Describe the Ptolemaic model of the solar system. How did Ptolemy ...

[tichca]

Describe the Ptolemaic model of the solar system. How did Ptolemy account for the apparent retrograde motion of the planets?
 
  What will be an ideal response?

Question 2

Using an orbit size of 8 kpc, and a period of 225 million years, the mass of our Galaxy is found to be closest to
 
  A) 106 solar masses.
  B) 108 solar masses.
  C) 1010 solar masses.
  D) 1011 solar masses.
  E) 1012 solar masses.

[Ptupou85]

Answer to Question 1

Although Ptolemy's model was an Earth-centered model of the solar system, it was sufficiently accurate to remain in use for 1,500 years. His model used the ancient idea that all motions in the heavens must be perfect circles. Therefore, the planets moved on circles that orbited on larger circles around Earth. This circle upon circle motion accounted for the apparent retrograde motion of the planets. Ptolemy carefully selected sizes for the circles to reproduce the motions seen in the sky. He also placed Earth slightly off-center to improve model predictions even more.

Answer to Question 2

D

[tichca]

Both answers were spot on, thank you once again

[Ptupou85]

Great! Please up vote