In order to both study and navigate the
Earth, it is important to have a system for describing locations
accurately and mathematically. This system must be generally accepted by
everyone, and it must be easy to use and understand.
The
simplest method for describing locations either on a planet, or on any
flat object, is to create a grid. A grid is a series of evenly spaced
imaginary lines that intersect with one another at right angles. One set
of lines are distributed across the globe horizontally, and one set of
lines are distributed vertically.
But
wait a moment. How do we know where the top and bottom of the Earth are?
Think about it. If the Earth is round, what point is the top? Let's
consider a white marble. Where is the top of the marble? No matter which
way you turn it, every side of the marble looks the same. But what
happens when you spin the marble? As the marble spins, or rotates, for a
few moments, there is a clearly defined top that remains pointing
upwards.
Latitude
Latitude
is the angular distance of any object from the equator measured in
degrees. The angular distance from the equator to itself is 0, thus the
latitude at the equator is 0 °. If we move either up or down from the
equator, our distance increases, and so does our angle to it. Eventually
we reach either the North or South Pole. Standing on the these poles,
places us at exactly a 90 ° angle to the equator.
At any location on Earth we can draw a
circle around it, representing every point that is at the same latitude.
If we were to cut the earth in half at the equator and place a large
piece of paper in between the two halves, we would find that both halves
were exactly the same size. As we move either up or down the Earth,
cutting the planet into two pieces produces one large piece and one
small piece. As we approach the poles, the large piece gets very big,
while the small piece becomes much smaller. Drawing these imaginary
lines at different latitudes produces what we call parallels. Although
technically it is possible to draw an infinite number of parallels at
any number of latitudes, there are a few which are important for you to
understand as you study our planet.
The
first of these is called the equator. The equator is located at 0 °
latitude. Going north from the equator we find the Tropic of Cancer.
This parallel is located at 23.5 ° north. Continuing further northward
we reach the Arctic Circle at 66.5 ° north. Continuing all the way to
the top of the Earth at 90 ° latitude we encounter the North Pole. If we
journey southward from the equator we will find the Tropic of Capricorn
at 23.5 ° south. Continuing south we reach the Antarctic Circle at 66.5
° south. Finally, at 90 ° south, we find the South Pole.
Longitude
As we
have already read, the lines extending around the Earth horizontally
are called lines of latitude. They measure how far north or south an
object is on the Earth. The lines running vertically around the Earth
are called longitude. These lines are called meridians, and measure how
far east or west an object is.
As with latitude, longitude is measured
as an angular distance. With latitude, the angular distance is measured
from the equator. This is a natural place to begin. However, with
longitude there is no natural beginning point. One of these lines must
be designated as a prime meridian, or as the 0 ° mark, but which one?
For many years, each country had its own prime meridian. France used a
meridian passing through Paris, while England used a meridian passing
through Greenwich, England. Either one worked just as well, as long as
you were only communicating with people from the same country. But what
happens as technologies improve, and travelers begin interacting with
people from many different lands? If each country is using a different
prime meridian to mark 0 ° longitude, then it would be impossible to
give someone from another country a location, and have them be able to
accurately find it.
Over
time, more and more travelers began to recognize the meridian passing
through Greenwich, England, as the Prime Meridian. In 1884, a group of
scientists, navigators, and businessmen made Greenwich, England, the
official worldwide Prime Meridian.
The
further away from the Prime Meridian that one travels the higher their
longitude becomes, until they reach 180 ° longitude. If an individual is
in the Eastern Hemisphere, their longitude is measured in degrees east.
If they are in the Western Hemisphere, their longitude is measured in
degrees west.
Plotting Your Location
Using
longitude and latitude, it is now possible to accurately describe any
location on the Earth within a correct distance of only a few inches.
Your home or school probably has a street address. Perhaps it looks
something like 6088 Garden Gate Drive. These numbers tell the mailman
where to deliver your mail, and visitors how to find you. While physical
addresses are very useful, longitude and latitude are more concise and
accurate. A physical address is based on a local system, understood and
accepted only by a small community. Longitude and latitude are accepted
worldwide by the entirety of humanity. If you know your longitude and
latitude, you can tell a distant pen pal exactly where you are on this
sphere-shaped planet.
For hundreds of years, calculating your
longitude and latitude was a somewhat difficult process. Using
specialized tools and the stars as a guide, trained experts could
determine their location, and make sure that their travels were still on
course. However, due to the limits of their equipment, these
measurements were only approximate.
Today,
anyone can quickly and accurately measure their location on the Earth.
One popular method for determining the latitude and longitude of an
object is through the use of Global Positioning Satellites, or GPS.
Inexpensive GPS devices use the signals from satellites orbiting the
Earth to calculate the exact location of the person holding the device.
Many of these devices also allow the user to save their favorite
locations in a small computer so that these locations can quickly be
found in the future.