How to Measure Earth?
Summary
TLDRIn 245 BC, Eratosthenes accurately calculated Earth's circumference using simple tools like a vertical stick and the angle of the noonday sun. Dave Cederberg from Purdue University's Saturday Morning Astrophysics Heritage teaches viewers how to replicate this experiment. By measuring a stick's shadow at solar noon and comparing it with another location's shadow, one can estimate Earth's size. The video offers various methods to ensure the stick's verticality and measure the shadow accurately, encouraging participation in the Eratosthenes project and sharing of results.
Takeaways
- 📅 In 245 BC, Eratosthenes calculated the Earth's circumference with remarkable accuracy.
- 📍 The experiment took place in Northern Egypt, specifically in Alexandria.
- 🎓 Eratosthenes was a polymath known for his contributions to mathematics, music, philosophy, and geography.
- 🌐 The method involved using a vertical stick, a measuring tool, and the position of the sun at solar noon.
- 📏 To replicate the experiment, one needs a vertical stick, a measuring tape or meter stick, and the sun's position at solar noon.
- ☀️ Solar noon is the time when the sun is at its highest point in the sky, which can be determined with a Google search.
- 🔍 The experiment requires aligning the pole vertically and measuring the shadow's length at solar noon.
- 📏 The shadow's length is measured from the pole's edge to the shadow's outer edge, with precision to the nearest 0.1 centimeter.
- 🔄 Various methods are shown to ensure the pole is vertical, including using a bubble level, a photographic tripod, a string and weight, or a cardboard structure.
- 📊 The experiment requires data from two locations to calculate the Earth's circumference, with additional data available for comparison.
- 🔗 The video description contains a link to resources for the complete lesson, teacher materials, and a study guide for the Eratosthenes project.
Q & A
Who was the mathematician, musician, philosopher, and geographer that calculated the circumference of the Earth in 245 BC?
-The mathematician, musician, philosopher, and geographer who calculated the circumference of the Earth in 245 BC was Eratosthenes.
What tools did Eratosthenes use to calculate the Earth's circumference?
-Eratosthenes used a vertical stick, a measuring tape or meter stick, and the Noonday Sun to calculate the Earth's circumference.
How did the shadow's length and the Noonday Sun help Eratosthenes in his calculations?
-The shadow's length and the Noonday Sun helped Eratosthenes by allowing him to compare the angles of the sun's rays in different locations, which he used to calculate the Earth's circumference.
What is solar noon and why is it important for this experiment?
-Solar noon is when the sun is at its highest point in the sky, which is important for the experiment because it provides the most accurate shadow length measurements for calculating the Earth's circumference.
How can one determine the exact time of solar noon at their location?
-One can determine the exact time of solar noon at their location with a simple Google search.
What is required to ensure the pole used in the experiment is vertical?
-To ensure the pole is vertical, one can use a bubble level, a photographic tripod with a string, a wooden dowel with a hook and string, or a cardboard structure with a vertical stick.
How should the length of the shadow be measured during the experiment?
-The length of the shadow should be measured from the edge of the pole to the outside edge of the shadow, to the nearest 0.1 centimeter.
Why is it necessary to have two locations to complete the calculations in this experiment?
-Having two locations is necessary to compare the shadow lengths and the angles of the sun's rays, which is crucial for calculating the Earth's circumference.
What resources are provided for those who want to participate in the Eratosthenes project experiment?
-Participants in the Eratosthenes project experiment are provided with a link to a complete written lesson, teacher resources, a data study guide, and photos of others doing the experiment.
How can one share their results and ask questions about the Eratosthenes project experiment?
-One can share their results and ask questions by contacting the organizers through the provided link in the video description.
Outlines
🌏 Eratosthenes' Experiment on Earth's Circumference
In 245 BC, Eratosthenes, a mathematician, musician, philosopher, and geographer from Northern Egypt, calculated the Earth's circumference with remarkable accuracy. He used a simple method involving a vertical stick, a measuring tool, and observations of the Noonday Sun. Dave Cederberg from Purdue University's Saturday Morning Astrophysics Heritage introduces a way to replicate Eratosthenes' experiment. To perform this, one needs a vertical stick, a measuring tape or meter stick, and the Noonday Sun. The experiment involves measuring the shadow cast by the stick at solar noon, the time when the sun is at its highest point in the sky. Solar noon can be determined with a Google search. The stick must be aligned vertically, and the shadow's length must be measured accurately. The video provides multiple methods to ensure the stick's vertical alignment and to measure the shadow. The experiment can be completed with the help of a link provided in the video description, which offers a complete lesson, teacher resources, and a data study guide.
Mindmap
Keywords
💡Eratosthenes
💡Circumference
💡Vertical Stick
💡Noonday Sun
💡Shadow
💡Measuring Tape
💡Solar Noon
💡Geography
💡Astronomy
💡Experiment
💡Educational Content
Highlights
In 245 BC, Eratosthenes calculated the Earth's circumference with surprising accuracy using a simple method.
The method involves using a vertical stick, a measuring tape, and the Noonday Sun to measure shadows.
Dave Cederberg from Purdue University explains how to replicate Eratosthenes' experiment.
The experiment requires a vertical stick, a measuring tape, and the measurement of a shadow at solar noon.
Solar noon is when the sun is at its highest point in the sky, which can be determined with a Google search.
The pole must be aligned vertically, which can be achieved with a bubble level or other methods shown.
The length of the shadow cast by the pole is measured at solar noon.
Multiple ways to ensure the pole is vertical are demonstrated, including using a tripod and a string.
The shadow's length is measured from the edge of the pole to the outside edge of the shadow.
The measurement should be taken to the nearest 0.1 centimeter for accuracy.
Two locations are needed to complete the calculations for the Earth's circumference.
The video provides a link to other locations for comparison and to complete the calculations.
A complete written lesson, teacher resources, and a data study guide are available for the experiment.
The video encourages viewers to share their results and questions, and to send photos of their experiments.
Transcripts
the year 245 BC the place Northern Egypt
a curious mathematician musician
philosopher and geographer calculated
the circumference of the earth to
surprising accuracy armed with a
vertical stick a meter stick or
measuring tape and the Noonday Sun you
can do it too
hi this is Dave cederberg from Purdue
Saturday morning astrophysics Heritage
the knees in the great city of
Alexandria Egypt learned that the shadow
cast by an object in the Noonday sun was
longer or shorter than the shadow cast
in a more Northern or Southern location
based on the comparative difference
between the angles of the sun's rays and
the distance between the two locations
eratosthenes found a way to calculate
the circumference of the Earth
I'm going to show you how to repeat
eratosthenese experiment and you can do
it for yourself
in order to do this experiment you will
need some sort of vertical stick or pull
you'll need a measuring tape or meter
stick a way to measure the length of the
Shadow and you'll need the Noonday Sun
you will need to know the length of the
pole and the length of the shadow that
it casts you'll want to take your
measurement at exactly solar noon now
solar noon is when the sun is at its
highest point in the sky you can figure
out solar noon at your location with a
simple Google search
at solar noon you want to align the pole
exactly vertically we'll show you
multiple ways to do this on this pole we
have a little bubble level on the top so
we can tell when it's perpendicular to
the ground you need a level surface on
the ground and at the right time solar
noon measure the length of the Shadow
[Music]
from the edge of the pole to the outside
edge of the Shadow and in this case we
have about 39.5 centimeters measure the
length to the nearest 0.1 centimeter
we'll show you another way to create a
vertical pull we have a photographic
tripod I have a wooden dowel with the
hole drilled through it and a string to
hang it from the handle of the tripod we
want to make sure that it just barely
touches the ground hangs vertical and
then we can measure the shadow
here's yet another way to create a
vertical pole we have a wooden dowel rod
a hook a string and a weight
when the string hangs parallel to the
rod we know that it's vertical we're
using gravity
and we can then measure the shadow
all right and here's still another way
we've taken some cardboard squares or
triangles glued them together to make a
corner and glued a vertical stick in the
corner if I set this down on level
ground it'll be vertical and I can
measure the shadow
just like your attached the knees you
will need two locations to complete your
calculations
you have your own data once you record
your data and upload it we'll provide
you a link to other locations that you
can use to compare and complete your
calculations there is a link in the
description of the video to give you
access to the complete written lesson
teacher resources data study guide and
photos of others doing the experiment we
hope you have fun with our eratosthenes
project experiment share your results
let us know if you have any questions
and send us photos if you can
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