Geoscience Reference
In-Depth Information
Table 2.2
Measuring the Earth's Equatorial Circumference
West point (latitude:
decimal degrees
)
a.
West point (longitude:
decimal degrees
)
b.
West point (UTM northing:
meters
)
c.
West point (UTM easting:
meters
)
d.
East point (latitude:
decimal degrees
)
e.
East point (longitude:
decimal degrees
)
f.
East point (UTM northing:
meters
)
g.
East point (UTM northing:
meters
)
h.
Distance in decimal degrees [b-f°]
i.
Distance in meters [h-d
meters
]
j.
Knowing the ratio
k.
Distance in decimal degrees [i]
360
Distance in meters [j]
[LC] me
=
°
ters
We can solve for the circumference of the Earth
along this line of latitude
[LC] in
kilometers
([j] meters * 360 )
[i]
°
1
1000
[LC] km
=
*
°
and to determine the equatorial circumference [EC] in
kilometers (use degrees not radians)
[EC] km
=
[LC]
cos (latitude [a])
To calculate % error (assuming a true equatorial circumference of 40,075 km)
l.
| [k] km 40,075 km |
40,075 km
−
[EC] % error
=
* 100
Note:
Remember your work on the activities in
Chapter 1
: Do not round off! Retain a minimum of five digits to the
right of the decimal point.
2. Locate a safe place away from buildings, cliffs, trees, power lines,
and other obstacles such that you will be able to walk in an east/west
direction for at least 200 meters—the longer the better (Note: You
may want to start at one of the points used for the polar circumfer-
ence calculation).
You can use the compass on a GPS set to true north or monitor the
GPS coordinates to make sure that you are following a true east-west
track. If you are following a true east-west track, the northings should
not change as you are walking.
3. Take a GPS reading at the east end of your chosen track (Note: If you
can “average” the points and then mark the waypoint, please do so
(and make sure that WAAS correction is enabled)). Name the way-
point with a meaningful name so that you can identify it later. Record
the UTM coordinates in Table 2.2. You can record the latitude and
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