Local time refers to the time in a certain area, which is determined by the position of the sun in the sky and the line of longitude that passes through it. This means that local time varies from region to region, so it is important to have a standard time system. Standard time is based on the earth’s central meridian and is used to create time zones that are usually 15 degrees or one hour apart in time.
The world is divided into 24 standard time zones, but some countries with special shapes and locations must deviate from this standard. For example, larger countries such as Canada, the US, and the US must adopt multiple time zones due to their significant east-west stretch. Knowing your local time and time zones is important for travelers, and a useful way to remember the time zone difference is through the abbreviations EGA (East-Gain-Add) and WLS (West-Lose-Subtract).
Local Time
As the name implies, local time refers to the time in a specific region, which is based on the line of longitude passing through it. It is calculated based on the meridian running through a particular place and is determined by the position of the sun in the sky. The length of the shadow cast by the sun varies throughout the day, with the shortest shadow occurring at noon. When the sun is directly overhead, it is noon at that location. However, since noon occurs at different times in different meridians, local time varies from region to region.
The earth completes one rotation of 360° in 24 hours or one day, which means it moves through 15° in one hour or 1° in 4 minutes. As the earth rotates from west to east, every 15° we travel eastwards, and local time is advanced by 1 hour. On the other hand, if we go westwards, local time is retarded by 1 hour. Therefore, places east of Greenwich gain time and see the sun earlier, while places west of Greenwich lose time and see the sun later.
To determine local time from G.M.T., we add or subtract the difference in the number of hours from the given longitude. A useful way to remember this is through the acronym EGA (East-Gain-Add) for adding and WLS (West-Lose-Subtract) for subtracting. For instance, when it is noon in London (longitude 0°5W), the local time in Madras (80°E) will be 5 hours and 20 minutes ahead of London, or 5.20 p.m. However, the local time in New York (74°W) will be 4 hours and 56 minutes behind London, or 7.04 a.m. Thus, while Londoners are having lunch, Indians will be having dinner, and New Yorkers will be having breakfast.
The rotation of the earth around the sun means that different places experience different times of day at any given point in time. There are various ways to determine the longitude of a place, but a simple method is to compare local time with G.M.T. by listening to B.B.C. radio. For example, if G.M.T. is 8.00 a.m. and local time is noon on a ship, it means that the captain of a ship amid the ocean is four hours ahead of Greenwich and must be east of Greenwich. Therefore, the longitude of the ship is 4 × 15° or 60°E.
Standard Time and Time Zones
If every town were to follow its own meridian, there would be significant discrepancies in local time between different towns. For instance, if it were 10 a.m. in Georgetown, Penang, it would be 10:10 a.m. in Kota Bharu, with a difference of 21° in longitude. In countries such as Canada, China, India, the U.S.A, and U.S.S.R., the disparities alone would create chaos and inconvenience, especially for travelers who would need to adjust their watches repeatedly to keep their appointments.
To prevent such confusion, countries adopt a system of standard time. Most countries use the central meridian of their country as their standard time. In India, the standard time is based on the meridian of 82.5° east, which is 5 hours and 30 minutes ahead of the Greenwich Mean Time.
The world is divided into 24 standard time zones, with each zone differing from the next by 15° in longitude or one hour in time. Although most countries follow this standard, some countries with peculiar shapes and locations have to deviate reasonably from the standard time zones. For example, larger countries such as the U.S.A., Canada, and U.S.S.R., which have a significant east-west stretch, have to adopt several time zones.
U.S.S.R., the largest country, which covers almost 165° of longitude, is divided into eleven time zones. When it is 10 p.m. on Monday in Leningrad, it will be almost 7 a.m. the following Tuesday morning in Vladivostok. Travelers on the Trans-Siberian Railway must adjust their watches almost a dozen times before they reach their destination. Canada and U.S.A. have five time zones each: Atlantic, Eastern, Central, Mountain, and Pacific time zones. The difference in local time between the Atlantic and Pacific coasts is approximately five hours.
Conclusion
Understanding local time and standard time is essential for individuals, especially travelers who need to adjust their watches repeatedly to keep their appointments. The adoption of standard time zones has created uniformity in timekeeping across countries, making it easier for people to schedule and coordinate activities. Despite the challenges of adjusting to different time zones, technology has made it easier to keep track of time and stay connected with people worldwide. Overall, the study of time and time zones is fascinating and highlights the complexities of our planet’s movements and their impact on our daily lives.
FAQs
Q.1 What is local time?
Answer: Local time refers to the time in a specific region, which is based on the line of longitude passing through it. It is calculated based on the meridian running through a particular place and is determined by the position of the sun in the sky.
Q.2 How is local time determined?
Answer: Local time is determined by the position of the sun in the sky and is calculated based on the meridian running through a particular place. The length of the shadow cast by the sun varies throughout the day, with the shortest shadow occurring at noon. When the sun is directly overhead, it is noon at that location.
Q.3 How does the rotation of the earth affect local time?
Answer: The earth completes one rotation of 360° in 24 hours or one day, which means it moves through 15° in one hour or 1° in 4 minutes. As the earth rotates from west to east, every 15° we travel eastwards, and local time is advanced by 1 hour. On the other hand, if we go westwards, local time is retarded by 1 hour.
Q.4 What is the relationship between local time and longitude?
Answer: Local time varies from region to region because noon occurs at different times in different meridians. To determine local time from G.M.T., we add or subtract the difference in the number of hours from the given longitude. Places east of Greenwich gain time and see the sun earlier, while places west of Greenwich lose time and see the sun later.
Q.5 What is the problem with every town following its own meridian for timekeeping?
Answer: If every town followed its meridian, there would be significant discrepancies in local time between different towns. For example, the time difference between Georgetown and Kota Bharu in Malaysia is 10 a.m. and 10:10 a.m., respectively, despite being only 21° apart in longitude. This would cause chaos and inconvenience for travelers who would have to adjust their watches repeatedly to keep their appointments.
Q.6 What is the solution to prevent confusion in timekeeping across different towns and countries?
Answer: To prevent confusion, countries adopt a system of standard time based on the central meridian of their country. This helps maintain a consistent time across the country and reduces the need for travelers to adjust their watches frequently. The world is divided into 24 standard time zones, with each zone differing from the next by 15° in longitude or one hour in time.
Q.7 What is the standard time for India, and how is it calculated?
Answer: In India, the standard time is based on the meridian of 82.5° east, which is 5 hours and 30 minutes ahead of the Greenwich Mean Time. This meridian was chosen because it passes through the middle of the country and is close to the city of Allahabad.
Q.8 Why do some countries, such as the U.S.A., Canada, and Russia, have to adopt several time zones?
Answer: Some larger countries with a significant east-west stretch have to adopt several time zones to maintain a consistent time across the country. For example, the U.S.A., and Canada, have five and Russia has 11 time zones due to their size and shape.
Q.9 How many time zones does Russia have, and what is the time difference between Leningrad and Vladivostok?
Answer: Russia is divided into eleven time zones due to its vast size, covering almost 165° of longitude. The time difference between Leningrad and Vladivostok is almost 7 hours, with it being 10 p.m. on Monday in Leningrad and almost 7 a.m. on Tuesday in Vladivostok. Travelers on the Trans-Siberian Railway must adjust their watches almost a dozen times before they reach their destination.
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