Calender 2013 Wallpapers

Calender 2013 - photo wallpapers: [br]A calendar is a system of organising days for a socially, religious, [br]commercially or administratively useful purpose. This organisation is [br]done by giving names to periods of time - typically days, weeks, months [br]and years. The name given to each day is known as a date. Periods in a [br]calendar (such as years and months) are usually, though not [br]necessarily, synchronised with the cycles of some astronomical [br]phenomenon, such as the cycle of the sun, or the moon. Many [br]civilisations and societies have devised a calendar, usually derived [br]from other calendars on which they model their systems, suited to their [br]particular needs.[br] [br] [br]A calendar is also a physical device (often paper). This is the most [br]common usage of the word. Other similar types of calendars can include [br]computerised systems, which can be set to remind the user of upcoming [br]events and appointments. As a subset, 'calendar' is also used to denote [br]a list of particular set of planned events (for example, court [br]calendar).[br] [br] [br]Days used by solar calendars: [br]Solar calendars assign a date to each solar day. A day may consist of [br]the period between sunrise and sunset, with a following period of [br]night, or it may be a period between successive events such as two [br]sunsets. The length of the interval between two such successive events [br]may be allowed to vary slightly during the year, or it may be averaged [br]into a mean solar day. Other types of calendar may also use a solar day.[br] [br] [br]Calendar reform: There have [br]been a number of proposals for reform of the calendar, such as the [br]World Calendar, International Fixed Calendar and Holocene calendar. The [br]United Nations considered adopting such a reformed calendar for a while [br]in the 1950s, but these proposals have lost most of their popularity.[br] [br] [br]Lunar calendar: Not all [br]calendars use the solar year as a unit. A lunar calendar is one in [br]which days are numbered within each lunar phase cycle. Because the [br]length of the lunar month is not an even fraction of the length of the [br]tropical year, a purely lunar calendar quickly drifts against the [br]seasons. It does, however, stay constant with respect to other [br]phenomena, notably tides. A lunisolar calendar is a lunar calendar that [br]compensates by adding an extra month as needed to realign the months [br]with the seasons. An example is the Jewish calendar which uses a 19 [br]year cycle. Lunar calendars are believed to be the oldest calendars [br]invented by mankind. Cro-Magnon people are claimed to have invented one [br]around 32,000 BC.[br]

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