Standard Time and Time Zones!
Problem with Local Time:
Imagine if every town used its own local time based on its exact longitude.
Towns very close to each other (but slightly different longitudes) would have slightly different times.
Example: Georgetown & Kota Bharu (very close, but ~2.5° longitude difference = ~10 minutes time difference).
For small distances, this might be just a little confusing.
Big Problem in Big Countries!
In large countries that stretch a lot from East to West (like Canada, USA, China, India, Russia), using only local time would be a disaster!
Time differences across the country would be huge.
Travel Nightmare: Imagine traveling across a big country and having to change your watch many times a day just to be on "local time" - super annoying and confusing! Trying to schedule meetings or travel would be crazy.
Solution: Standard Time!
To fix this, countries use Standard Time.
Instead of everyone using their own local time, a whole region or country agrees to use the same time.
This makes things much simpler for everyone living, working, and traveling within that region.
How Standard Time is Chosen:
Most countries choose a central meridian of longitude that runs through their country.
They set their standard time based on the local time of that central meridian.
India's Standard Time Example:
India uses 82.5° East longitude as its standard meridian.
Indian Standard Time (IST) is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT). This is based on the local time at 82.5°E.
So, all of India (mostly) uses this one standard time, even though local time varies a bit from west to east of India.
World Time Zones:
The whole world is divided into roughly 24 Standard Time Zones.
Each time zone is about 15° of longitude wide.
Each time zone is usually 1 hour different from the zones next to it.
This system makes it easier to manage time differences across the globe.
Not Always Perfect Boxes:
Time zones are mostly based on 15° longitude lines, but they aren't always perfectly straight lines on a map.
Reasonable Deviations: Sometimes, countries adjust time zone borders to fit their boundaries, or for practical reasons. Time zones can have irregular shapes.
Large Countries = Multiple Time Zones:
Very wide countries (east to west) have to use multiple time zones.
Examples:
Russia (USSR): Huge east-west stretch. Has 11 time zones! Imagine the time difference from one side to the other. Example: Leningrad (west) 10 PM Monday vs. Vladivostok (east) 7 AM Tuesday! Trans-Siberian Railway travelers have to change watches many times.
Canada & USA: Both have 5 main time zones each: Atlantic, Eastern, Central, Mountain, Pacific.
Time difference between the Atlantic coast and Pacific coast of USA/Canada is about 5 hours!
In simple words: Standard time and time zones are used to make time simpler and less confusing, especially in big countries and for world travel. Instead of every place having its own slightly different local time, regions agree to use the same "standard time." The world is divided into time zones roughly based on longitude lines, each about an hour apart from the next. Big countries need multiple time zones because the time difference from one side to the other is too large to ignore!