Geoscience Reference
In-Depth Information
Fig. 2
The location of the Méridienne Verte is marked by the side of the road on Route
Nationale 152 near Manchecourt opposite to a stone obelisk erected to mark the position of
the meridian of 1748 measured by César-François Cassini. Manchecourt is a village between
Malesherbes and Pithiviers, south of Fontainebleau. There are few trees actually planted in this
area to implement the Green Meridian concept! Photo by the author
Hexagon, making the Paris Meridian plain to see. From time to time as one travels
on French highways across the Paris Meridian he or she will see by the side of the
road a notice calling attention to the Méridienne Verte (
Fig. 2
).
WHAT WAS the reason for the choice of the location for the picnic and the trees?
What is the significance of the axis of the Hexagon? What
is
the Paris Meridian?
On Earth every point is defined by two quantities - its latitude and its longitude.
These are angles measured in degrees on Earth's near-spherical surface as seen from its
center. If one knows the latitude and longitude to accuractly to 1 arc minute (1/60
degree), then one knows where he or she is to about 1 nautical mile (about 2 km).
Latitude is defined relative to the Earth's equator, in degrees north and south. Longitude
is measured in degrees west or east of a north-south line on the Earth's surface that
passes through both poles, but there is no natural line that is the zero point.
In order to help their ships navigate across the sea and to measure where they
were in latitude and longitude, the maritime nations of the seventeenth to nineteenth
centuries individually set up such lines through astronomical observation. Even
landlocked countries set up meridians to help locate their cities and towns in latitude
and longitude, although the need to define where the cities are in those terms is not
so pressing. However, there is certainly a strong bureaucratic need to define areas
