The Line That Serves as a Reference for Greenwich Mean Time

The prime meridian is a line of 0 degree longitude, the starting point for measuring distance both east and west around earth. It is erratic and can be chosen to be anywhere. In 1884, representatives from many countries came together to pick a standard meridian. The Greenwich Meridian became the international standard. 

Through how many countries do prime meridian pass through?

As per 2020, the Greenwich meridian or prime meridian passes through eight countries from north to south, the countries include-

1. United Kingdom
2. France
3. Algeria
4. Mail
5. Burkina Faso
6. Togo
7. Ghana
8. Antarctica

What is Greenwich Mean Time?

Greenwich Mean Time or GMT is the time displayed by the Shepherd Gate Clock at the Royal Observatory in Greenwich, London. When the sun is at its highest point exactly above Prime Meridian, it’s 12:00 noon at Greenwich. It is the reference point for every time zone in the world. Every 15 degree longitude represents one hour’s difference in time. GMT was originally set up to aid naval navigation when trade opened up. It is another word for Mean Solar time.

What is the Current Time? 

When it is exactly 4 pm in India time now at Greenwich is 10.30 am. There are 360 degrees in a full rotation which on earth is equal to 24 hours. Again 360 divided by 24 is 15, this is the reason why we add one hour for every time zone or 15 degrees longitude away from Greenwich, England to convert to local time. 

For example- There are a total of six time zones in the United States. The central time zone is in Wisconsin. The time zones of the US include- Eastern, Central, Mountain, Pacific, Alaska and Hawaii. Wisconsin is six hours behind the Prime Meridian time zone in the winter. 

Elucidate the History of Prime Meridian? 

This line has been called Prime Meridian or Greenwich Meridian since 1884, and it serves as the basis from which all terrestrial longitudes are measured and world’s time zones are calculated. A country in the East of Greenwich Meridian would be the time ahead of GMT. A country to the West of Greenwich Meridian shows time behind GMT.

 The daily rotation of the earth is irregular and gets slower. Atomic clocks thus constitute a stable timebase. On 1st January 1972, GMT was superseded by Coordinated Universal Time (UTC) maintained by several atomic clocks around the world. Historically GMT aid was used with two different conventions for numbering of hours. One is the long standing astronomical convention and the other is a civil convention. The term Greenwich Mean Time is still used to represent civil time in Britain. 

What is Universal Time Coordinated ?

The differences between the individual time zones are given in relation to Universal Time Coordinated, it is the time that exists on zero meridian and zero longitude. Germany is in time zone UTC+1. Greenwich Mean Time corresponds to time zone UTC 0, Coordinated World Time with an offset of 0 hours, corresponding to Western European time. 

The difference between GMT and UTC is that GMT is the name of the time zone, while UTC is a term for the time system that has its normal state on zero meridian. 

Timezone of UTC + 0 

The timezone is named Greenwich Mean Time, which means that the beginning and ending of daylight saving time always uniformly apply here. There are 4 counties in which the clock strikes just the same hour as these have the same distance to Universal Time Coordinated. Faroe Islands, Portugal, Sao Tome and Principe and Spain are in timezone of UTC + 0.

Write a note on the Greenwich of India? 

At present local time of India is calculated from a clock tower at Allahabad Observatory, at National Physical Laboratory in New Delhi. 

As per Hindu almanack it is always based on Ujjain time, 29 minutes behind IST. The Vedashala or Observatory is the best place to get a firsthand experience of Ujjain’s timekeeping techniques. The Tropic of Cancer is significant as the earth revolves around the sun, the latitude marks the northernmost position at which sun can be seen overhead directly. 

British India adopted the standard time zones in 1905, picking the meridian passing east of Allahabad at 82.5 degree east longitude as the central meridian for India. The single time zone for the country came into force on 1st January, 1906 applying to Sri Lanka too. 

Calcutta time remained a separate time zone till 1948. After independence in 1947, the Indian government established IST as the official time for the whole country, while Kolkata and Mumbai retained their own for a few more years. 

The country’s east west distance of more than 1200 miles covers 28 degrees of longitude resulting in change in sunrise and sunset timings. In 1980’s it was proposed to divide the country into two or three time zones to conserve energy. 

The Tropic of Cancer crosses Mahakal temple in Ujjain and Somnath temple in Gujarat. Thus time now in India will be the same for all states. It is also believed that this imaginary line passes through Ujjain’s temple of Mangalnath which is considered the birthplace of Mangal according to Hindu cosmology. The Surya Siddhanta provides the earliest descriptions of standard time in India. 

This observatory of India measures time, altitude, determines eclipses, and studies motions and orbits of planets. Shanku Yantra, Sampat yantra, Ganesha yantra, Nadi Valay yantra, Bhitti yantra and Taramandel are yantras or instruments that work on principle of casting shadows. 

There are five states in India through which Indian Standard Meridian, 82.5’E pass through, these are Uttar Pradesh, Madhya Pradesh, Chhattisgarh, Odisha and Andhra Pradesh. The total number of latitudes are 181 and total number of longitudes are 360. The Western most longitude is 180 W and the easternmost is 180 E. This is called the 180th meridian and also the international date line. 

Conclusion

The Meridian of 0 degrees longitude that runs through Greenwich of England is called the Prime Meridian or Greenwich Mean Time. Geographical grids are created that are imaginary, these grids are made of latitude, longitude, meridians or parallels. 

The geographical grid allows us to accurately describe locations on Earth in a universal way. Prime Meridian is similar to the equator that divides the earth into eastern and Western Hemisphere. Ujjain is India’s precise spot where Tropic of Cancer and zero meridian of longitude intersect.