Grammar question. SOS. Calling all grammar fiends!!!

Question on comma splices and run on sentences.

I know this is a run of sentence: The chapel looms high above, it observes us with its apathetic stare. 

But what about: The chapel looms high above, observing us with its apathetic stare. 

I figure the word "observing" is a verb which connects to the first half of the sentence's subject but I am unsure. I have made a habit of this so I have become disensatized to it. I don't like using semi colons or periods too often because it feels choppy to me but I wonder if the second sentence is grammatically correct? Most of my University professors do not take marks off/mention the second format as being wrong but a few do so I am confused. Most online sources only use blatantly obvious comma splices as example as well so I have been unable to find a clear answer.