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

  • information governance

    Information governance is a holistic approach to managing corporate information by implementing processes, roles, controls and ...

  • enterprise document management (EDM)

    Enterprise document management (EDM) is a strategy for overseeing an organization's paper and electronic documents so they can be...

  • risk assessment

    Risk assessment is the identification of hazards that could negatively impact an organization's ability to conduct business.

SearchSecurity

  • cyber espionage

    Cyber espionage, also called cyber spying, is a form of cyber attack that is carried out against a competitive company or ...

  • virus (computer virus)

    A computer virus is malicious code that replicates by copying itself to another program, computer boot sector or document and ...

  • spam trap

    A spam trap is an email address that is used to identify and monitor spam email.

SearchHealthIT

SearchDisasterRecovery

  • risk mitigation

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

  • call tree

    A call tree is a layered hierarchical communication model that is used to notify specific individuals of an event and coordinate ...

  • Disaster Recovery as a Service (DRaaS)

    Disaster recovery as a service (DRaaS) is the replication and hosting of physical or virtual servers by a third party to provide ...

SearchStorage

  • cloud storage

    Cloud storage is a service model in which data is transmitted and stored on remote storage systems, where it is maintained, ...

  • cloud testing

    Cloud testing is the process of using the cloud computing resources of a third-party service provider to test software ...

  • storage virtualization

    Storage virtualization is the pooling of physical storage from multiple storage devices into what appears to be a single storage ...

Close