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.

## Cool It! Game

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

## What Causes the Seasons?

Let's get rid of some common misconceptions about the seasons. The Earth's orbit is in the shape of an ellipse, so that sometimes the Earth is a little bit closer to the Sun than at other times. Is this...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?

Ok. Let's get some terminology down first. If a body (like the Earth) is orbiting around the Sun, we say it is closest to the Sun at perihelion and farthest from the Sun at aphelion. If a body (like the...more

## Archeoastronomy

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## Mercury's Poles

If Uranus is the "tilted planet", Mercury might be called the "upright planet". The spin axis of Uranus, which defines the locations of the planet's North and South Poles, is tilted by 98°. The spin axis...more

## The Magnetic Poles of Mercury

Mercury has a weak magnetic field. Like Earth's magnetic field, Mercury's dipole field is tilted with respect to the planet's spin axis. This means that Mercury's magnetic poles and its geographic poles...more

## Atmospheric Science Literacy - Essential Principle 4

Earth's atmosphere changes over time and space, giving rise to weather and climate. Fundamental Concept 4.1 Weather is the state of Earth's atmosphere at a particular place and time. The climate of a particular...more

## Atmospheric Science Literacy - Essential Principle 3

Atmospheric circulation transports matter and energy. Fundamental Concept 3.1 Horizontal and vertical energy imbalances in the Earth System produced by unequal heating of Earth's surface create movement...more

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