The Earth rotates from West to East ↻
Earth rotates 360° in 24 hours. This rotation causes day and night, and is the reason we have time zones.
360° ÷ 24 hours = 15° per hour
Every 15° of longitude equals 1 hour of time difference.
Every 1° of longitude equals 4 minutes.
As you move East from Greenwich (0°), time increases (gets ahead).
Example: India (82.5°E) is +5:30 hours ahead of Greenwich.
As you move West from Greenwich (0°), time decreases (falls behind).
Example: New York (74°W) is -5 hours behind Greenwich.
The Prime Meridian (0° longitude) passes through Greenwich, London. All time zones are measured from this line. GMT is the reference point for world time.
The 180° longitude line is the International Date Line. When you cross it going East → subtract 1 day. Going West → add 1 day.