07. How do scientists know the number of hours and days on each of the planets? (A K2S Question)
From The Space Library
If we define the length of a second with a very precise clock, and if we agree that there are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day, then those time measurements will always be the same unless we move near the speed of light. These standard lengths of seconds, minutes, hours, and days would be the same on all planets. In fact the standard length of a second on Earth is no longer based on day or night, but on the ticking of an atomic clock. An atomic clock ticks when atoms of the element cesium vibrate back and forth. Since atom vibrations are very fast and always the same, they allow us to keep time accurate to one billionth of a second per day! If we now measure the time it takes a planet to turn once on its axis, we will find that different planets take different numbers of hours, minutes, and seconds to make the turn. Scientists have observed all of the planets in our solar system for many years and timed their rotations. So we know the lengths of days on all of the planets, but we still measure those lengths in the hours, minutes, and seconds that we define here on Earth.
Answer provided by Luke Keller, Ph.D.
Question and Answer extracted from the book Kids to Space - by Lonnie Schorer
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