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  2. Sidereal time - Wikipedia

    en.wikipedia.org/wiki/Sidereal_time

    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.

  3. Date and time representation by country - Wikipedia

    en.wikipedia.org/wiki/Date_and_time...

    ISO 8601. International standard ISO 8601 (Representation of dates and times) defines unambiguous written all-numeric big-endian formats for dates, such as 2022-12-31 for 31 December 2022, and time, such as 23:59:58 for 23 hours, 59 minutes, and 58 seconds. These standard notations have been adopted by many countries as a national standard, e.g ...

  4. Julian day - Wikipedia

    en.wikipedia.org/wiki/Julian_day

    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]

  5. Old Style and New Style dates - Wikipedia

    en.wikipedia.org/wiki/Old_Style_and_New_Style_dates

    The issue spans the changeover; the date heading reads: "From Tuesday September 1, O.S. to Saturday September 16, N.S. 1752". [1] Old Style (O.S.) and New Style (N.S.) indicate dating systems before and after a calendar change, respectively. Usually, they refer to the change from the Julian calendar to the Gregorian calendar as enacted in ...

  6. Conversion between Julian and Gregorian calendars - Wikipedia

    en.wikipedia.org/wiki/Conversion_between_Julian...

    No guidance is provided about conversion of dates before March 5, -500, or after February 29, 2100 (both being Julian dates). For unlisted dates, find the date in the table closest to, but earlier than, the date to be converted. Be sure to use the correct column. If converting from Julian to Gregorian, add the number from the "Difference" column.

  7. International Date Line - Wikipedia

    en.wikipedia.org/wiki/International_Date_Line

    The International Date Line (IDL) is the line between the South and North Poles that is the boundary between one calendar day and the next. It passes through the Pacific Ocean, roughly following the 180.0° line of longitude and deviating to pass around some territories and island groups. Crossing the date line eastbound decreases the date by ...

  8. ISO 8601 - Wikipedia

    en.wikipedia.org/wiki/ISO_8601

    Ordinal date. 2024‐263. 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]

  9. List of UTC offsets - Wikipedia

    en.wikipedia.org/wiki/List_of_UTC_offsets

    This is a list of the UTC time offsets, showing the difference in hours and minutes from Coordinated Universal Time (UTC), from the westernmost (−12:00) to the easternmost (+14:00). It includes countries and regions that observe them during standard time or year-round. The main purpose of this page is to list the current standard time offsets ...