Sidereal time

Sidereal time /sˈdɪəriəl/ is a time-keeping system astronomers use to keep track of the direction to point their telescopes to view a given star in the night sky. Briefly, sidereal time is a "time scale that is based on the Earth's rate of rotation measured relative to the fixed stars" rather than the Sun.

From a given observation point, a star found at one location in the sky will be found at nearly the same location on another night at the same sidereal time. This is similar to how the time kept by a sundial can be used to find the location of the Sun. Just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of the Earth, so do the stars. Both solar time and sidereal time make use of the regularity of the Earth's rotation about its polar axis, solar time following the Sun while sidereal time roughly follows the stars. More exactly, sidereal time is the angle, measured from the observer's meridian, along the celestial equator, to the great circle that passes through the March equinox and both poles, and is usually expressed in hours, minutes, and seconds. Common time on a typical clock measures a slightly longer cycle, accounting not only for the Earth's axial rotation but also for the Earth's annual revolution around the Sun of slightly less than 1 degree per day (in fact to the nearest arc-second, it takes 365.2422 days to revolve therefore 360 degrees/365.2422 days = 0.9856 degrees or 59 arc-minutes, 8 arc-seconds per day, i.e., slightly less than 1 degree per day).

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Not a do or die moment: Despite failed merger, Bluffton University remains financially stable

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Relief on the way for Sydney drivers amid major freeway upgrade

Sydney Morning Herald 03 Mar 2025
A quarter of a million Sydney-siders have been caught in the confusion of the Warringah Freeway Upgrade every day, and drivers have just endured the most challenging part of the works ....
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