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  2. Year - Wikipedia

    en.wikipedia.org/wiki/Year

    A calendar year is an approximation of the number of days of the Earth's orbital period, as counted in a given calendar.The Gregorian calendar, or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars.

  3. 360-day calendar - Wikipedia

    en.wikipedia.org/wiki/360-day_calendar

    The 360-day calendar is a method of measuring durations used in financial markets, in computer models, in ancient literature, and in prophetic literary genres.. It is based on merging the three major calendar systems into one complex clock [citation needed], with the 360-day year derived from the average year of the lunar and the solar: (365.2425 (solar) + 354.3829 (lunar))/2 = 719.6254/2 ...

  4. Sunrise equation - Wikipedia

    en.wikipedia.org/wiki/Sunrise_equation

    is the number of days since Jan 1st, 2000 12:00. is the Julian date; 2451545.0 is the equivalent Julian year of Julian days for Jan-01-2000, 12:00:00. 0.0008 is the fractional Julian Day for leap seconds and terrestrial time (TT). TT was set to 32.184 sec lagging TAI on 1 January 1958. By 1972, when the leap second was introduced, 10 sec were ...

  5. Equation of time - Wikipedia

    en.wikipedia.org/wiki/Equation_of_time

    where D is the date, counted in days starting at 1 on 1 January (i.e. the days part of the ordinal date in the year). 9 is the approximate number of days from the December solstice to 31 December. A is the angle the Earth would move on its orbit at its average speed from the December solstice to date D .

  6. Calendrical calculation - Wikipedia

    en.wikipedia.org/wiki/Calendrical_calculation

    The number of days between two dates, which is simply the difference in their Julian day numbers. The dates of moveable holidays, like Christian Easter (the calculation is known as Computus) followed up by Ascension Thursday and Pentecost or Advent Sundays, or the Jewish Passover, for a given year. Converting a date between different calendars.

  7. Earth's orbit - Wikipedia

    en.wikipedia.org/wiki/Earth's_orbit

    One complete orbit takes 365.256 days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi). [2] Ignoring the influence of other Solar System bodies, Earth's orbit, also called Earth's revolution, is an ellipse with the Earth–Sun barycenter as one focus with a current eccentricity of 0.0167. Since this value ...

  8. Sidereal year - Wikipedia

    en.wikipedia.org/wiki/Sidereal_year

    The sidereal year is 20 min 24.5 s longer than the mean tropical year at J2000.0 (365.242 190 402 ephemeris days). [ 1 ] At present, the rate of axial precession corresponds to a period of 25,772 years, [ 3 ] so sidereal year is longer than tropical year by 1,224.5 seconds (20 min 24.5 s, ~365.24219*86400/25772).

  9. Solar longitude - Wikipedia

    en.wikipedia.org/wiki/Solar_longitude

    Solar longitude, commonly abbreviated as Ls, is the ecliptic longitude of the Sun, i.e. the position of the Sun on the celestial sphere along the ecliptic.It is also an effective measure of the position of the Earth (or any other Sun-orbiting body) in its orbit around the Sun, [1] usually taken as zero at the moment of the vernal equinox. [2]