How do you know which comets and asteroids can be viewed? The answers are found in the links below.
The outstanding website Heavens Above maintains a list of "Comets currently brighter than mag. 12" and "Minor planets currently brighter than mag. 10."
Bright Comets Currently Visible: Skyhound's monthly list of Comets Visible This Month.
So far, none of the objects listed here has hit the Earth. Keep your fingers crossed.....
-------------------------------------------------------------------------------------------------------------------------