Local Time And Standard Time | Time Zones Explained | Geography NCERT | UPSC Prelims and Mains 2023

Summary

The video explores the relationship between longitudes and time, explaining how local time is determined based on the Earth's rotation and the Sun's movement. It highlights the concept of Standard Time and time zones, emphasizing their importance in daily activities, such as scheduling trains. The video also discusses Daylight Saving Time (DST), which adjusts clocks to capture more sunlight during the warmer months, and how seasons and Earth's tilt affect day lengths. The practice of DST, introduced during World War I, is widely used in various regions, enhancing energy efficiency and daily routines.

Takeaways

• 😀 Longitudes help us in determining locations and tracking time.
• 🌍 Local time is based on the position of the Sun and changes every 4 minutes per degree of longitude.
• 🕒 Thimphu in Bhutan, located at 90° East, is 6 hours ahead of Greenwich Mean Time (GMT).
• 🌐 Local time differences can create problems, especially for organizing timetables for trains and other travel.
• 🕰 Standard Time solves this by using a common time based on a specific longitude called the Standard Meridian.
• 📏 Bhutan follows a standard time based on the 90° East longitude, even though it geographically spans from 88° 44' East to 92° 7' East.
• 🌍 The world is divided into 24 time zones, each with a standard meridian for timekeeping.
• 🇮🇳 India uses the 82° 30' East longitude for its Standard Time, which is 5 hours 30 minutes ahead of GMT.
• 🕰 Countries with large east-to-west extents, like Russia, have multiple time zones to avoid time-related issues.
• 🌞 Daylight Saving Time (DST) is used to make better use of daylight during the warmer months, shifting clocks forward by 1 hour.
• 💡 DST was first implemented by Germany during World War I to conserve energy, and it is now followed by many regions worldwide.

Q & A

How do longitudes help us track time?

Longitudes help track time by determining local time differences based on the Earth's rotation. The Earth takes 24 hours to complete a full rotation, covering 360 degrees. Therefore, it takes 4 minutes for the Sun to travel 1 degree of longitude, creating time differences across locations.

What is local time?

Local time refers to the time at a specific location, determined by its longitude. It changes by 4 minutes for every degree of longitude due to the Earth's rotation, meaning that two locations 1 degree apart will have different local times.

How do we calculate the local time of a place like Thimphu?

To calculate Thimphu's local time, we measure the longitude difference between Greenwich (0° longitude) and Thimphu (90° east). Since the Sun takes 4 minutes to cover 1 degree, for a 90-degree difference, it will take 6 hours for the Sun to pass from Greenwich to Thimphu. Therefore, if it's 12:00 noon in Greenwich, it will be 6:00 PM in Thimphu.

What problem arises when we rely on local time?

The problem with using local time is that each location has a slightly different time based on its longitude. This creates confusion when coordinating activities like train schedules, as each place would have a different time even if they are close to each other.

What is standard time, and why is it important?

Standard time is a fixed time used for a specific region, typically determined by a standard meridian. It simplifies coordination by ensuring that all areas within the same time zone use the same time, regardless of their exact longitude.

Why is Bhutan's time based on the 90° east longitude?

Bhutan's time is based on the 90° east longitude because it is the standard meridian for the country. Despite Bhutan stretching from 88° 44' to 92° 7' east, the whole country uses the same time, which is 6:00 PM when it's 12:00 noon at Greenwich.

How are time zones structured around the world?

The world is divided into 24 time zones, each based on a specific standard meridian, typically located every 15 degrees of longitude. These time zones are coordinated with respect to the prime meridian (0°), and locations east of the prime meridian are ahead of GMT, while those to the west are behind.

Why do some countries have multiple time zones?

Countries with large geographical areas, such as Russia, the United States, and Brazil, follow multiple time zones because the vast east-to-west span means the local time would differ significantly in different regions. Multiple time zones ensure consistency and practicality for scheduling across the country.

What is daylight saving time (DST), and why is it practiced?

Daylight saving time (DST) is the practice of moving the clocks forward by one hour in the spring and back in the autumn. This practice helps maximize daylight during warmer months, allowing people to make better use of daylight hours for activities and save energy.

How does the Earth's tilt relate to daylight saving time?

The Earth's axis is tilted at 23.5 degrees, causing different lengths of day and night across the seasons. During summer, days are longer, and by shifting the clocks forward during DST, people can take advantage of the extra daylight in the evenings.