Friday, December 27, 2013

Astronomy and a Year

A year (Old English gēar, Gothic jēr, Runic Jēran) is the orbital period of the Earth moving around the Sun. For an observer on the Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic.
In astronomy, the Julian year is a unit of time, defined as 365.25 days of 86400 SI seconds each (no leap seconds).
There is no universally accepted symbol for the year as a unit of time. The International System of Units does not propose one. A common abbreviation in international use is a (for Latin annus), in English also y or yr.
Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, hours of daylight, and consequently vegetation and fertility. In temperate and subpolar regions, generally four seasons are recognized: spring, summer, autumn and winter, astronomically marked by the Sun reaching the points of equinox and solstice, although the climatic seasons lag behind their astronomical markers. In some tropical and subtropical regions it is more common to speak of the rainy (or wet, or monsoon) season versus the dry season.
A calendar year is an approximation of the Earth's orbital period in a given calendar. A calendar year in the Gregorian calendar (as well as in the Julian calendar) has either 365 (common years) or 366 (leap years) days.
So the year is the time it takes for the Earth to go around the Sun, right? Well, not exactly. It depends on what you mean by “year” and how you measure it. This takes a wee bit of explaining, so here is the link than tells you all about the tale of the year.

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