A System of Dating.

 BC and AD: BC is the acronym of Before Christ. This is an English phrase meaning ‘Before the birth of (Jesus) Christ’. So, the years before the birth of Jesus Christ is known as ‘Before Christ’ and it is denoted as BC in short.
e.g. : Gautama Buddha was born in 563 BC and died in 483 BC. Alexander the Great was born in 365 BC and died in 323 BC.

AD is the acronym of Anno Domini. This is the Latin phrase meaning ‘In the year of Lord (Jesus Christ)’. So, the years beginning with the birth of Jesus Chirst is known as ‘Anno Domini’, and it is denoted as AD in short.
e.g. : Jesus Christ was crucified in 30 AD. Kushana ruler Kanishka ascended the throne in 78 AD. Hazrat Muhammad was born in 570 AD and died in 623 AD.

Time Line: The line displaying the events of past time is called ‘Time Line’.

From the above-mentioned time line, it is clear that the years before the birth of Christ are counted backward, the meaning of one year before 1 BC is 2 BC, the meaning of one year before 2 BC is 3 BC and so on. In other words, firstly the year of 5 BC passed, that 4 BC came, after the 3 BC, after that 2 BC and lastly 1 BC appeared.

From the above-mentioned time line it is also cleared that the year after the birth of Jesus Christ are counted forward. It implies that the meaning of one year after 1 AD is 2 AD, one year after 2 AD is 3 AD and so on, it is like forward counting.

Time Glossary: The glossary relating to time is known as ‘Time Glossary’.

Some important terms associated with time are -----

Decade	The period of 10 years.
First Half (of a century)	First 50 years of a century i.e., the period from 1st year to 50th year.
Second Half (of a century)	Last 50 years of a century i.e., the period from 51st year to 100th year.
Century	The period of 100 years.
Millennium	The period of 1,000 years.
Circa-Ca./C	If the exact date is not known then the word ‘circa’ is used with the date. In short, Circa is used with the date. In short, Circa is denoted as Ca, or C. e.g.: C. 1,500 BC – 600 BC: The Vedic culture Period means that the exact date of Vedic Culture Period is not known but it (C.1500 BC-600 BC) is somewhere close to that.

First decade of 20^th century AD means ---- the period from 1901 AD to 1910 AD.
Fifth decade of 20^th century AD means-----the period from 1941 AD to 1950 AD.
Eighth decade of 20^th century AD means----the period from 1971 AD to 1980 AD.
Last decade of 20^th century AD means-----the period from 1991 AD to 2000 AD.

First half of 20^th Century AD means---- from 1901 AD to 1950 AD.
Second half of 20^th Century AD means--- from 1951 AD to 2000 AD.

6^th Century BC means ---- 600 BC to 501 BC.
4^th Century BC means-----400 BC to 301 BC.
16^th Century AD means----1501 AD to 1600 AD.
20^th Century AD means----1901 AD to 2000 AD.

Second Millennium BC ---- 2000 BC – 1001 BC.
First Millennium BC ------ 1000 BC – 1 BC.
First Millennium AD ----- 1 AD to 1000 AD.
Second Millennium AD ---- 1001 AD to 2000 AD.