:max_bytes(150000):strip_icc():format(webp)/Mens-International-Shoe-Sizes-56a866393df78cf7729df94d.jpg)
The Prime Meridian
Establishing
Global Time and Space
by Matt
Rosenberg
The Prime
Meridian is the universally decided zero longitude, an
imaginary north/south line which bisects the world into two and begins the
universal day.
The line starts at the north
pole, passes across the Royal Observatory in Greenwich, England, and ends at
the south pole.
Its existence is purely
abstract, but it is a globally-unifying line that makes the measurement of time
(clocks) and space (maps) consistent across our planet.
The Greenwich line was established in 1884 at the International Meridian
Conference, held in Washington DC.
That conference's main
resolutions were: there was to be a single meridian; it was to cross at
Greenwich; there was to be a universal day, and that day would start at mean
midnight at the initial meridian.
From that moment, the space
and time on our globe have been universally coordinated.
Having
a single prime meridian brings to the world's cartographers a universal map
language allowing them to join their maps together, facilitating international
trade and maritime navigation.
At the same time, the world
now had one matching chronology, a reference by which today you can tell what
time of day it is anywhere in the world simply by knowing its longitude.
Latitudes and Longitudes
Mapping
the entire globe was an ambitious task for people without satellites.
In the case of latitude, the
choice was easy. Sailors and scientists set the zero latitude plane of the earth
through its circumference at the equator and then divided the world from the
equator to the north and south poles into ninety degrees.
All other degrees of latitude
are actual degrees between zero and ninety based on the arc from the plane
along the equator. Imagine a protractor with the equator at zero degrees and
the north pole at ninety degrees.
However, for longitude, which could just as easily use the same measuring
methodology, there is no logical starting plane or place.
The 1884 conference
essentially picked that starting place. Naturally, this ambitious (and highly
politicized) stroke had its roots in antiquity, with the creation of domestic
meridians, which first allowed local mapmakers a way to order their own known
worlds.
The Ancient World
The
classical Greeks were the first to attempt to create domestic meridians.
Although there is some
uncertainty, the most likely inventor was the Greek mathematician and
geographer Eratosthenes (276–194 BCE).
Unfortunately, his original
works are lost, but they are quoted in the Greco-Roman historian Strabo's (63
BCE–23 CE) Geography.
Eratosthenes chose a line on
his maps marking the zero longitude as one that intersected with Alexandria
(his birthplace) to act as his starting place.
The Greeks were not the only ones to invent the meridian concept of course.
Sixth-century Islamic
authorities used several meridians; the ancient Indians picked Sri Lanka;
beginning in the mid-second century CE, south Asia used the observatory at
Ujjain in Madhya Pradesh, India.
The Arabs picked a locality
called Jamagird or Kangdiz; in China, it was at Beijing; in Japan at Kyoto.
Each country picked a domestic
meridian that made sense of their own maps.
Setting West and East
The
invention of the first comprehensive use of geographic coordinates — joining an
expanding world into one map — belongs to the Roman scholar Ptolemy (CE
100-170).
Ptolemy set his zero
longitude on the chain of the Canary Islands, the land he was aware of that was
the furthest west of his known world. All of Ptolemy's world he mapped would be
east of that point.
The
majority of later mapmakers, including the Islamic scientists, followed
Ptolemy's lead.
But it was the voyages of
discovery of the 15th and 16th centuries — not just Europe's of course — which
established the importance and difficulties of having a unified map for
navigation, eventually leading to the 1884 conference.
On most maps which plot the
entire world today, the mid-point center marking the face of the world is still
the Canary Islands, even if the zero longitude is in the UK, and even if the
definition of the "west" includes the Americas today.
Seeing the World as a Unified Globe
By
the mid 19th century there were at least 29 different domestic meridians in
place, and international trade and politics were global, and the need for a
coherent global map became acute.
A prime meridian isn't just a
line drawn on a map as 0 degrees longitude; it is also one that uses a specific
astronomical observatory to publish a celestial calendar that sailors could use
to identify where they were on the planet's surface by using the predicted
positions of the stars and planets.
Each
developing state had its own astronomers and own their own fixed points, but if
the world was to progress in science and international trade, there needed to
be a single meridian, an absolute astronomical mapping shared by the whole
planet.
Establishing a Prime Mapping System
During
the late 19th century, the United Kingdom was both the major colonial power and
a major navigational power in the world.
Their maps and navigational
charts with the prime meridian passing through Greenwich were promulgated and
many other countries adopted Greenwich as their prime meridians.
By
1884, international travel was commonplace and the need for a standardized
prime meridian became readily apparent.
Forty-one delegates from
twenty-five "nations" met in Washington for a conference to
establish zero degrees longitude and the prime meridian.
Why Greenwich?
Even
though the most commonly used meridian at the time was Greenwich, not everyone
was happy with the decision.
The Americas, in particular,
referred to Greenwich as a "dingy London suburb" and Berlin, Parsi,
Washington DC, Jerusalem, Rome, Oslo, New Orleans, Mecca, Madrid, Kyoto, St.
Paul's Cathedral in London, and the Pyramid of Giza, were all proposed as
potential starting places by 1884.
Greenwich
was selected as the prime meridian by a vote of twenty-two in favor, one
against (Haiti), and two abstentions (France and Brazil).
Time Zones
With
the establishment of the prime meridian and zero degrees longitude at
Greenwich, the conference also established time zones.
By establishing the prime
meridian and zero degrees longitude in Greenwich, the world was then divided
into 24 time zones (since the earth takes 24 hours to
revolve on its axis) and thus each time zone was established every fifteen
degrees of longitude, for a total of 360 degrees in a circle.
The
establishment of the prime meridian in Greenwich in 1884 permanently
established the system of latitude and longitude and time zones that we use to
this day.
Latitude and longitude are
used in GPS and is the primary coordinate system for navigation on
the planet.
Matt Rosenberg
· Award-winning
professional geographer
· Author of
two books on geography
Experience
Matt Rosenberg is a former writer for ThoughtCo.
He covered geography for ThoughtCo and About.com for over 20 years. He was an
adjunct professor of geography at California State University,
Sacramento, a city planning and GIS intern for local government, and is a
former newspaper columnist.
Rosenberg has been featured on PBS and NPR, and
he has conducted many interviews about geographical topics for television,
radio, and newspapers. He was director of emergency services for the American
Red Cross and served on more than two dozen major disaster relief operations
around the United States. He has traveled widely across North America and has
visited or studied in Europe, Asia, Africa, and the Middle East. He is a member
of the Association of American Geographers and the National
Council for Geographic Education.
Education
Matt Rosenberg holds a bachelor's degree in
geography from the University of California, Davis and a master's
degree in geography from California State University, Northridge.
Publications
Awards
· Excellence in Media Award, National Council for Geographic
Education, October 2006
ThoughtCo and Dotdash
ThoughtCo is a
premier reference site focusing on expert-created education content. We are one
of the top-10 information sites in the world as rated by comScore, a leading
Internet measurement company. Every month, more than 13 million readers seek
answers to their questions on ThoughtCo.
For more than 20 years, Dotdash brands
have been helping people find answers, solve problems, and get inspired. We are
one of the top-20 largest content publishers on the Internet according to
comScore, and reach more than 30% of the U.S. population monthly. Our brands
collectively have won more than 20 industry awards in the last year alone, and
recently Dotdash was named Publisher of the Year by Digiday, a leading industry
publication.https://www.thoughtco.com/what-is-the-prime-meridian-1435653
No comments:
Post a Comment