"... no something" vs. "... not a something"

[Dmitry_86]

Dear friends!

I would like to know the difference between two well-known constructions "... no something" and "... not a something". Below I have provided several sentences to make it easier to understand what I am talking about:

1) All museums in Moscow and Saint-Petersburg are very beautiful and this one is no exception

All museums in Moscow and Saint-Petersburg are very beautiful and this one is not an exception

2) All courteous gentlemen are supposed to offer their seat to women, but Mike is no gentleman

All courteous gentlemen are supposed to offer their seat to women, but Mike is not a gentleman

3) In June there is twilight in our city instead of utter darkness and this is no surprise due to its geographical location

In June there is twilight in our city instead of utter darkness and this is not a surprise due to its geographical location

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Is there any difference between each two sentences in a particular pair?

Thanks!

 

[soccergal]

I see no difference in meaning in any of the pairs. I think no ... , sounds smoother and makes the point more strongly than not a...

 

[Dmitry_86]

Thanks a lot!

 

[Aardvark01]

The differences that strike me are degrees of formality and of impact.
The "not a" construct is more formal but the "no" construct has more impact, such as we would use to deliver the punchline of a joke.

"No exception" and "no surprise" can stand alone as comments in conversation but the longer forms:
"Not an exception" and "not a surprise" don't have the same impact/comic timing and I don't think I hear them used as stand alone comments in conversation.