Scientific time tool
Convert a clock time into the fraction of a day elapsed since midnight, then convert a decimal day back into HH:MM:SS.
0.8131944444
Fraction of one civil day elapsed since midnight.
19:31:00
Values outside 0 to 1 are clamped to the nearest day boundary.
Astronomers use Julian Day numbers to put observations on one continuous timeline. The integer identifies the day and the fractional part records the time within that day, so noon is 0.5, 18:00 is 0.75, and values near 1.0 are just before the next midnight. Scientists and statisticians use the same idea when a daily cycle is easier to model as a number from 0 to 1 than as separate hour, minute, and second fields.
In JavaScript, the arithmetic is the same: Date.now() / 86400000 expresses Unix time in days, and the fractional remainder is the elapsed fraction of the current UTC day. This tool uses local clock input instead, but the denominator is still 86,400 seconds per day.
Decimal time also has a civil-history branch. The French Republican calendar tried a decimal clock with ten hours per day, one hundred minutes per hour, and one hundred seconds per minute. It was rational and short-lived; ordinary 24-hour clocks won, while decimal fractions stayed useful in computation.