Because the word «ore» is dropped out from this common expression. This sentence above is short for «Il museo apre alle nove ore.». It is kind of like the difference between "The museum opens at nine," and "The museum opens at nine o'clock."
But why the "the"/"le" article? Wouldn't that be "at the nine"? or "at the nine o'clock"? Is that normally how time is expressed, with an article?
maybe think of it as 'at the ninth hour' even though it says nine and not ninth
For the 24-hour system, the expression is "at nine hundred hourS" or, for short, "at nine hours", "at fourteen", etc. So here, 'at the hours (time) of nine'. 'alle'.
To other complainers, i.e. not the OP with a fair enquiry, please embrace and accept Italian -and other language systems. They all have features that are as valid as or more logical than the one(s) you know. Let's learn Italian here.
What is wrong with what I wrote ? Is 9:00 really different from 9 ???
I believe strongly that this answer is correct!
Doulingo does not count the commas, question marks, dots, ...etc. in the answer. So, it understands 9:00 as 900 which is wrong in this case.
Because «nove» does not mean "night;" it means "nine," and «notte» means "night."
Also, in English, one would not say that a museum opens at the night; we would say that it opens at night, without the "the."
I replied with, "the museum opens at 9:00 am." This too was not accepted, but I thought it would make the exception given that I put "am" to indicate when. I guess the museum can also open at night as well. Plus, I realized too late that it doesnt recognize commas, quotations etc
I don't know. I ran that through a translator and got this, "il museo si apre il nono"...?
The museum opens at 9:00. I've used this notation in the past and it's been fine.