What is a comet?

A comet is a small body in the solar system that orbits the Sun and may have a tail and atmosphere.  Its body is composed of rock, dust, and ice.

What does comet magnitude mean?

Magnitude is the measure of brightness as observed from Earth.  The lower the number, the brighter it is.  The Sun has a magnitude of -26, Jupiter is -2.8(17P/Holmes is currently brighter than Jupiter as of 11/07), and the faintest stars observable with out any magnification are +6.

How often does Comet 17P/Holmes come around?

It is a periodic Comet that will be visible from Earth every 6.9 years.

How big is Comet 17P/Holmes?

Before the most recent outburst, the nuclear diameter was estimated at 3.4 km.