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The Julian date (JD) of any instant is the Julian day number plus the fraction of a day since the preceding noon in Universal Time. Julian dates are expressed as a Julian day number with a decimal fraction added. [ 8] For example, the Julian Date for 00:30:00.0 UT January 1, 2013, is 2 456 293.520 833. [ 9]
A plot of hours of daylight as a function of the date for changing latitudes. This plot was created using the simple sunrise equation, approximating the sun as a single point and does not take into account effects caused by the atmosphere or the diameter of the Sun. The sunrise equation or sunset equation can be used to derive the time of ...
Animation showing the difference between a sidereal day and a solar day. Sidereal time ("sidereal" pronounced / saɪˈdɪəriəl, sə -/ sy-DEER-ee-əl, sə-) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky.
The United States Naval Observatory states "the Equation of Time is the difference apparent solar time minus mean solar time ", i.e. if the sun is ahead of the clock the sign is positive, and if the clock is ahead of the sun the sign is negative. [6] [7] The equation of time is shown in the upper graph above for a period of slightly more than a ...
ISO 8601 is an international standard covering the worldwide exchange and communication of date and time -related data. It is maintained by the International Organization for Standardization (ISO) and was first published in 1988, with updates in 1991, 2000, 2004, and 2019, and an amendment in 2022. [1] The standard provides a well-defined ...
On a prograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the Sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 = one sidereal day). But it is not until a little later, at time 3, that the Sun is overhead again (1→3 = one solar day). More simply, 1→2 is a complete ...
In traditional American usage, dates are written in the month–day–year order (e.g. August 11, 2024) with a comma before and after the year if it is not at the end of a sentence [ 2] and time in 12-hour notation (4:06 am). International date and time formats typically follow the ISO 8601 format (2024-08-11) for all-numeric dates, [ 3] write ...
The smallest meaningful increment of time is the Planck time―the time light takes to traverse the Planck distance, many decimal orders of magnitude smaller than a second. [ 1 ] The largest realized amount of time, based on known scientific data, is the age of the universe , about 13.8 billion years—the time since the Big Bang as measured in ...