A diagram showing the different rotation axes.

# The Earth's Rotation

The Earth is rotating around an axis (called its rotational axis). Some objects rotate about a horizontal axis, like a rolling log. Some objects, such as a skater, rotate about a vertical axis. The Earth's axis is tipped over about 23.5° from vertical.

How do we define up and down in space? What would "vertical" mean? For the Earth, we can think of vertical as straight up and down with respect to the plane in which the Earth orbits the Sun (called the ecliptic).

Earth's rotational axis points in the same direction relative to the stars, so that the North Pole points towards the star Polaris. Think of the Earth as a spinning top, tipped over to one side. Over very long time periods (thousands of years) the direction of Earth's axis slowly changes due to precession.

The Earth rotates around once in 24 hours - that's a rate of 1000 miles per hour!. The time it takes for the Earth to rotate completely around once is what we call a day. It's Earth's rotation that gives us night and day.

The combined effect of the Earth's tilt and its orbital motion result in the seasons.

## Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

## What Causes the Seasons?

The Earth's orbit is in the shape of an ellipse (a stretched out circle), so that sometimes the Earth is closer to the Sun than at other times. Is this the cause of the seasons? You can imagine that if...more

## What is the distance from the Earth to the Sun when the Earth is at perihelion and when it is at aphelion? At what month is the Earth closest to the Sun? What is the circumference of the Earth? How fast is the Earth moving about its axis; how about around the Sun?

Scientists use fancy words to describe things sometimes. The Earth doesn't orbit the Sun in a perfect circle. So, there is a point when the Earth is closest to the Sun and farthest from the Sun. Scientists...more

## Mercury's Poles

Most planets are tilted. Their North and South Poles are not straight up and down. Earth is tilted a medium amount. Uranus is tilted a lot. Mercury is hardly tilted at all. It is tilted less than any other...more

## The Magnetic Poles of Mercury

Mercury has a magnetic field. Its field is weak. Earth's magnetic field is tilted. So is Mercury's. That means Mercury's magnetic poles are not in the same place as its geographic poles. Mercury has a...more

## Native American Astronomy

People have been living in North America for a long, long time. The first people to live there were the Native Americans. They didn't have clocks or calendars so they watched tides, the Sun, the Moon,...more

## Archeoastronomy

Man has always observed the sky. By watching the Sun and Moon, early man could tell what season was coming next. They had to know this to be able to farm and hunt. Archeoastronomy started in the 1960's...more

## The Stones of Carnac

The stones of Carnac, France, are very famous because there are a lot of them and because they are so old! The oldest stones found in Carnac are from about 4,500 B.C. That's older than the stones at Stonehenge!...more

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