From the October 2009 issue

How to determine atmospheric extinction

Use this table to refine your comet observing.
By | Published: October 26, 2009
Comet Halley
This photograph of Comet Halley was taken during its closest pass by Earth — 39 million miles.

In the December 2009 issue, I wrote the story, “How to observe comets.” In it, I suggest all observers estimate how bright a comet appears. To get the whole picture, however, you must factor in one other thing.