Sunday, October 9, 2011

Date and Time Parochialism

A day is the length of time it takes a planet to rotate once on its axis.

A year is the length of time it takes a planet to orbit a star.

On Earth, we're so used to the fact that a year is a lot longer than a day here, we are apt to sometimes forget that there's no reason why this has to be the case.

On Mercury, a day is 176 Earth days long. Even more strangely, a Mercury day is 2 Mercury years. In other words, a year is longer than a day there. If you'd grown up on Mercury, your default concept of time ordering would be minute, hour, year, day.


Via the always interesting Astronomy Picture of the Day.

Update: The Dogg makes the excellent point that the interaction of day and year would mean than sunset and sunrise would be a really weird combination of the day and year effects. As would the path of the sun in the sky, for that matter. I demand that NASA commission a simulation and post it in a youtube clip to satisfy my idle curiosity!

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