Earth's rotation defines the 24-hour day. A sidereal day (rotation relative to distant stars) is actually 23 hours 56 minutes 4 seconds — the extra ~4 minutes account for Earth's orbital motion. Our clocks are tuned to the solar day: the time between two solar noons.
Earth's axial tilt of 23.5° drives the seasons, and its orbit of 365.25 days gives us leap years. Time zones divide the planet into 24 slices of 15° longitude, each offset by 1 hour. Atomic clocks on Earth's surface tick slightly faster than those on satellites at altitude — a relativistic effect corrected daily in GPS systems.
Frequently Asked Questions
How long is an Earth day?
A solar day is exactly 24 hours. A sidereal day (relative to stars) is 23h 56m 4s.
How many time zones does Earth have?
Earth has 24 main time zones, each 15° of longitude wide, though political boundaries add more.
Does gravity affect time on Earth?
Yes — clocks at higher altitude (lower gravity) tick slightly faster, a real relativistic effect corrected in GPS satellites.