Local and Standard Time

Local And Standard Time and the International Date Line – UPSC Geography Notes

Table of Contents

Local time refers to the time standard followed in a specific region or locality, often determined by the position of the sun in the sky. It can vary from one location to another, leading to a range of time zones worldwide. In contrast, Standard Time is a uniform timekeeping system established for broader regions or countries, designed to create consistency within a defined area, usually corresponding to a time zone. On the other hand, the International Date Line is an imaginary line that runs north to south in the Pacific Ocean, roughly along the 180th meridian. Crossing this line signifies a change in calendar date, with the day advancing by one when moving west across the line and regressing by one when moving east, contributing to the complexities of global timekeeping and date tracking.

Local Time

  • Local time is determined by the sun’s position in the sky over a particular place.
  • All locations on the same meridian experience noon simultaneously.
  • The Earth’s 360º rotation in 24 hours equates to a 15º shift per hour and a 4-minute time difference per 1º of longitude.
  • Places to the east of a reference point experience earlier sunlight, leading to advanced time, while places to the west witness it later, causing a time lag.
  • For instance, if it’s noon at the Greenwich or 0º meridian, it would be 12:04 pm at 1º E and 11:56 am at 1º W.
  • This results in a diversity of local times across countries, with wider east-west spans amplifying the discrepancies.

Standard Time

  • Standard time denotes the local time used in a region or country when Daylight Saving Time (DST) is not in practice.
  • It is often termed winter time or normal time, while DST is also known as summer time, particularly in the UK.
  • Over 60% of countries worldwide employ standard time year-round, while the remaining nations implement DST during summer, adjusting clocks forward by an hour from standard time.
  • Standard Time was established in the late 19th century to resolve the confusion arising from the use of various local solar times within different communities, a predicament amplified by the rise of railway transportation.
  • Sir Sandford Fleming, a Canadian railway planner, proposed a global standard time plan in the 1870s, leading to the adoption of a system akin to the present one during a 1884 international conference in Washington, D.C.
  • The current system relies on 24 standard meridians of longitude, each 15° apart, with the prime meridian through Greenwich, England, acting as the reference point.
  • While theoretically each standard meridian corresponds to a time zone, in practice, these zones are often subdivided or modified for convenience.
  • Notably, some regions maintain time differences of half-hour or quarter-hour increments from the standard time.
  • Additionally, Daylight Saving Time is a common practice implemented to extend daylight hours during conventional waking times, typically observed during a part of the year, especially in summer.

Indian Standard Time

  • Indian Standard Time (IST) is the time standard observed across India, with a time offset of UTC+5:30. India generally does not adhere to daylight saving time (DST) or other seasonal adjustments, although it briefly adopted DST during the Sino-Indian War of 1962 and the Indo-Pakistani Wars of 1965 and 1971.
  • In military and aviation time, IST is denoted as E* (“Echo-Star”).
  • Indian Standard Time is anchored on the basis of 82.5° E longitude, located just west of Mirzapur, near Allahabad in the state of Uttar Pradesh.
  • The time variance between Mirzapur and the United Kingdom’s Royal Observatory at Greenwich translates to an exact time difference of 5 hours and 30 minutes.
  • While a clock tower at the Allahabad Observatory (15° N 82.5° E) computes local time, the National Physical Laboratory in New Delhi is responsible for maintaining the official time-keeping devices.
Indian Standard Time

History of Indian Standard Time

  • Until the mid-19th century, most towns in India adhered to their local time, but with the advent of railways, the necessity for a unified time zone became apparent.
  • Mumbai (formerly Bombay) and Kolkata (formerly Calcutta), serving as headquarters of the two largest Presidencies of British India, played a pivotal role in the adoption of a standardized time system by neighboring provinces and princely states.
  • In the 19th century, the introduction of the telegraph facilitated clock synchronization, with the railways using a time signal from the head or regional offices daily to synchronize their clocks.
  • The International Meridian Conference in 1884, held in Washington, D.C., established uniform time zones worldwide, assigning two time zones to India, with Calcutta utilizing the 90th east meridian and Bombay the 75° E meridian.
  • The conference designated Calcutta time as 5 hours, 30 minutes, and 21 seconds ahead of GMT, and Bombay time as 4 hours and 51 minutes ahead.
  • By the late 1880s, several railway companies adopted “Madras time” (also known as “Railway time”) as an interim standard between the two main zones.
  • The British colonial government instituted another time zone, Port Blair mean time, based in Port Blair, the capital of the Andaman and Nicobar Islands, setting it 49 minutes and 51 seconds ahead of Madras time.
  • British India formally adopted standard time zones in 1905, selecting the 82.5° E meridian passing east of Allahabad as the central meridian for the country, which came into effect on January 1, 1906, also encompassing Sri Lanka (then Ceylon). Calcutta time persisted as an official, distinct time zone until 1948.
Indian Standard Time

Indian Standard Time in relation with the bordering nations

  • Starting in 1925, the government initiated the transmission of time synchronization through omnibus telephone systems and control circuits to organizations requiring precise time information. This practice continued until the 1940s when the government transitioned to broadcasting time signals via radio.
  • Following India’s independence in 1947, the government established Indian Standard Time (IST) as the official time for the entire country, although Kolkata and Mumbai maintained their local time for a few additional years.
  • The Central observatory was relocated from Chennai to a spot near Mirzapur, situated as closely as possible to UTC +5:30.
  • During the Sino-Indian War of 1962 and the Indo-Pakistani Wars of 1965 and 1971, the government briefly implemented daylight saving time to reduce civilian energy consumption.

Issues with Indian Standard Time

  • Spanning over 2,000 km (1,200 miles) from east to west, India covers more than 28 degrees of longitude, leading to the sun rising and setting about two hours earlier in the north-eastern Seven Sister States than in the far-western Rann of Kutch.
  • In the late 1980s, a group of researchers proposed dividing the country into two or three time zones to conserve energy. They suggested a binary system resembling the British-era time zones, which the government ultimately dismissed.
  • In 2001, the government formed a four-member committee under the Ministry of Science and Technology to assess the necessity of multiple time zones and daylight saving. The committee’s recommendations, presented to Parliament in 2004 by the then Minister for Science and Technology, Kapil Sibal, advised maintaining the existing unified system. They emphasized that the choice of the prime meridian was centered around a particular station, and India’s expanse did not warrant multiple time zones.
  • Although the government has consistently rejected the idea of implementing multiple time zones, provisions in labor laws, such as the Plantations Labour Act, 1951, empower the Central and State governments to define and establish the local time for specific industrial areas.
  • An article published in the August 2007 edition of the Current Science journal projected that advancing Indian Standard Time six hours ahead of Universal Coordinated Time, instead of the current 5.5 hours, could potentially reduce evening peak energy demand by up to 16 percent. The authors estimated the resulting annual savings to be approximately Rs 1,000 crore.

Time Signals

  • The Time and Frequency Standards Laboratory at the National Physical Laboratory in New Delhi generates official time signals for commercial and official use.
  • It relies on atomic clocks that synchronize with the global system of clocks supporting the Coordinated Universal Time.
  • Features of the laboratory include four caesium and rubidium atomic clocks.
  • It operates a high-frequency broadcast service at 10 MHz under the call sign ATA, ensuring clock synchronization within a millisecond.
  • The Indian National Satellite System provides a satellite-based standard time and frequency broadcast service, offering Indian Standard Time accurate to ±10 microseconds and frequency calibration up to ±10−10.
  • Time and frequency calibrations are conducted using pico- and nanosecond time interval frequency counters and phase recorders.
  • The All India Radio and Doordarshan television network broadcast the exact time.
  • Telephone companies provide dedicated phone numbers connected to mirror time servers, relaying precise time information.
  • Global Positioning System (GPS) receivers are increasingly used for obtaining accurate time data.

Daylight Saving Time

Daylight Saving Time, also known as summer time, is a practice where clocks are uniformly adjusted forward to extend daylight hours during conventional waking time in the summer months. In countries situated in the Northern Hemisphere, clocks are typically advanced by one hour in late March or April and then set back by one hour in late September or October.

About Daylight Saving Time

  • The concept was initially proposed in a playful essay by Benjamin Franklin in 1784.
  • During World War I, several countries, including Australia, Great Britain, Germany, and the United States, adopted summer Daylight Saving Time to conserve fuel by reducing the need for artificial light.
  • Approximately 70 countries, including those in the European Union, practice DST.
  • India does not adhere to daylight saving time due to the minimal variations in daytime hours near the Equator. However, there is an ongoing discussion about the rationale behind maintaining a single time zone in a geographically vast country like India.
  • In the United States, DST is observed throughout the country, except in Hawaii and most of Arizona. In Australia, DST is practiced in New South Wales, Victoria, South Australia, and Tasmania, among other smaller territories, while it is not observed in Queensland and Western Australia, among other territories.

Objectives for using Daylight Saving Time

  • Promote energy efficiency: With a heightened emphasis on energy conservation driven by climate change concerns resulting from excessive energy consumption, DST gains significance. Hence, DST represents an environmentally sustainable concept.
  • Extend evening daylight: DST aims to shift the clock to display a delayed sunrise and a delayed sunset, effectively elongating the period of daylight in the evening.
  • Advance completion of tasks: By moving the clock forward, routine activities can be completed an hour earlier, aligning with the shifted daylight hours.
  • Energy-saving purpose: DST is primarily designed to conserve energy.

Daylight Saving Time role in economy of an area

Possible Positive role

On energy consumption
  • The energy sector significantly influences the economy, generating employment opportunities and value while permeating various segments of the economy, thereby fostering economic expansion. Daylight saving time is believed to have an impact on energy consumption.
  • According to a report submitted to Congress by the U.S. Department of Energy, extending daylight saving time by four weeks resulted in a daily saving of approximately 0.5% of the nation’s electricity consumption.
On Retail
  • The primary beneficiaries of DST include retailers, sporting goods manufacturers, and other businesses that capitalize on additional afternoon daylight.
  • The extended period of sunlight between the typical end of the workday and bedtime encourages customers to engage in shopping activities and participate in outdoor sports during the late afternoon.
  • In 1984, Fortune magazine approximated that prolonging DST by seven weeks would result in an added $30 million in revenue for 7-Eleven stores.
On leisure sector
  • The National Golf Foundation approximated that this extension would lead to a rise in golf industry earnings by $200 million to $300 million.
  • According to a study conducted in 1999, it was projected that DST contributes to an increase in revenue for the leisure sector of the European Union by approximately 3%.
On human capital
  • It is well-established that an enhanced state of health could potentially add $12 trillion to the global GDP by 2040. Daylight saving time (DST) can play a significant role in this regard, as proponents of DST highlight the advantages of extended evening hours in promoting healthier lifestyles and fostering a healthier society.
Increased safety
  • Decreased evening activities in the dark lead to reduced crime rates and traffic accidents.

Possible negative role

On Agriculture sector
  • Some farmers and individuals whose schedules are regulated by sunlight can be adversely affected by DST. One reason for farmers’ resistance to DST is that the optimal time for harvesting grains is after the evaporation of dew.
  • Consequently, the early arrival and departure of field hands in the summer diminish the value of their labor. Dairy farmers also face challenges due to DST as their cows’ milking schedules are sensitive to timing, causing disruptions when milk is delivered earlier.
On energy consumption
  • Critics of DST point out that advancements in lighting technology have led to reduced energy consumption from lighting compared to previous decades.
  • Heating and cooling are considered more significant contributors to energy consumption compared to lighting.
  • Some regions may require increased air-conditioning usage to cope with the longer and hotter evenings during daylight saving time.
Loss of workdays due to injuries
  • An examination of mining injuries across the U.S. indicated a significant surge of almost 6 percent in workplace injuries on the Monday following the transition to daylight saving time.
  • Moreover, the severity of these injuries, measured by the number of workdays lost, escalated by a striking 67 percent. This increase translated to an additional 2,600 workdays lost due to injuries experienced on that specific day.
On labour and work productivity
  • The week following DST witnesses a significant decline in workplace productivity as individuals experience fatigue and lethargy due to reduced sleep.
  • Typically, there is a slight downturn in stock market performance following the time change.
  • Regarding human health and its impact on human capital:
    • DST elevates the risk of heart attacks by 25%, while reverting to the original times reduces the risk by 21%.
    • Disrupted sleep patterns can potentially affect memory, learning, social interactions, and overall cognitive performance.
  • Various health issues arise as a consequence of the disturbance to the body’s circadian rhythm (body clock).
On accidents
  • According to one study, the loss of one hour of sleep in the US results in an estimated 5.4% to 7.6% increase in the fatal crash rate for six consecutive days following the transition.

International Date Line

International Date Line
  • The International Date Line (IDL) serves as an imaginary boundary stretching from the North to the South Pole, effectively separating two consecutive calendar days.
  • It holds significant importance in time measurement and plays a critical role in facilitating instantaneous communication, political coordination, and international trade.
  • The IDL closely approximates the 180° line of longitude, primarily traversing through the expanse of the Pacific Ocean.
  • Despite its conceptual straight path, the line meanders in certain regions, creating a zig-zag shape that occasionally veers east or west of the 180° meridian.
  • These variations allow areas with shared economic and political affiliations to adhere to the same date or time designation.
  • Beginning from the North Pole, the IDL initially veers eastward, passing close to the Chukchi Peninsula and Wrangel Island, then traverses through the Bering Strait before bending westward near St. Matthew and St. Lawrence Islands.
  • Between the Commander Islands and the Aleutian Islands, the line returns to the 180° meridian, continues until it crosses the equator, and then swings significantly eastward near the 150° meridian, encompassing Kiribati.
  • Subsequently, it shifts westward, consistently remaining to the east of the 180° longitude, cutting through American Samoa and Samoa.
  • Finally, the line curves southwest, tracing the 180° meridian until it reaches Antarctica.

180° Meridian

  • In 1884, the International Meridian Conference implemented the International Date Line (IDL) as an imaginary boundary, approximately tracing the 180° meridian and distinct from other meridians, including the Prime Meridian.
  • Attended by representatives from 26 nations, the conference selected the 180° longitude due to its passage through the expansive Pacific Ocean. The line was purposefully zig-zagged to ensure that neighboring nations, particularly island countries, remained within the same day and date.

Time and date across International Date Line

  • Crossing the International Date Line (IDL) results in gaining or losing a day, depending on the direction of travel.
  • Westward travel across the IDL leads to gaining a day, while eastward travel causes a day to be lost.
  • Example: Traveling east from Wake Island to the Hawaiian Islands on June 25 results in reverting to June 24 upon crossing the IDL. Conversely, a westward journey leads to arrival at Wake Island on June 26.
  • Traveling west from the IDL results in gaining one hour for every 15° of longitude crossed, while traveling east leads to the loss of one hour.
  • Westward travel without adjusting time back by an hour for each 15° meridian results in gaining an additional day upon returning home, as observed during Ferdinand Magellan’s 1522 expedition.
  • Traveling eastward around the globe leads to a loss of 24 hours or one day.
  • During the 10:00 to 11:59 UTC time period, three separate calendar dates coexist for two hours each day.
  • Example: At 10:30 UTC on Friday, it is simultaneously 11:30 PM Thursday in American Samoa, 12:30 AM UTC Saturday in Kiritimati, and 6:30 AM UTC Friday in New York.
  • Baker Island and Howland Island operate on the Earth’s latest time at UTC-12, while Kiritimati (Kiribati) is among the first places to enter a new day at UTC +14.


Q: What is local time?

A: Local time refers to the time of a specific place determined by the position of the sun overhead.

Q: What is standard time?

A: Standard time is the official time established by law or general usage in a region or country, often used for civil purposes.

Q: What is the difference between local time and standard time?

A: Local time varies based on the longitudinal position of a place, while standard time is a uniform time established for a broader region, country, or time zone.

Q: What distinguishes local and standard time from the equator and the prime meridian?

A: Local and standard time are based on the longitudinal position of a place, while the equator and prime meridian determine a location’s geographical coordinates on the Earth’s surface.

Q: How are the equator and prime meridian related to local and standard time?

A: The equator and prime meridian play a significant role in defining the geographical position of a place, while local and standard time relate to the longitudinal difference and the official time used in specific regions.

Q: What is the time difference between Indian Standard Time (IST) and Eastern Standard Time (EST)?

A: The time difference between IST and EST is typically 9.5 hours, with IST ahead of EST.

Q: How can I convert Indian Standard Time (IST) to Eastern Standard Time (EST)?

A: To convert IST to EST, subtract 9.5 hours from IST to obtain the corresponding time in EST.

Q: What is the relationship between Indian Standard Time (IST) and Coordinated Universal Time (UTC)?

A: IST is typically 5 hours and 30 minutes ahead of Coordinated Universal Time (UTC).

Q: How do I convert Indian Standard Time (IST) to Coordinated Universal Time (UTC)?

A: To convert IST to UTC, subtract 5 hours and 30 minutes from IST to obtain the corresponding time in UTC.

Q: How does Indian Standard Time (IST) relate to Greenwich Mean Time (GMT)?

A: IST is typically 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).

Q: How can I convert Indian Standard Time (IST) to Greenwich Mean Time (GMT)?

A: To convert IST to GMT, subtract 5 hours and 30 minutes from IST to obtain the corresponding time in GMT.

Q: What is the time difference between Indian Standard Time (IST) and UK Time?

A: The time difference between IST and UK Time varies depending on the UK’s daylight saving time (GMT/BST), ranging from 4 hours and 30 minutes to 5 hours and 30 minutes.

Q: How do I convert Indian Standard Time (IST) to UK Time?

A: To convert IST to UK Time, subtract the corresponding hours and minutes difference based on the UK’s current time zone.

Q: What is the significance of Indian Standard Time (IST) in terms of its geographical path?

A: Indian Standard Time (IST) is determined by the 82.5° E longitude, passing through Mirzapur, near Allahabad in the state of Uttar Pradesh, India.

Q: What is the specific longitude of the International Date Line (IDL)?

A: The International Date Line is generally observed near the 180° line of longitude, marking the transition between calendar days.

Q: How is the International Date Line (IDL) defined?

A: The International Date Line is an imaginary line on the Earth’s surface, roughly following the 180° line of longitude, where the date changes by one day when crossed from the east to the west or vice versa.

Q: What is the significance of the International Date Line (IDL) in UPSC examinations?

A: The International Date Line is a key geographical concept often covered in UPSC examinations, especially in questions related to global time zones, geography, and international trade and communication.

Q: Can the International Date Line (IDL) be seen on a world map?

A: Yes, the International Date Line is depicted on most world maps as an irregular line running from the North Pole to the South Pole, primarily crossing the Pacific Ocean.

Q: Which specific countries and territories does the International Date Line (IDL) pass through?

A: The International Date Line passes through various countries and territories in the Pacific region, including Fiji, Tonga, Samoa, Kiribati, and the Republic of Vanuatu, among others.

Q: What is the purpose and significance of Daylight Saving Time (DST)?

A: Daylight Saving Time is a practice where clocks are adjusted to make better use of daylight during the evening hours. It is aimed at conserving energy and making better use of natural daylight.

Q: When does Daylight Saving Time typically start in different regions?

A: Daylight Saving Time starts at various times in different regions. It commonly begins in the spring, usually around March or April, depending on the specific laws and regulations of each country or region.

Q: What is the time offset during Daylight Saving Time (DST)?

A: During Daylight Saving Time, clocks are typically adjusted by one hour forward, meaning the local time is one hour ahead of the standard time, providing an extra hour of daylight in the evening.

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