Moon and Jupiter
If you've ever thought that there just aren't enough hours in the day, then you probably wouldn't have been happy a few hundred million years ago. That's because the day was even shorter than it is now.
The day is being stretched out by the gravitational interaction between Earth and the Moon -- specifically, the tides. The Moon's gravity pulls at Earth's oceans, creating "bulges" of water that travel around the planet. The bulges slosh into the landmasses, creating friction that causes the planet to rotate more slowly.
Confirmation of this effect is found in ancient beds of fossilized coral.
Some types of coral produce yearly growth bands that are like tree rings. Each band also contains a thin layer for each day. By counting the layers in corals of different ages, scientists can determine the number of days in a given year.
The fossils show that 300 million years ago, the year consisted of about 390 days, each of which lasted about 22 hours. And 500 million years ago, each day was only about 21 hours long.
The slow-down of Earth's rotation continues even now -- increasing the length of the day by about one second for every 50,000 years.
Look for the Moon high in the south as night falls, with the brilliant planet Jupiter to its left. They set around midnight. We'll have more about the Moon and Jupiter -- plus a meteor shower -- tomorrow.
Script by Damond Benningfield, Copyright 2010
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