# How reliable are our alarm clocks - When will the length of a day be 26 hours?

Asked by mattbrowne (31732) March 31st, 2009

The Moon is Earth’s only natural satellite and the fifth largest satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is 384,403 km, about thirty times the diameter of the Earth.

Observing members: 0 Composing members: 0

I’m reading between the lines… but it’s not helping?

Lightlyseared (34678)

What does the moon have to do with the length of the day?

Les (10005)

I’ll just answer the question because I have no idea what the detail section means.

The length of a day is actually getting shorter. Studies have been done on people wherein they were not exposed to the outside or any timekeeping device for several months. they actually reset to follow a 25 hour day, as opposed to the 24 hour day.

KatawaGrey (21483)

Well, if your alarm clock is a Quartz clock, it will remain relatively accurate as long as the quartz remains unmodified or undamaged. With normal usage, other components of the clock will deteriorate before the accuracy of the timepiece is at risk of serious misalignment (I’ll define serious as being an error of 60 seconds).

When will the length of the day be 26 hours? Well, I first ask you to define what “day” means, as it is not a proper SI unit. The second, however, is an SI unit, and one “day” as you use it here is equal to 86,400 seconds. The primary cause of our length of day is the rotation of Earth around its axis (extending to the Earth rotating around the Sun, of course), so to change the number of seconds this takes to do, we would need to change the circumstances which influence the rotation of the Earth. I propose that such changes are impossible for humans to inflict at our current technological level without causing serious repercussions which may end all of humanity’s life. As such, I conclude that the length of day will never be 26 hours on Earth.

dynamicduo (14392)

Here’s the reason: The moon slows down the rotation of the Earth. In the past a day only had 20 hours (and even less) and in the future a day will have more than 24 hours. But I don’t know the exact formula. Will a 26-hour day occur in one million years? 100 million years?

mattbrowne (31732)

@mattbrowne Can you show me proof as to the 20 hour day claim? I am trying to find some but cannot find any, and I feel that’s critical to this discussion.

dynamicduo (14392)

The presence of the moon (which has about 1/81 the mass of the Earth), is slowing Earth’s rotation and lengthening the day by about 2 ms every one hundred years.

But I’ve heard it’s not linear so we can’t just multiply the 2 ms to make a precise prediction about the future. Same for the past.

mattbrowne (31732)

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