THE
YEAR AD 2000
Produced
by the Information Services Department of the Royal
Greenwich Observatory.
The
year AD 2000 will be a notable one. Many people are asking the questions,
`Will 2000 be a
leapyear?' and `Will
it be the start of the new millennium?'
LeapYears.
Leapyears
were introduced into the calendar by Julius Caesar. They
are necessary as the length of the year is not an integral
number of days. The Julian calendar uses the fact that the
length of the year is close to 365 and a quarter days.
So a basic year with 365 days with an additional extra day
every fourth year will give a good approximation.
This
calendar was used until the 16th century when
the small discrepancy between the approximate length of the
year, 365.25 days,
and the true length, 365.24219 days,
added up to several days. Pope
Gregory realised that this meant that
the date of Easter would eventually
not fall in the spring but would become closer and closer
to Dec 25, Christmas.
In
1582 the Gregorian
calendar was instituted. It changed the rule
for determining whether a year should be a leapyear by stating
that century years should only be leap years
if they were divisible by 400.
The effect of this is to make the adopted average yearlength 365.2425
days, an approximation that will only
amount to one day's error after 4000
years.
Britain
adopted the Gregorian calendar in 1752 when september 2nd was
followed by September 14th.
We
still use the Gregorian calendar and so the year 2000, which is divisible
by 400, will be a leapyear.
Millennia.
A
millennium is a period of 1000 years. The question of which year
is the first year of the millennium hinges on the date
of the first year AD.
Unfortunately
the sequence of years going from BC to AD does
not include a Year 0. The
sequence of years runs 3 BC, 2 BC, 1 BC, AD 1, AD 2, AD 3 etc. This
means that the first year of the first millennium
was 1 AD. The one thousandth year was AD 1000 and the first day of
the second millennium was AD 1001.
It
is thus clear that the start of the new millennium will be 1 Jan
2001.
Celebrations.
The
year AD 2000 will certainly be celebrated, as is natural for a year
with such a round number but, accurately speaking, we
will be celebrating the 2000th year or the last year
of the millennium, not the start of the new millennium.
Whether this will be an excuse for more celebrations in the following year
will have to be seen!
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