Just to remind everyone that during its closest approach to the Earth comet ISON is supposed to be as bright, if not brighter than the FULL MOON

NASA's words originally, not mine!

Now just to put this into context, if you go outside you may be lucky to see Venus which is very bright but not as bright as ISON was/is predicted to be.

Now ISON's core or nucleus is supposedly just 3 miles in diameter, okay!

When it's supposed to be at it brightest ISON will be 39 Million Miles from the Earth, so that's a rock, 3 miles across will appear BRIGHTER than VENUS, which is around the same size as the Earth!

At the time of closest approach both ISON and VENUS will be around the same distance from the Earth, therefore in order for ISON to be brighter than VENUS one would logically assume it would need to be the same size or slightly bigger!

So, depending on how big it is forecast to be in our skies, and I don't know that for sure, it will need to be at least 12,000km in diameter, either the nucleus or the coma just to appear to be the same size as VENUS.