called the area Mesopotamia. The name
means “land between the rivers.” Several
ancient cities were built along the Tigris.
One was Assur. That city gave its name
to the empire called Assyria. Nineveh
was another ancient city on the river. It
was Assyria’s capital. The main modern
cities on the Tigris are Baghdad and
Mosul, both in Iraq.
#More to explore
Euphrates River • Irrigation
• Mesopotamia
Tile
#see Brick and Tile.
Time
People use the idea of time to measure
how long it takes for things to happen.
They also use time to describe how long
ago things happened in the past. Time
helps to describe when things may happen
in the future as well.
66 Tigris River BRITANNICA STUDENT ENCYCLOPEDIA
Units of Time
People divide time into days and hours.
There are 24 hours in one full day and
night. Hours are divided into minutes
and seconds. There are 60 minutes in an
hour and 60 seconds in a minute.
People measure longer periods of time by
years. There are 365 or 366 days in one
year. A year is divided into 12 months.
Months have from 28 to 31 days.
Time Zones
At any time, only part of Earth experiences
daylight. It is nighttime for the
rest of the planet. This means that it
cannot be the same time of day in every
part of the world. For this reason people
have divided the globe into 24 sections
called time zones. At most places inside
a time zone, it is the same time of day.
Imaginary lines separate all the time
zones. The lines run from the North
Pole to the South Pole. The first time
zone begins at 0° longitude, or the
prime meridian. This imaginary line
runs through Greenwich, England.
When people cross one of the imaginary
lines, they enter a new time zone. The
time of day changes by one hour. If they
cross into a time zone to the west, it is
one hour earlier. If they cross into a time
zone to the east, it is one hour later. (In
a few places in the world, the time
changes by only a half hour.)
The imaginary lines dividing the time
zones are not always straight. They often
bend west or east. This allows whole
countries or regions to be within a single
time zone. However, large countries—
such as the United States and Russia—
are divided into several time zones.
On the other side of Earth from the
prime meridian is the International Date
Line (IDL). It runs through the Pacific
Ocean at about 180° longitude. When
travelers cross the IDL going from west
to east, they gain a whole day on the
calendar. For example, if they start traveling
on January 2, the date changes to
January 1 when they cross the IDL.
When people travel from east to west
across the IDL, they move a day forward
in time.
History
Ancient people measured time by looking
at the sky. They saw the sun rise and
set and the Moon grow full. They
watched the stars and the other planets
change position. They also experienced
the days becoming shorter and longer
and the cycle of the seasons.
A stopwatch measures the minutes and seconds
an athlete takes to complete a run.
People use many different types of watches,
clocks, and calendars to keep track of time.
BRITANNICA STUDENT ENCYCLOPEDIA Time 67
Earth is divided into 24 time zones. The boundary lines between the zones are not always straight because every country makes its own rules
about which time zones it wants to be in.
68 Time BRITANNICA STUDENT ENCYCLOPEDIA
People in ancient Egypt, Mesopotamia,
Central America, and other places created
calendars to keep track of the passing
days. The ancient Egyptians also
invented a form of clock called a sundial.
Sundials cast shadows that move as
the day passes.
Eventually people all over the world
had developed many types of clocks
and calendars to keep track of time. But
the time was different in every city. In
the 1800s some people thought there
should be one system of measuring
time so that everyone could agree about
what time it is. This was important for
such things as making schedules for
trains and knowing when to go to
school. In 1884 countries throughout
the world adopted the time zone system
that is still in use.
#More to explore
Calendar • Clock • Latitude and
Longitude • Season • Sundial
Tirane
Population
(2001 census)
343,078
Tirane is the capital of Albania, a
country in southeastern Europe. It lies
on the Ishm River. It is Albania’s largest
city.
Tirane is Albania’s main center of business
and industry. However, in the early
21st century the country’s economy was
one of the poorest in Europe. Factories
in Tirane make clothing, processed
foods, leather, and other products.
ATurkish general foundedTirane in the
early 1600s. Albania was then part of the
TurkishOttoman Empire.Tirane
gradually grew into a busy trading center.
Albania became an independent country
in 1912. Tirane became its capital in
1920. Between 1939 and 1944, during
WorldWar II, Italian and then German
forces controlled the city.
Between 1946 and the early 1990s,
Albania was a Communist country. Protests
in Tirane helped to bring an end to
Communist rule. However, the end of
Communism did not bring about a lasting
peace. In the later 1990s the city was
the site of several violent political protests.
#More to explore
Albania
