18 Dec
2010
18 Dec
'10
8:23 p.m.
Coincidentally, Neptune's orbit is about where things in geocentric coordinates violate the Speed Limit. --rwg _______________________________________________ ES>You will also need a large telescope mirror to view the Earth image 2000 ly distant. At 10^13 km/ly, this is 2 x 10^19 m. In order to see 1 m details, it will need to resolve an angle of 5 x 10^-20 rad. The standard diffraction limit for wavelength λ and aperture diameter a is λ/a. For λ = 500 nm, the required mirror diameter is 10^13 m = 60 AU. This is the size of Neptune's orbit. The distant mirror also needs to be at least this big. -- Gene