of the loan becomes less and less. That is why the homeowner pays a great deal toward
interest and not the principal for the first several years of a home mortgage.
For example, if a mortgage is taken out for $100,000 at 6.5 percent for 30 years,
the fixed monthly principal and interest payment is $632.07. For the first month, the
homeowner pays interest on the $100,000 (or $541.67), with the remainder of the pay-
ment ($90.40) going toward principal. In other words, the debt on the principal is
reduced by $90.40. By the next month, the homeowner owes interest on a lesser
amount of money—on $99,909.60 (or $100,000 $90.40), not the $100,000, with
$541.18 going toward interest and $90.89 going toward principal. As payments are
made month after month, the interest decreases and the principal reduction increas-
es. By the 360th payment (or 30 years later), the payment contributes $3.41 to interest
and $628.66 to principal.
MATH AND TRAVELING
How are positions on Earthdetermined?
Positions on Earth are determined using two numbers that represent latitude and lon-
gitude. These numbers are actually two angles, measured in degrees (°), minutes of
arc ('), and seconds of arc (''). On a globe of the Earth, latitude lines circle parallel to
the equator, and differ in length depending on their location. The longest line is at the
equator (latitude 0 degrees); the shortest lines—actually pinpoints—are at the poles
(90 degrees north at the North Pole; 90 degrees [or 90 degrees] south at the South
Pole). In the Northern Hemisphere, latitude degrees increase as you move north away
from the equator; in the Southern Hemisphere, latitude degrees increase as you move
south away from the equator.
Longitude lines, or meridians (once called “meridian lines” and eventually short-
ened to “meridians”), are those that extend from pole to pole, slicing the Earth like seg-
ments of an orange, with each meridian crossing the equator. In the Western Hemi-
sphere, longitude increases as you move west from Greenwich, England (0 to 180
degrees). In the Eastern Hemisphere, longitude also increases as you move east from
Greenwich, England (again, 0 to 180 degrees). All points on the same line of longitude
experience true noon (and any other hour) at the same time. But note: Longitude lines
are not to be confused with time zones, most of which follow a more erratic demarca-
tion. (For more information on time zones, see below; for more information about lati-
tude and longitude with regard to polar coordinates, see “Geometry and Trigonometry.”)
Why is Greenwich, England,called the Prime Meridian?
The reason for Greenwich, England, being the Prime Meridian is historical. An imagi-
nary line passes through the old Royal Astronomical Observatory, which was chosen 415