Browse Definitions :
Definition

astronomical unit (AU)

An astronomical unit (AU) is the mean distance between the center of the Earth and the center of the sun. The actual distance varies depending on the time of year, because the Earth's orbit around the sun is not a perfect circle. The mean, or average, separation is approximately 1.4959787 x 10 11 meters, which is 1.4959787 x 10 8 kilometers or 9.2955807 x 10 7 miles.

Distances within the solar system are commonly measured in AU. Mercury, the innermost planet, orbits at a mean distance of about 0.4 AU from the sun, while Neptune, one of the most distant planets known, has an average orbital radius of about 30 AU. Interstellar and intergalactic distances are expressed in light-years or parsec s.

Interestingly, the Earth is closest to the Sun during the month of January, and farthest during July. The variation is about ±1 percent of the mean distance. Seasonal weather results from the tilt of the Earth's axis, and is not significantly affected by the distance of the planet from the sun.

Also see the Table of Physical Units and Constants.

This was last updated in January 2011
SearchCompliance
  • ISO 31000 Risk Management

    The ISO 31000 Risk Management framework is an international standard that provides businesses with guidelines and principles for ...

  • pure risk

    Pure risk refers to risks that are beyond human control and result in a loss or no loss with no possibility of financial gain.

  • risk reporting

    Risk reporting is a method of identifying risks tied to or potentially impacting an organization's business processes.

SearchSecurity
SearchHealthIT
SearchDisasterRecovery
  • What is risk mitigation?

    Risk mitigation is a strategy to prepare for and lessen the effects of threats faced by a business.

  • fault-tolerant

    Fault-tolerant technology is a capability of a computer system, electronic system or network to deliver uninterrupted service, ...

  • synchronous replication

    Synchronous replication is the process of copying data over a storage area network, local area network or wide area network so ...

SearchStorage
Close