is shown as plus (+) or minus (-) the number of hours and minutes it is ahead of or behind UTC.

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