problem with the word "number" plurial or singular (there are a large number of...)

I would have said : "there is a large number of galaxies"... Why must we say "there are" ?
And, what is the right sentence : "the large number of galaxies is" or "the large number of galaxy are" ?

Thank you !

[MrPedantic]

Hello Unreg,

1. The number of visitors to the website has decreased.
2. A number of visitors to the website have complained about its controversial content.

It depends on the meaning of the sentence.

In #1, for example, it is the number that has "decreased". The underlined part simply qualifies "number". So the verb is singular.

In #2, on the other hand, it is the visitors who have "complained". The underlined part simply qualifies (pre-modifies) "visitors". So the verb is plural.

Let me know if it's still puzzling!

Best wishes,

MrP