Leap Year & Earthâs Movement : Solar & Lunar Calendar Systems : Time Zones & Standard Time
Leap Year & Earth’s Movement
Why Do We Have Leap Year ?
The Earth takes about 365.25 days to complete one revolution around the Sun. The extra 0.25 day each year becomes 1 extra day in 4 years. That extra day is added to February (29 days).
āĻĒā§āĻĨāĻŋā§ąā§ā§ā§ āĻ¸ā§ā§°ā§āĻ¯ā§° āĻāĻžā§°āĻŋāĻāĻĢāĻžāĻ˛ā§ āĻāĻāĻž āĻāĻā§āĻā§° āĻ¸āĻŽā§āĻĒā§ā§°ā§āĻŖ āĻā§°āĻŋāĻŦāĻ˛ā§ āĻĒā§ā§°āĻžāĻ¯āĻŧ ā§Šā§Ŧā§Ģ.ā§¨ā§Ģ āĻĻāĻŋāĻ¨ āĻ˛āĻžāĻā§āĨ¤ āĻĒā§ā§°āĻ¤āĻŋāĻŦāĻā§° ā§Ļ.ā§¨ā§Ģ āĻĻāĻŋāĻ¨ āĻāĻŽāĻž āĻšā§ ā§Ē āĻŦāĻā§°āĻ¤ ā§§ āĻĻāĻŋāĻ¨ āĻšāĻ¯āĻŧāĨ¤ āĻ¸ā§āĻ āĻĻāĻŋāĻ¨āĻā§ āĻĢā§āĻŦā§ā§°ā§ā§ąāĻžā§°ā§ āĻŽāĻžāĻšāĻ¤ (ā§¨ā§¯ āĻĻāĻŋāĻ¨) āĻ¯ā§āĻ āĻā§°āĻž āĻšāĻ¯āĻŧāĨ¤
Leap Year Rule
A year is a leap year if it is divisible by 4. Example: 2020 | 2024
āĻ¯āĻŋ āĻŦāĻā§° ā§Ēā§°ā§ āĻŦāĻŋāĻāĻžāĻā§āĻ¯, āĻ¸ā§āĻāĻā§ Leap Year āĻšāĻ¯āĻŧāĨ¤ āĻāĻĻāĻžāĻšā§°āĻŖ: 2020 | 2024
Earth’s Rotation & Revolution
Rotation: Earth spins on its axis. : āĻĒā§āĻĨāĻŋā§ąā§ āĻ¨āĻŋāĻā§° āĻ āĻā§āĻˇā§° āĻāĻĒā§°āĻ¤ āĻā§ā§°ā§āĨ¤ , 24 hours = 1 day : ā§¨ā§Ē āĻāĻŖā§āĻāĻž = ā§§ āĻĻāĻŋāĻ¨
Revolution: Earth moves around the Sun. : āĻĒā§āĻĨāĻŋā§ąā§ āĻ¸ā§ā§°ā§āĻ¯ā§° āĻāĻžā§°āĻŋāĻāĻĢāĻžāĻ˛ā§ āĻā§ā§°ā§āĨ¤ , 365 days = 1 year : ā§Šā§Ŧā§Ģ āĻĻāĻŋāĻ¨ = ā§§ āĻŦāĻā§°
Leap year keeps our calendar accurate. Leap year āĻā§āĻ˛ā§āĻŖā§āĻĄāĻžā§° āĻ¸āĻ āĻŋāĻ ā§°āĻžāĻā§āĨ¤
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Solar & Lunar Calendar Systems
Solar Calendar
Based on Earth’s revolution around the Sun. : Solar Calendar āĻ¸ā§ā§°ā§āĻ¯ā§° āĻāĻžā§°āĻŋāĻāĻĢāĻžāĻ˛ā§ āĻĒā§āĻĨāĻŋā§ąā§ā§° āĻāĻā§āĻā§°ā§° āĻāĻĒā§°āĻ¤ āĻāĻ§āĻžā§°āĻŋāĻ¤āĨ¤
1 year ≈ 365 days : ā§§ āĻŦāĻā§° ≈ ā§Šā§Ŧā§Ģ āĻĻāĻŋāĻ¨
Example: Gregorian Calendar
Lunar Calendar
Based on the Moon’s cycle around the Earth. : Lunar Calendar āĻāĻ¨ā§āĻĻā§ā§°ā§° āĻĒā§āĻĨāĻŋā§ąā§ā§° āĻāĻžā§°āĻŋāĻāĻĢāĻžāĻ˛ā§ āĻāĻā§āĻā§°ā§° āĻāĻĒā§°āĻ¤ āĻāĻ§āĻžā§°āĻŋāĻ¤āĨ¤
1 month ≈ 29.5 days : ā§§ āĻŽāĻžāĻš ≈ ā§¨ā§¯.ā§Ģ āĻĻāĻŋāĻ¨
12 lunar months ≈ 354 days : ā§§ā§¨āĻāĻž Lunar āĻŽāĻžāĻš ≈ ā§Šā§Ģā§Ē āĻĻāĻŋāĻ¨
Key Difference
Solar Calendar: Based on Sun - āĻ¸ā§ā§°ā§āĻ¯ā§° āĻāĻĒā§°āĻ¤ āĻāĻ§āĻžā§°āĻŋāĻ¤ : Solar year = 365 days
Lunar Calendar: Based on Moon - āĻāĻ¨ā§āĻĻā§ā§°ā§° āĻāĻĒā§°āĻ¤ āĻāĻ§āĻžā§°āĻŋāĻ¤ : Lunar year = 354 days
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Time Zones & Standard Time
Why Time Zones ?
The Earth rotates from west to east. Different places receive sunlight at different times. So the world is divided into time zones.
āĻĒā§āĻĨāĻŋā§ąā§ āĻĒāĻļā§āĻāĻŋāĻŽā§° āĻĒā§°āĻž āĻĒā§āĻŦāĻ˛ā§ āĻā§ā§°ā§āĨ¤ āĻŦāĻŋāĻāĻŋāĻ¨ā§āĻ¨ āĻ āĻžāĻāĻ¤ āĻ¸ā§ā§°ā§āĻ¯ā§° āĻĒā§āĻšā§° āĻŦā§āĻ˛ā§āĻ āĻ¸āĻŽāĻ¯āĻŧāĻ¤ āĻāĻšā§āĨ¤ āĻ¸ā§āĻāĻāĻžā§°āĻŖā§ āĻŦāĻŋāĻļā§āĻŦāĻā§ Time Zone āĻ¤ āĻāĻžāĻ āĻā§°āĻž āĻšā§āĻā§āĨ¤
Greenwich Mean Time (GMT)
The Prime Meridian (0° longitude) passes through Greenwich, England. It is the reference point for world time.
Prime Meridian (ā§Ļ° longitude) āĻāĻāĻ˛ā§āĻŖā§āĻĄā§° Greenwich āĻĻāĻŋāĻ¯āĻŧāĻž āĻā§āĻā§āĨ¤ āĻ āĻŦāĻŋāĻļā§āĻŦā§° āĻŽā§āĻ˛ āĻ¸āĻŽā§ā§° āĻŽāĻžāĻ¨āĻĻāĻŖā§āĻĄāĨ¤
Standard Time
Each country follows a standard time. : āĻĒā§ā§°āĻ¤āĻŋāĻā§ āĻĻā§āĻļā§° āĻ¨āĻŋāĻā§° Standard Time āĻĨāĻžāĻā§āĨ¤
Example: India uses IST (Indian Standard Time) : āĻāĻĻāĻžāĻšā§°āĻŖ: āĻāĻžā§°āĻ¤āĻ¤ IST āĻŦā§āĻ¯ā§ąāĻšāĻžā§° āĻšāĻ¯āĻŧ
IST = GMT + 5 hours 30 minutes : IST = GMT + ā§Ģ āĻāĻŖā§āĻāĻž ā§Šā§Ļ āĻŽāĻŋāĻ¨āĻŋāĻ
Important Rule
Every 15° of longitude = 1 hour time difference : āĻĒā§ā§°āĻ¤āĻŋāĻā§ ā§§ā§Ģ° longitude = ā§§ āĻāĻŖā§āĻāĻž āĻ¸āĻŽā§ā§° āĻĒāĻžā§°ā§āĻĨāĻā§āĻ¯
Key Point
Time zones help coordinate global activities. : Time zone āĻ āĻŦāĻŋāĻļā§āĻŦā§° āĻŦāĻŋāĻāĻŋāĻ¨ā§āĻ¨ āĻĻā§āĻļā§° āĻāĻžāĻŽ āĻ¸āĻŽāĻ¨ā§āĻŦāĻ¯āĻŧ āĻā§°āĻžāĻ¤ āĻ¸āĻšāĻžāĻ¯āĻŧ āĻā§°ā§āĨ¤