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
SearchNetworking
  • network packet

    A network packet is a basic unit of data that's grouped together and transferred over a computer network, typically a ...

  • virtual network functions (VNFs)

    Virtual network functions (VNFs) are virtualized tasks formerly carried out by proprietary, dedicated hardware.

  • network functions virtualization (NFV)

    Network functions virtualization (NFV) is a network architecture model designed to virtualize network services that have ...

SearchSecurity
SearchCIO
SearchHRSoftware
  • recruitment

    Recruitment is the process of finding, screening, hiring and eventually onboarding qualified job candidates.

  • recruitment management system

    A recruitment management system (RMS) is a set of tools designed to manage the recruiting process.

  • applicant tracking system (ATS)

    An applicant tracking system (ATS) is software that manages the recruiting and hiring process, including job postings and job ...

SearchCustomerExperience
  • data clean room

    A data clean room is a technology service that helps content platforms keep first person user data private when interacting with ...

  • recommerce

    Recommerce is the selling of previously owned items through online marketplaces to buyers who reuse, recycle or resell them.

  • implementation

    Implementation is the execution or practice of a plan, a method or any design, idea, model, specification, standard or policy for...

Close