how long is a decades
A decade is a period of 10 years. The word is derived (via French and Latin) from the Ancient Greek: δεκάς, romanized: dekas, which means a group of ten. Decades may describe any ten-year period, such as those of a person's life, or refer to specific groupings of calendar years.
Usage
Any period of ten years is a "decade".[1] For example, the statement that "during his last decade, Mozart explored chromatic harmony to a degree rare at the time" merely refers to the last ten years of Wolfgang Amadeus Mozart's life without regard to which calendar years are encompassed. Also, 'the first decade' of a person's life begins on the day of their birth and ends at the end of their 10th year of life when they have their 10th birthday; the second decade of life starts with their 11th year of life (during which one is typically still referred to as being "10") and ends at the end of their 20th year of life, on their 20th birthday; similarly, the third decade of life, when one is in one's twenties or 20s, starts with the 21st year of life, and so on, with subsequent decades of life similarly described by referencing the tens digit of one's age.
0-to-9 decade
The most widely used method for denominating decades is to group years based on their shared tens digit, from a year ending in a 0 to a year ending in a 9 – for example, the period from 1960 to 1969 is the 1960s, and the period from 1990 to 1999 is the 1990s. Sometimes, only the tens part is mentioned (60s or sixties, and 90s or nineties), although this may leave it ambiguous as to which century is meant. However, this method of grouping decades cannot be applied to the decade immediately preceding AD 10, because there was no year 0.
Particularly in the 20th century, 0-to-9 decades came to be referred to with associated nicknames, such as the "Swinging Sixties" (1960s), the "Warring Forties" (1940s) and the "Roaring Twenties" (1920s). This practice is occasionally also applied to decades of earlier centuries; for example, referencing the 1890s as the "Gay Nineties" or "Naughty Nineties".
Why are the 1900s called the 20th century and the 2000s the 21st century?
How long has our calendar been around?
We are writing this on 12/26/12 or Wednesday, December 26, 2012. Traditionally understood as two-thousand and twelve years (give or take a few) after Jesus Christ is believed to have been born. But if Jesus used a calendar, it would not have been the one we use.
Our calendar is called the Gregorian calendar and was instituted by Pope Gregory XIII in 1582. There are many other calendars. Quite a few societies have used calendars linked to the years their kings ruled. And there are numerous calendars, beyond the Gregorian calendar, that are still in use today. For example, 2012 equates to 1434/35 in the Islamic calendar and 5772-73 in the Jewish calendar (both are lunar, based on the cycles of the moon).
Many people use the abbreviations B.C. and A.D. with a year (for example, A.D. 2012). B.C. refers to "Before Christ," and the initials, A.D., stand for Anno Domini, which is Latin for "In the year of our Lord." This system was devised by a monk in the year 525.
A more recent system uses B.C.E. which stands for "Before the Common Era" and C.E. for "Common Era." This newer system is now widely used as a way of expressing the same periods as B.C. and A.D., but without the Christian reference. According to this system, we count time backwards Before the Common Era (B.C.E.) and forwards in the Common Era (C.E.).
Often dates will be preceded with a "c." or a "ca." These are abbreviations of the Latin word "circa" which means around, or approximately. We use this before a date to indicate that we do not know exactly when something happened, so c. 400 B.C.E. means approximately 400 years Before the Common Era.
Why 2012 is in the 21st Century
We live in the 21st Century, that is, the 2000s. Similarly when we say "20th Century," we are referring to the 1900s. All this because, according to the calendar we use, the 1st Century included the years 1-100 (there was no year zero), and the 2nd Century, the years 101-200. Similarly, when we say 2nd Century B.C.E. we are referring to the years 200-101 B.C.E.
Within our calendar, we also have a tendency to find portentous meaning in the millennial years, that is, in the years 1000 and more recently, 2000.
1-to-0 decade
A rarer approach groups years from the beginning of the AD calendar era to produce successive decades from a year ending in a 1 to a year ending in a 0, with the years 1–10 described as "the 1st decade", years 11–20 "the 2nd decade", and so on; later decades are more usually described as 'the Nth decade of the Mth century' (using the strict interpretation of 'century'). For example, "the second decad of the 12th. Cent." (sic); "The last decade of that century"; "1st decade of the 16th century"; "third decade of the 16th century"; "the first decade of the 18th century". This decade grouping may also be identified explicitly; for example, "1961–1970";[8] "2001–2010"; "2021–2030".[10] The BC calendar era ended with the year 1 BC and the AD calendar era began the following year, AD 1. There was no year 0.
Public usage of the two methods
A YouGov poll was conducted on December 2, 2019, asking 13,582 adults in the United States, "When do you think the next decade will begin and end?" Results showed that 64% answered that "the next decade" would begin on January 1, 2020, and end on December 31, 2029 (0-to-9 method); 17% answered that "the next decade" would begin on January 1, 2021, and end on December 31, 2030 (1-to-0 method); 19% replied that they did not know.
How long is a century?
A century is 100 years.A decade is 10 years.10 years = a Decade,20 years = 2 Decades.30 years = 3 Decades.40 years = 4 Decades.
Alister is not quite right, Yes there are 100 years in a century, but the first year is 1901, and the last 2000…. A Roman Centurion commanded about 100 men, but in reality, a century of Roman soldiers was between 200 and 1000 men… Though Julus Ceasar started to make double-strength units, so a cohort of troops under the Centurion could have as many as 300- 800 troops, and there were several cohorts in each legion. The Latin word for a hundred was Centum… Century was used by the early Christians to count the number of years since Christ's crucifixion.
Horology
Horology ("the study of time", related to Latin horologium from Greek ὡρολόγιον, "instrument for telling the hour", from ὥρα hṓra "hour; time" and -o- interfix and suffix -logy) is the study of the measurement of time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time. In current usage, horology refers mainly to the study of mechanical time-keeping devices, while chronometry more broadly includes electronic devices that have largely supplanted mechanical clocks for the best accuracy and precision in time-keeping.
People interested in horology are called horologists. That term is used both by people who deal professionally with timekeeping apparatus (watchmakers, clockmakers), as well as aficionados and scholars of horology. Horology and horologists have numerous organizations, both professional associations and more scholarly societies. The largest horological membership organization globally is the NAWCC, the National Association of Watch and Clock Collectors, which is USA based, but also has local chapters elsewhere.
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