How to Measure Earth?

Summary

In 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.