Peter Barker

**Ptolemy: Sizes and Distances **

**Question 1 **: The absolute distance to the moon, at closest approach, is 33 earth radii (e.r.). The absolute distance to the sun, at closest approach, is 1100 e.r.

Using a calculator (there is probably one in your cell phone):

(a) use the formula for the circumference of a circle to work out the circumferences, in earth radii, of the circles corresponding to the closest positions of the moon and sun.

(b) if the moon and sun both seem to be half a degree wide when viewed from the earth, how much larger, in earth radii, is the diameter of the sun than the diameter of the moon?

**Question 2 **: Using the materials provided, make a scale drawing of Ptolemy's cosmos, using the figures indicated
below. Label the spherical shell -- or orb -- corresponding to each object,
in the correct order. From your drawing, determine which planet has the thickest orb.

Planet |
Relative Distance |
Ptolemy |

Earth | greatest | |

least | ||

Jupiter | greatest | 14.4 |

least | 8.8 | |

Mars | greatest | 8.8 |

least | 1.2 | |

Mercury | greatest | 0.2 |

least | 0.06 | |

Saturn | greatest | 20.1 |

least | 14.4 | |

Sun | greatest | 1.2 |

least | 1.1 | |

Venus | greatest | 1.1 |

least | 0.2 |