-Lew Thomas 4-28-01 |

First we shall apply Dawes Limit, which strictly applies to the resolution of two equally bright points of light. This is

R” = 4.56/D (1)

where

D = the diameter of the telescope objective in inches

R” = the resolving power in seconds of arc.

The mean distance of the Moon from Earth is 384,500 km. Therefore, the linear dimension of any object on its surface is

R = rq (2)

where

r = the distance to the Moon = 384,500 km.

q = the angle of the Moon object subtended at the Earth observer in radians

R = the linear dimension of the Moon object in km.

Combining (1) and (2), we have

R = r 4.56p/(3600×180 D)

R = 8.5003/D (3)

Using this relationship and assuming a perfect telescope, the following table is constructed

OBJECTIVE DIAMETER | MINIMUM DISCERNABLE CRATER |

INCHES | KILOMETERS |

Unaided eye (0.1 in.) | 85 |

4 | 2.12 |

6 | 1.42 |

8 | 1.01 |

10 | 0.85 |

20 | 0.43 |

100 | 0.09 |

200 | 0.04 |