Elenco Night’n Day® User Manual
Page 10
17
18
HOUR
An hour is 1/24
th
of a day or 60 minutes long. In an hour, the Earth turns 15º in
longitude. Each 15º segment is one time zone.
LATITUDE
The angular distance of a
location from the equator
to the North or South
Pole. The equator has
latitude = 0º. The North
Pole has latitude = +90º
and the South Pole is at
–90º. A point halfway
between the equator and
the North Pole has
latitude of +45º.
LONGITUDE
The angular distance east or west from the zero longitude meridian (at
Greenwich). Longitude goes from 0º to +180º as one heads east of Greenwich,
and 0º to –180º going west of Greenwich.
Meridians
Half circles that go around the Earth drawn from pole to pole. There are 24
meridians, and the spaces between them are the hourly time zones.
The meridian at Greenwich (0º longitude) is called the Prime Meridian.
The meridian at 180º is the International Date Line.
PARALLELS
Circles drawn around the Earth parallel to the equator. Parallels represent lines of
latitude. The parallel at Beijing is at latitude +40ºand goes around the Earth north of
and parallel to the equator. The parallel at Jakarta is at latitude of –6º and is drawn
parallel to and south of the equator.
POLAR CIRCLES
The parallels at latitude +66.5º and –66.5º are the Arctic and Antarctic Circles.
Areas north of the Arctic Circle experience 24-hour daylight in summer and 24-hour
night in winter. Areas south of the Antarctic Circle also see 24-hour day and night in
their respective summer and winter seasons.
SOLSTICE
The time of year when the Earth is at its maximum inclination toward or away from the
Sun. Each hemisphere has a summer solstice (tipped toward) and winter solstice (tipped
away). These occur on June 22
nd
– 23
rd
and December 22
nd
– 23
rd
. June 22
nd
– 23
rd
is the
first day of summer in the northern hemisphere, and the first day of winter in the
southern hemisphere. December 22
nd
– 23
rd
is the first day of winter in the north and
first day of summer in the south.
SUBSOLAR POINT
Point on the Earth where the Sun is shining directly overhead. This is also the point on
the Earth directly in line with the Sun and the center of the Earth. Only locations on the
Earth between latitude +23.5º and –23.5º can have the Sun directly overhead.
TIME ZONE
The segment between two meridians separated by 15º. For example, from 0º (Prime
Meridian) to +15º longitude is the first time zone. Each of these segments is 1/24 of the
Earth’s circumference, hence each represents a one hour time zone.
TROPICS
Area on Earth between the two parallels at latitude +23.5º and –23.5º. The northern
tropic is the Tropic of Cancer and the southern is the Tropic of Capricorn. The tropics
region is the only place where the Sun can be directly overhead during the year.
YEAR
The time for the Earth to orbit the Sun once, or to make one complete revolution
around the Sun. The year = 365.2425 days or 365 days and 5.8 hours. Since the year is
not an even 365 days, the extra 5.8 hours add up to almost one day after four years.
That is the origin of a leap year of 366 days.
December 22
nd
– June 23
rd
: Summer
begins in the southern hemisphere when
the Sun is directly over the Tropic of
Capricorn. The northern hemisphere
begins winter and has the shortest
daylight period.
June 22
nd
– June 23
rd
: Summer begins in
the northern hemisphere when the Sun is
directly over the Tropic of Cancer. The
northern hemisphere now gets more
sunlight than at any other time of year.
At this time, the southern hemisphere
has its first day of winter.
Latitude 60º N
Latitude 30º N
Latitude 30º S
Greenwich
meridian
60º E
30º E
30º O
60º O
Equinox
Earth Axis
Sun r
ay
s
Arctic Circle
Tropic of Cancer
Equator
Tropic of Capricorn
Antarctic Circle
Earth Axis
Sun r
ay
s
Arctic Circle
Tropic of Cancer
Equator
Tropic of Capricorn
Antarctic Circle