NGC 2158 -- Open Cluster in Gemini
A Comet-like Open Cluster
Several decades ago, I stumbled on to NGC 2158 while observing the magnificent open
cluster M35 from a dark site.  I knew I had found a comet.  Once I was back in the office
with a star chart, my hopes for a new comet were squashed.  Instead, the location showed
NGC 2158 an open cluster that is 9,000 light-years more distant than M35.  The brightest
stars in this dense cluster (over 1,000 stars) only shines at magnitude 15 and were dimmer
than I could see with my telescope – and thus comet-like in my scope.

NGC 2158 is a tough find from the suburbs.  It does not do well with any light pollution.  
Obvious from a dark site with my 6-inch telescope, it is a challenge, using the same
telescope, from the deck of my suburban house.  Knowing exactly where to look is the key
from light-polluted skies and even then, you need a transparent sky, or it will not be visible.  
This rich, dim (magnitude 8.6), small open cluster (5 arcseconds) is worth looking for each
time you visit the bright (magnitude 5.1), huge (25 arcseconds) M35 cluster in Gemini.