IST Full Form and Meaning
The IST Full Form is Indian Standard Tim. It is used in India and Sri Lanka and was established in 1947 after India gained its independence. The IST is calculated from a clock tower in Mirzapur with directions 25.15 degrees North Latitude and 82.58 degrees East Longitude.
However, Kolkata and Mumbai adopted it only in 1948 and 1955, respectively.
GMT Full Form and Meaning
GMT stands for Greenwich Mean Time and was established in 1675. The Royal Observatory built it to assist the mariners in determining longitude at sea. It also helped them keep a standard reference time concerning other cities of England that used to keep different local times.
The Shepherd Gate Clock displays GMT Time at the Royal Observatory in Greenwich, London. When the sun is at its highest point above the Prime Meridian, it is noon at Greenwich. It is the reference point for every time zone in the world. Some GMT countries include the UK, Iceland, Greenland, and Ghana.
Difference Between IST and GMT
The Difference between GMTvs IST is discussed below in a tabular form.
Basis of Difference
Greenwich Mean Time (GMT)
Indian Standard Time (IST)
GMT was established in 1675 by the Royal Observatory to help navigators at sea.
IST was established in India in 1947 after India gained independence from British Rule.
GMT is considered equivalent to UTC (Universal Coordinated Time) for UK Civil purposes, but it is deemed equal to UT1 for navigation.
The Clock tower in Mirzapur is the basis of the calculation of IST. The tower coordinates are- 25.15 degrees North Latitude and 82.58 degrees East longitude.
GMT calculates time-based on Sun. However, because of the earth's uneven angular velocity and tilt in its axis, noon GMT may not be the exact time when the sun reaches the highest point in the sky.
The Time and Frequency Standards Laboratory at the National Physical Laboratory in New Delhi generates the official time signal for IST.
The signals are based on atomic clocks that are synchronized with UTC.
Replacement and Sufficiency
GMT was replaced by UTC as the international time standard in 1972. UTC is based on atomic measurements and hence is more accurate.
Demand for separating India into different time zones has been raised time and again. A time zone differentiated by one hour has been requested for Northeastern regions.
Countries that follow the time zone
GMT is used in the UK and other commonwealth nations such as Australia, New Zealand, and the countries of the Eastern Hemisphere.
IST is used in India and Sri Lanka.
UT1 is the modern form of mean solar time at 0 degrees longitude. UTC and UT1 differ by up to 0.9 seconds.
>> Difference Between GMT and IST [PDF]
GMT or Greenwich Mean Time is the time measured on Earth's 0-degree longitude which passes through Old Royal Observatory near London. India is +5:30 hours ahead of the GMT time.
The GMT is now known as the Universal Coordinated Time (UTC).
Difference Between GMT and IST Questions
Question: Every country calculates its Standard meridian as the angular distance from the Greenwich meridian. If it is12 noon at GMT, what is the time on Indian Standard Time?
- 5:30 P.M
- 5:00 P.M
- 5:20 P.M
- 5:30 A.M
Answer: Option A