Shop Windows to the Universe

Young Voices for the Planet DVD in our online store includes 8 films where students speak out and take action on climate change.

AU


AU, which stands for "astronomical unit", is a unit for measuring distance. One AU is the average distance from the Sun's center to the Earth's center. It is equal to 149,597,871 km (92,955,807 miles).

AUs are often more convenient to use than kilometers when measuring large distances such as those in space. In this case kilometers are just too small - it would be like measuring the distance from Boston to San Francisco in inches. AUs simply make a measurement easier to understand and give you something to compare it to.

For example, Saturn's orbit around the Sun has an average radius of 9.5 AU, which means that Saturn is about ten times farther from the Sun than Earth is. The average distance from the Sun to distant Pluto is about 40 AU. Mercury, the planet closest to the Sun, orbits at an average distance of 0.39 AU.

AUs are generally used for measurements of distances within our Solar System. Distances to stars are much larger, and are expressed in terms of light years. One light year is equal to more than 63,000 AUs. The nearest star, Proxima Centauri, is just over 4 light years away.


Last modified May 21, 2004 by Randy Russell.

Shop Windows to the Universe Science Store!

Learn about Earth and space science, and have fun while doing it! The games section of our online store includes a climate change card game and the Traveling Nitrogen game!

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

Hubble Space Telescope

The Hubble Space Telescope (HST) is really neat! It was first launched in 1990, but scientists started building it in the 1970's! We have found all kinds of objects like stars, nebulae and galaxies. The...more

Apollo 11

Apollo 11 was the first mission that landed a person on the moon. On July 16, 1969, the U. S. rocket Saturn 5 was launched carrying the lunar landing module Eagle. The Eagle was released and it reached...more

Apollo 12

Apollo 12 was launched on Nov. 14, 1969 and arrived at the Moon three days later. Astronauts Charles Conrad and Alan Bean descended to its surface, while Richard Gordon remained in lunar orbit aboard the...more

Apollo 15

Apollo 15 marked the start of a new series of missions from the Apollo space program, each capable of exploring more lunar terrain than ever before. Launched on July 26, 1971, Apollo 15 reached the Moon...more

Deep Impact Mission

NASA chose Deep Impact to be part of a special series called the Discovery Program. This program is for cheap, scientific projects. In May 2001, NASA said it was ok to start with mission development for...more

Galileo

Galileo was a spacecraft that orbited Jupiter for eight years. It made many discoveries about Jupiter and its moons. Galileo was launched in 1989, and reached Jupiter in 1995. The spacecraft had two parts....more

Lunar Orbiter

During 1966 through 1967, five Lunar Orbiter spacecrafts were launched, with the purpose of mapping the Moon's surface in preparation for the Apollo and Surveyor landings. All five missions were successful,...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA