![Comet Halley](https://www.astronomy.com/wp-content/uploads/sites/2/2023/02/asy-20010315-00710-orig-lg.jpg)
This photograph of Comet Halley was taken during its closest pass by Earth — 39 million miles.
NOAO
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.