SpaceTwo kinds of day
The rotation period is the time a planet takes to turn once compared with the distant stars. The length of day is the time from one noon to the next. They differ because a planet moves along its orbit while it spins, so it must turn a little more, or less, to bring the Sun back overhead. For Earth the two are close: 23.9 and 24 hours.
The shortest and longest days
Among the planets, Jupiter has the shortest day, 9.9 hours. Mercury has the longest, 175.9 Earth days.
Mercury: a day longer than its year
Mercury turns once in 1,407.6 hours, which is 58.6 Earth days, but its year is only 88 Earth days. Counted from noon to noon, one day on Mercury lasts 175.9 Earth days: about two of its own years.
Venus: backwards and slow
The minus sign beside Venus means that it turns the opposite way to Earth. One turn takes 243 Earth days, longer than its year of 224.7 days. On Venus the Sun would rise in the west.
The giants spin fast
Jupiter, the largest planet, turns once in just 9.9 hours, and Saturn in 10.7. Uranus (17.2 hours, also with a minus sign) and Neptune (16.1 hours) are not far behind.
Years grow with distance
The farther a planet is from the Sun, the longer its path and the slower it travels: Mercury moves at 47.4 km/s and Neptune at only 5.4 km/s. So Neptune takes 163.7 Earth years to go round once. A person would not live to see one birthday there. Find your own age on each planet with the age calculator.