Eratosthene's explanation of the sun's ray

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Discussion Overview

The discussion revolves around Eratosthenes' explanation regarding the sun's rays being overhead and their relation to the center of the Earth. Participants explore the implications of this phenomenon, particularly in the context of determining the Earth's radius and the geographical significance of Syene.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question how it can be said that the sun's rays pass through the center of the Earth when they are overhead, suggesting this may only apply to specific locations like Syene.
  • Others clarify that light from the Sun reaches all parts of the Earth that are in daytime, which is determined by the Earth's rotation.
  • A participant references Eratosthenes' measurements and the assertion that at Syene, a vertical stick casts no shadow, leading to the conclusion about the sun's rays passing through the Earth's center.
  • There is a discussion about the geographical positioning of Syene and how it was determined to be in the middle of the North and South.
  • Some participants note that the sun is directly overhead in various places on Earth, particularly in equatorial regions, and this can occur up to 23 degrees north or south of the equator.
  • One participant suggests that a diagram could help illustrate the concept of rays being perpendicular to the Earth's surface and extending through its center.

Areas of Agreement / Disagreement

Participants express uncertainty about the claim that the sun's rays pass through the center of the Earth, with some agreeing that this may only apply to specific locations. The discussion remains unresolved regarding the implications of Eratosthenes' conclusions and the geographical context of Syene.

Contextual Notes

There are limitations regarding the assumptions made about the sun's position and its implications for different geographical locations. The discussion also highlights the need for visual aids to clarify the geometric relationships involved.

prashant singh
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How can we say that when the sun is overhead then its ray will pass through the centre of the Earth , does it happens only at the one place on the earth. How they knew that synene is situated in the middle of north and south
 
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prashant singh said:
How can we say that when the sun is overhead then its ray will pass through the centre of the Earth , does it happens only at the one place on the earth. How they knew that synene is situated in the middle of north and south
What are you referring to?
What is 'synene ?
Light from the Sun reaches all parts of the Earth which are in daytime.
Daytime comes and goes because the Earth is rotating.
 
I am referring to the explanation given by eratosthenes ( BOOK :CONCEPTUAL PHYSICS BY PAUL G. HEWITS) in finding the radius of the earth. He said that there was a placed named syene near south of alexandria . Where we can see that a veritical stick or a line will not cast any shadow and he declared that at that place sun's ray would pass through the center of the earth. I want to know why or how he declared this statement
 
OK. I understand the question now.
Yes, the ancient greeks did make measurements of the Sun's shadow, and concluded that the Earth was probably a sphere.
 
But I want to know that how he concluded that when sun is overhead then its ray will pass through the centre, I think its only for that particular place (syene ) which must be situated in the middle of North and South ( if it so, then how they found that it is situated in the middle of North and South).
 
The sun is directly overhead in many places on Earth when that place on the Earth is directly facing the Sun.
It's common in equatorial regions and can happen as far as 23 degrees north or south of the equator, we call it 'Summer'.
At the poles it is never directly overhead, but it does get above the horizon.
 
Okkkkkk, but how can we say that its ray will pass through the center of the Earth when sun is overhead.
 
Doesn't it include a diagram? Can you draw yourself one? It should be obvious from a diagram.
 
prashant singh said:
Okkkkkk, but how can we say that its ray will pass through the center of the Earth when sun is overhead.
"Overhead" is taken to mean perpendicular to the surface of the Earth. Any line perpendicular to the surface of a sphere, and continuing thru the sphere, is a diameter. Try drawing it.
 
  • #10
Ohh thank u man it waa just a silly question , I forget that
 

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