Browse Definitions:
Definition

hour (hr)

The hour (symbolized hr) is a unit of time , equivalent to 3600 second s (s), 60 minute s (min), or 1/24 of a mean solar day (msd). The hour is also used by astronomers as one of two coordinates that define the positions of objects in the sky.

Informally, time is measured according to a scheme that uses two 12-hr segments per mean solar day. The first segment, a.m., begins at midnight and ends at noon. The second segment, p.m., begins at noon and ends at midnight. Time in this format is written in the form h:mm or hh:mm, where h or hh represents the hour from 1 to 12, and mm represents the minute from 00 to 59.

Astronomers, most engineers, aviators, navigators, and military people use a 24-hour time scheme that begins and ends at midnight. In this format, time is denoted in the form hhmm, where hh represents the hour from 00 to 23, and mm represents the minute from 00 to 59.

In celestial coordinates, the hour (hr) is the standard unit of right ascension (RA). Right ascension is measured from west to east along the celestial equator, an imaginary line in the heavens that lies directly over Earth's geographic equator. There are 24 hr of right ascension in a complete circle; therefore 1 hr is the equivalent of 15 angular degree s (15° or 15 deg). The point RA = 0 is the vernal equinox, the position of the Sun in the heavens as it crosses the celestial equator going from south to north. This occurs annually on March 20 or 21.

Also see time , second , angular degree , International System of Units ( SI ), and Table of Physical Units .

This was last updated in March 2011

Start the conversation

Send me notifications when other members comment.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

Powered by:

SearchCompliance

  • PCAOB (Public Company Accounting Oversight Board)

    The Public Company Accounting Oversight Board (PCAOB) is a Congressionally-established nonprofit that assesses audits of public ...

  • cyborg anthropologist

    A cyborg anthropologist is an individual who studies the interaction between humans and technology, observing how technology can ...

  • RegTech

    RegTech, or regulatory technology, is a term used to describe technology that is used to help streamline the process of ...

SearchSecurity

  • Advanced Encryption Standard (AES)

    The Advanced Encryption Standard, or AES, is a symmetric block cipher used by the U.S. government to protect classified ...

  • identity theft

    Identity theft, also known as identity fraud, is a crime in which an imposter obtains key pieces of personally identifiable ...

  • spear phishing

    Spear phishing is an email-spoofing attack that targets a specific organization or individual, seeking unauthorized access to ...

SearchHealthIT

SearchDisasterRecovery

  • call tree

    A call tree -- sometimes referred to as a phone tree -- is a telecommunications chain for notifying specific individuals of an ...

  • mass notification system (MNS)

    A mass notification system is a platform that sends one-way messages to inform employees and the public of an emergency.

  • disaster recovery as a service (DRaaS)

    One approach to a strong disaster recovery plan is DRaaS, where companies offload data replication and restoration ...

SearchStorage

  • CIFS (Common Internet File System)

    CIFS (Common Internet File System) is a protocol that gained popularity around the year 2000, as vendors worked to establish an ...

  • GlusterFS (Gluster File System)

    GlusterFS (Gluster File System) is an open source distributed file system that can scale out in building-block fashion to store ...

  • virtual memory

    Virtual memory is a memory management capability of an OS that allows a computer to compensate for physical memory shortages by ...

SearchSolidStateStorage

  • Tier 0

    Tier 0 (tier zero) is a level of data storage that is faster, and perhaps more expensive, than any other level in the storage ...

  • PCIe SSD (PCIe solid-state drive)

    A PCIe SSD (PCIe solid-state drive) is a high-speed expansion card that attaches a computer to its peripherals.

  • SSD caching

    SSD caching, also known as flash caching, is the temporary storage of data on NAND flash memory chips in a solid-state drive so ...

SearchCloudStorage

  • RESTful API

    A RESTful application program interface breaks down a transaction to create a series of small modules, each of which addresses an...

  • cloud storage infrastructure

    Cloud storage infrastructure is the hardware and software framework that supports the computing requirements of a private or ...

  • Zadara VPSA and ZIOS

    Zadara Storage provides block, file or object storage with varying levels of compute and capacity through its ZIOS and VPSA ...

Close