Year Guide, Meaning , Facts, Information and Description
A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. By extension, this can be applied to any planet: for example, "Martian year".
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2 Calendar year 3 Astronomical year 4 Variation in the length of the year and the day 5 See also |
Calendars usually aim to predict the seasons, but because it is hard to determine the length of the seasonal year, they instead use an astronomical year as a surrogate for the seasonal year. For example, the ancient Egyptians used the heliacal rising of Sirius to predict the flooding of the Nile.
The Gregorian calendar aims to keep the vernal equinox on or close to March 21; hence it follows the vernal equinox tropical year.
No astronomical year has an integer number of days, so any calendar that follows an astronomical year must have a system of intercalation such as leap years.
A Julian year is exactly 365.25 days, the average length of the year in the Julian calendar. It is still used in ephemerides because of the very simple conversion between Julian dates and Julian years: 100 Julian years is just another way of saying 36525 days.
The sidereal year is the time for the Earth to complete one revolution of its orbit, as measured in a fixed frame of reference (such as the fixed stars, Latin sidus). Its duration is on average:
Seasonal year
A seasonal year is the time between successive recurrences of a seasonal event such as the flooding of a river, the migration of a species of bird, or the flowering of a species of plant.Calendar year
A calendar year is the time between two dates with the same name in a calendar.Astronomical year
An astronomical year is the time between two recurrences of an astronomical event.
The anomalistic year is the time for the Earth to complete one revolution with respect to its apsides. The orbit of the Earth is elliptical; the extreme points, called apsides, are the perihelion, where the Earth is closest to the Sun (January 2 in 2000), and the aphelion, where the Earth is furthest from the Sun (July 2 in 2000). Because of gravitational disturbances by the other planets, the shape and orientation of the orbit are not fixed, and the apsides slowly move with respect to a fixed frame of reference. Therefore the anomalistic year is slightly longer than the sidereal year. It is also longer than the tropical year (the basis of Gregorian calendar) and so the date of perihelion gradually advance every year. It takes 21.000 years to make a complete cycle of dates.
The average duration of the anomalistic year is:
- 365.259635864 days (365d 6h 13m 52s) (at the epoch J2000.0).
- 346.620075883 days (346d 14h 52m 54s) (at the epoch J2000.0).
- 411.78443029 days (411d 18h 49m 34s) (at the epoch J2000.0).
The Sothic year is the interval between the heliacal risings of the star Sirius. Its duration is very close to the mean Julian calendar year of 365.25 days.
The Gaussian year is the sidereal year for an ideal planet governed by the Gaussian gravitational constant. Its length is:
- 365.2568983 days (365d 6h 9m 56s).
- B = 2000 + (JD - 2451544.53)/365.242189
This is an Article on Year. Page Contains Information, Facts Details or Explanation Guide About Year Variation in the length of the year and the day
The exact length of a year changes over time. The main sources of this change are as follows:
Tidal drag between the Earth and the Moon and Sun increases the length of the day and of the month. This in turn depends on factors such as continental rebound and sea level rise.
See also