Convert between time units
A regular year has 31,536,000 seconds (365 days × 24 hours × 60 minutes × 60 seconds). A leap year has 31,622,400 seconds. The average year (accounting for leap years) has about 31,557,600 seconds.
1 second = 1000 milliseconds (ms) = 1,000,000 microseconds (µs) = 1,000,000,000 nanoseconds (ns). Computer operations are measured in nanoseconds; human reaction time is about 200-300 milliseconds.
A year is a leap year if divisible by 4, except century years must be divisible by 400. So 2000 was a leap year, but 1900 wasn't. This keeps our calendar aligned with Earth's orbital period.
A solar day (24 hours) is based on the Sun's position—noon to noon. A sidereal day (23h 56m 4s) is based on stars. The difference exists because Earth orbits the Sun while rotating.
Multiply the decimal by 60 to get minutes. For example, 2.75 hours: 0.75 × 60 = 45 minutes, so 2.75 hours = 2 hours 45 minutes. For seconds, repeat with remaining decimal minutes.
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