Shop Windows to the Universe

Our Glaciers: Then and Now activity kit helps you see the changes taking place in glaciers around the world. See all our activity kits and classroom activities.
A graph showing Kepler's 3rd law.
Click on image for full size
Windows Original.

Kepler's 3rd Law: P2 = a3

Kepler's 3rd law is a mathematical formula. It means that if you know the period of a planet's orbit (P = how long it takes the planet to go around the Sun), then you can determine that planet's distance from the sun (a = the semimajor axis of the planet's orbit), because P2 = a3.

It also tells us that planets which are far away from the Sun have longer periods than those close to the Sun. They move more slowly around the Sun. Look at the formula: if you make the distance, a, large, then P must also be large.

Check out the table of orbital data for the planets. You will notice that the orbital period (P) of the planets gets longer as you go from Mercury to Pluto.

Shop Windows to the Universe Science Store!

The Summer 2010 issue of The Earth Scientist, available in our online store, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Cool It! Game

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

Kepler's Second Law: The Speeds of Planets

Kepler's second law he again discovered by trial and error. After some experimentation, Kepler realized that the line connecting the planet and the Sun sweeps out equal area in equal time. Look at the...more

Native American Astronomy

By 30,000 B.C,. Asian hunter-gatherers had crossed the Bering Strait into North America. These people were the first to inhabit this new land and so they are known as the Native Americans of North America....more

Archeoastronomy

"The movements of the heavenly bodies are an admirable thing, well known and manifest to all peoples. There are no people, no matter how barbaric and primitive, that do not raise up their eyes, take note,...more

The Stones of Carnac

The stones of Carnac, France, are probably the most famous stones markings outside of those found at Stonehenge in England. Where Stonehenge is composed of standing stones, the Carnac area has many different...more

The Cairns of Clava

Not too far from Loch Ness, where the green highlands of Scotland rise and fall there lies three giant cairns of stones. They are called the Balnuaran of Clava. The Balnuaran of Clava, giant tombs encased...more

Cuzco

This is an aerial view of Cuzco. In the center of the picture, the cathedral of Cuzco can be seen. This cathedral was built in the 17th century. Cuzco is located in Southern Peru. It is the ancient capital...more

The Stones of Fossa

The stone structures of England and France are very famous. But, one can also find stone rings, tombs, and dolmen structures in present-day Italy. One such megalithic structure is a site in Fossa, Abruzzo....more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF