Sky-checking for incoming comets, asteroids etc.

How is humanity currently monitoring the skies for potential bolide impacts? Is there any kind of official system or is it more or less left to chance observation?

There are many official programs all over the world. In the US, NASA does the bulk of the official tracking. They receive funding from Congress specifically for this task.

It’s not an easy task, though. NASA is currently tracking tens of thousands of objects, but it’s possible for them to miss an object. The meteor that came down in Russia a few years ago (and has videos all over youtube) wasn’t detected before it hit.

And, as any Sci-Fi fan will gladly tell you, in honour of Arthur C Clarke’s novel Rendezvous with Rama, where the name was coined, such programmes may get called Spaceguard, and are often lumped under that name generically.

If you haven’t seen this already, it’s pretty interesting (IMHO). Note the huge uptick in objects detected in the late 90s, which corresponds to when a lot of the detection programs received their first major funding. Improved technology helped with the uptick as well.

Asteroid Discovery from 1980 - 2011

There have also been very large objects (large enough to cause extinctions, IIRC) that have passed very close (closer than the Moon), and yet only been detected after their closest approach.

There is a system called Spaceguard which is much better than 10 years ago, but it is still limited:

About 14,723 Near Earth Objects (NEOs) have been discovered, and 1,717 are classified as Potentially Hazardous Objects.

As of 2011 over 93% of NEOs larger than 1 km have been found. However even a much smaller object is potentially very damaging. The 2013 meteor in Chelyabinsk Russia was probably only 20 meters in diameter. It was not detected and probably could not have been using current earth-based technology:

The Chelyabinsk meteor was probably the largest NEO to enter earth’s atmosphere since the 1908 Tunguska event:

However in 1972 a fairly large meteor formed a fireball above the Grand Tetons in the US, and it was filmed. The size is uncertain and has been estimated from 3 to 14 meters in diameter:

Still image:
Film: The Great Daylight 1972 Fireball - YouTube