Geoscience Reference
In-Depth Information
longitude from this stored waypoint later in the laboratory or you
can switch units in the field and gather a new waypoint in decimal
degrees (see step 2 above). Enter the value for decimal degrees in
Table 2.2 .
4. Repeat for the west end of your chosen track.
2.3.3 For further consideration: Polar circumference and
equatorial circumference
1. How does your calculated polar circumference compare with the
accepted polar circumference? You should be within 1% of the
accepted value of 40,008 kilometers (24,860 miles). What are some
reasons for why your answer may not be exactly the same as the
accepted circumference of the Earth? These include the fact that GPS
is not a perfect system, and while performing the activity multiple
times and averaging the values that you obtained will minimize error,
it will not eliminate error. GPS signals may bounce off buildings
before reaching your receiver (known as multipath error), heavy tree
cover may interfere with the GPS signals, or there may be fewer than
the optimal number of GPS satellites in view during the time of your
experiment.
2. How does the accepted polar circumference compare with Eratosthenes'
calculated circumference? Eratosthenes calculation of 46,250 kilome-
ters is 15.6% higher than the accepted modern value. The reasons why
Eratosthenes' circumference differs from the accepted polar circum-
ference include the reliance on the imperfect methods of counting
footfalls from people and camels from the surveyor team that trekked
across the desert to determine the distance between the two cities,
the fact that Alexandria is not due north of Syene, and the possibil-
ity that he may have thought that the Earth was perfectly spherical
and thus did not reduce the value of the equatorial circumference to
determine the polar circumference.
3. What do your polar and equatorial circumference calculations tell
you about the shape of Earth? Do some research and discuss why the
Earth has this shape. Your calculations alone should indicate that the
Earth is not a perfect sphere, but rather, that the Earth bulges around
its middle. Your research will show that the Earth is an oblate spher-
oid, and the larger equatorial circumference has to do with the rapid
rotation of the Earth and its molten core. The equatorial bulge is even
more pronounced with the gaseous planets Jupiter, Saturn, Uranus,
and Neptune, and with stars like our own Sun.
4. Using your calculated values, how long would it take to walk around the
Earth along the polar circumference (in days)? You can assume that you
can walk an average of 5 km/h, or if you want to check your actual aver-
age walking speed, use the speed function in your GPS while you are
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