Sick of the same old Druid rituals on the summer soltice?

Find the Earth’s Circumference Using Shadows
If you are sick of the same old tired Druid rituals on the summer solstice and have a healthy dose of skepticism about mundane things like the earths circumference you can duplicate an experiment Eratosthenes, a Greek geographer (about 276 to
194 b.c.) used to determine the earth’s circumference over two thousand years ago.

Eratosthenes:Father of geography or a guy with a lot of time on his hands?

Note: Although this experiment works best on the summer solstice when the sun is in its highest position in the sky for the year but can be tried throughout most of the year.
Estimated Time 20 Minutes

The ultimate measuring stick in NY's central Park

GEAR LIST
• Meter or yard stick, or a rod 3 to 5 feet long
• Carpenter’s t-square to help mea sure a vertical position for your
meter stick
• Tape
• String (at least twice as long as the stick)
• Protractor
• Large piece of paper or cardboard if you cannot adequately mark
the ground
• Globe or world atlas
• A sunny day

Author on the pyramid of the sun in Mexico

How to just do it!
1. Attach the string to the top of a stick approximately 3 to 5 feet
long.
2. Push the stick into a level area of ground or use a stand to achieve
a true vertical position.
3. Use the carpenters t-square to help achieve this vertical position.
4. Find solar noon in your area by consulting your local newspaper or
through going to http://solarnoon.com/ on the Internet.
5. At solar noon, pull the string taut to the end of the shadow of the
stick, and then carefully secure the string to that point on the
ground without tilting the stick.
Mea sure the length of your shadow. I put a ruler right on the
ground and mea sured the shadow directly.
FYI You can calculate solar noon for your location and time zone by
Knowing the exact midpoint between sunrise and sunset times.
Determine the angle between your string and stick by using a protractor.
If math is your thing, you can use the trigonometry formula of
cos x –1 of the length of shadow divided by height of stick.
In my case, in Central Park the angle was 40.5 degrees.
TIP: If you don’t know your latitude and longitude, check http:// ter
raserver -usa .com/
Determine the distance of your location from the equator by consulting
a globe, an atlas, the Web, or use the math formula that I used
for New York’s Central Park.
By my calculations, New York’s Central Park is 2794.3227 miles
from the equator.

Here is the math formula that I used. My mind gets foggy when I
hear the words math formula, but see if you can plug in your locations
to this step- by- step formula.
We know that Central Park’s Latitude is 40 degrees 74 minutes
north
Each degree = 60 minutes of arc
1 minute of arc = 1 nautical mile
40.74 (latitude of Central Park) × 60 (minutes of arc) = 2428.2 nautical
miles from the equator to Central Park.
1 nautical mile = 1.15077945 statue miles
2428.2 nautical miles × 1.15077945 = 2794.3227 statue miles.
• Apply your information to the formula below and you will know
the earth’s circumference!
024-39972_ch01_2P.indd 142 2/5/09 5:48:01 PM
Multiply your distance to the equator by 360 degrees, and then divide
by the mea sured angle at solar noon during the equinox. Your answer
should be that the circumference around the poles is 24,860 miles.
In my case I multiplied 2794.3 (my distance to the equator) by 360,
which yielded 1,005,948.
I divided by my solar noon angle of 40.5 degrees (1,005,948 ÷ 40.5)
which yielded my result of 24,838 miles. Not bad, but obviously not as
good as the Greek geographer Eratosthenes who did this many many
years before me—without a calculator.
For full dtails check out chapter 16 in Born to Explore

FYI The true circumference of the earth at the equator is actually
24,902.4 miles (40,076.5 km), due to the earth’s rotational speed
and Earth’s liquid outer core and solid inner. Did you know that
Earth is the densest known planet in the solar system?