Finding Points on a Globe
Now that we understand the shape and size of our planet, let's consider the
difficult challenge of measuring and describing points thereon. How, for
example, do we tell someone who lives on the other side of the Earth where
another object is located? Suppose that we are in an unfamiliar land and we
need to find a distant but important object that is hidden somewhere else on
the Earth. If we just start walking in a random direction, are we likely to find
the hidden object?
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.
Because the Earth is rotating around an imaginary axis, we can define a top
and bottom. We call these the poles. Having a top and bottom of the Earth
allows us to then draw the imaginary lines that we need for our grid. The
lines that extend from pole to pole are called longitude, while the lines that
circle the globe horizontally are referred to as latitude.
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.
Do you want to visit a hidden waterfall in the middle of the vast Utah desert?
You could get directions from the locals, but chances are high that you will
get lost. In the desert, everything looks pretty much the same. How do you
know that you going in the right direction? Using GPS as your guide, you can
rest assured that you are not going to get lost. Look up the exact longitude
and latitude of the waterfall, either online or in a book. These coordinates
can then be entered into the device, which can then be used to guide you to
the exact spot where the waterfall is hidden. These advances in technology
make traveling much easier today than it was in the past.