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Where did Ptolemy compare the Earth to the distance of fixed stars?

1

$begingroup$

I read the following in C. S. Lewis, Miracles (page 77-8)

The immensity of the universe is not a recent discovery. More than seventeen hundred years ago Ptolemy taught that in relation to the distance of the fixed stars the whole Earth must be regarded as a point with no magnitude.

There was no reference given, but I assume this would be in the Almagest. However, I don't know where in that work (or elsewhere) Ptolemy discussed this. I want to read his explanation for that view.

Hence the question: Where did Ptolemy compare the Earth to the distance of fixed stars?

astronomy

share|improve this question

asked 5 hours ago

Frank HubenyFrank Hubeny

10816

New contributor

Frank Hubeny is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

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add a comment | 

1

$begingroup$

I read the following in C. S. Lewis, Miracles (page 77-8)

The immensity of the universe is not a recent discovery. More than seventeen hundred years ago Ptolemy taught that in relation to the distance of the fixed stars the whole Earth must be regarded as a point with no magnitude.

There was no reference given, but I assume this would be in the Almagest. However, I don't know where in that work (or elsewhere) Ptolemy discussed this. I want to read his explanation for that view.

Hence the question: Where did Ptolemy compare the Earth to the distance of fixed stars?

astronomy

share|improve this question

asked 5 hours ago

Frank HubenyFrank Hubeny

10816

New contributor

Frank Hubeny is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

add a comment | 

$begingroup$

I read the following in C. S. Lewis, Miracles (page 77-8)

The immensity of the universe is not a recent discovery. More than seventeen hundred years ago Ptolemy taught that in relation to the distance of the fixed stars the whole Earth must be regarded as a point with no magnitude.

There was no reference given, but I assume this would be in the Almagest. However, I don't know where in that work (or elsewhere) Ptolemy discussed this. I want to read his explanation for that view.

Hence the question: Where did Ptolemy compare the Earth to the distance of fixed stars?

astronomy

share|improve this question

asked 5 hours ago

Frank HubenyFrank Hubeny

10816

New contributor

Frank Hubeny is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this question

asked 5 hours ago

Frank HubenyFrank Hubeny

10816

New contributor

Frank Hubeny is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

asked 5 hours ago

Frank HubenyFrank Hubeny

10816

New contributor

Frank Hubeny is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 5 hours ago

Frank HubenyFrank Hubeny

10816

New contributor

Frank Hubeny is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 5 hours ago

Frank HubenyFrank Hubeny

10816

2 Answers
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1

$begingroup$

Almagest, Book 1, chap. 5 ................

share|improve this answer

answered 4 hours ago

sand1sand1

90957

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  This basically answered my question where in the Almagest I need to look.
  $endgroup$
  – Frank Hubeny
  34 mins ago
  

  
  
  
  

add a comment | 

2

$begingroup$

Ptolemy's argument can be simply explained in plain English. If the distance to stars
was comparable to the size of the Earth, the stars would experience a diurnal parallax, that is the visible relative positions of the stars in the sky would change during one night. But this is not observed.

By the way, a similar argument will imply that if the Earth is rotating about the Sun
(or moves in some other way), the distance to the stars must be much larger than the size of this motion. In particular the diameter of the orbit of the Earth around the Sun is negligible in comparison to the distance to the stars.

This was the most serious argument against the Heliocentric system, and it is also
due to Ptolemy. Until the acceptance of Copernicus theory, people just could not believe that the distance to the stars can be so large.

share|improve this answer

answered 1 hour ago

Alexandre EremenkoAlexandre Eremenko

25.7k13694

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Thank you for confirming that it was parallax and for connecting this to questions about the Heliocentric system.
  $endgroup$
  – Frank Hubeny
  35 mins ago
  

  
  
  
  

add a comment | 

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1

$begingroup$

Almagest, Book 1, chap. 5 ................

share|improve this answer

answered 4 hours ago

sand1sand1

90957

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  This basically answered my question where in the Almagest I need to look.
  $endgroup$
  – Frank Hubeny
  34 mins ago
  

  
  
  
  

add a comment | 

1

$begingroup$

Almagest, Book 1, chap. 5 ................

share|improve this answer

answered 4 hours ago

sand1sand1

90957

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  This basically answered my question where in the Almagest I need to look.
  $endgroup$
  – Frank Hubeny
  34 mins ago
  

  
  
  
  

add a comment | 

$begingroup$

Almagest, Book 1, chap. 5 ................

share|improve this answer

answered 4 hours ago

sand1sand1

90957

$endgroup$

share|improve this answer

answered 4 hours ago

sand1sand1

90957

answered 4 hours ago

sand1sand1

90957

answered 4 hours ago

sand1sand1

90957

2

$begingroup$

Ptolemy's argument can be simply explained in plain English. If the distance to stars
was comparable to the size of the Earth, the stars would experience a diurnal parallax, that is the visible relative positions of the stars in the sky would change during one night. But this is not observed.

By the way, a similar argument will imply that if the Earth is rotating about the Sun
(or moves in some other way), the distance to the stars must be much larger than the size of this motion. In particular the diameter of the orbit of the Earth around the Sun is negligible in comparison to the distance to the stars.

This was the most serious argument against the Heliocentric system, and it is also
due to Ptolemy. Until the acceptance of Copernicus theory, people just could not believe that the distance to the stars can be so large.

share|improve this answer

answered 1 hour ago

Alexandre EremenkoAlexandre Eremenko

25.7k13694

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Thank you for confirming that it was parallax and for connecting this to questions about the Heliocentric system.
  $endgroup$
  – Frank Hubeny
  35 mins ago
  

  
  
  
  

add a comment | 

2

$begingroup$

Ptolemy's argument can be simply explained in plain English. If the distance to stars
was comparable to the size of the Earth, the stars would experience a diurnal parallax, that is the visible relative positions of the stars in the sky would change during one night. But this is not observed.

By the way, a similar argument will imply that if the Earth is rotating about the Sun
(or moves in some other way), the distance to the stars must be much larger than the size of this motion. In particular the diameter of the orbit of the Earth around the Sun is negligible in comparison to the distance to the stars.

This was the most serious argument against the Heliocentric system, and it is also
due to Ptolemy. Until the acceptance of Copernicus theory, people just could not believe that the distance to the stars can be so large.

share|improve this answer

answered 1 hour ago

Alexandre EremenkoAlexandre Eremenko

25.7k13694

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Thank you for confirming that it was parallax and for connecting this to questions about the Heliocentric system.
  $endgroup$
  – Frank Hubeny
  35 mins ago
  

  
  
  
  

add a comment | 

$begingroup$

Ptolemy's argument can be simply explained in plain English. If the distance to stars
was comparable to the size of the Earth, the stars would experience a diurnal parallax, that is the visible relative positions of the stars in the sky would change during one night. But this is not observed.

By the way, a similar argument will imply that if the Earth is rotating about the Sun
(or moves in some other way), the distance to the stars must be much larger than the size of this motion. In particular the diameter of the orbit of the Earth around the Sun is negligible in comparison to the distance to the stars.

This was the most serious argument against the Heliocentric system, and it is also
due to Ptolemy. Until the acceptance of Copernicus theory, people just could not believe that the distance to the stars can be so large.

share|improve this answer

answered 1 hour ago

Alexandre EremenkoAlexandre Eremenko

25.7k13694

$endgroup$

share|improve this answer

answered 1 hour ago

Alexandre EremenkoAlexandre Eremenko

25.7k13694

answered 1 hour ago

Alexandre EremenkoAlexandre Eremenko

25.7k13694

answered 1 hour ago

Alexandre EremenkoAlexandre Eremenko

25.7k13694