Мы не могли не аплодировать, когда в конце оперы занавес медленно закрылся.

Yes — this is a common Russian pattern where a double negative creates the meaning could not help doing something or had to do something.

So:

• не могли не аплодировать = literally could not not applaud = naturally couldn’t help applauding

It does not mean simple negation like we could not applaud. That would be:

• Мы не могли аплодировать = We were unable to applaud

The second не is essential here.

Because after мочь (can / be able to), Russian normally uses an infinitive.

So:

• могли аплодировать = could applaud
• не могли не аплодировать = could not help applauding

This is similar to English could applaud, not could applauded.

The finite verb is могли, and аплодировать stays in the infinitive.

Могли is the past plural form of мочь because the subject is мы (we).

Past tense in Russian agrees with the subject in number and, in the singular, also in gender:

• я мог / я могла
• ты мог / ты могла
• он мог
• она могла
• мы могли
• они могли

There is no form моглись here, because мочь is not used reflexively in this sentence.

Because когда introduces a subordinate clause.

Main clause:

• Мы не могли не аплодировать

Subordinate time clause:

• когда в конце оперы занавес медленно закрылся

Russian normally puts a comma before subordinate clauses introduced by words like когда, если, потому что, что, and so on.

So the comma here is standard Russian punctuation.

Because the expression в конце means at the end of, and after конец / конце in this meaning, Russian uses the genitive.

So:

• в конце оперы = at the end of the opera
• в конце фильма = at the end of the film
• в конце книги = at the end of the book

The noun опера becomes оперы in the genitive singular.

This is a fixed and very common pattern.

Because занавес is the subject of закрылся.

In the clause:

• занавес медленно закрылся

the curtain is the thing performing or undergoing the action, so it appears in the nominative case:

• занавес = the curtain

If it were a direct object, you would expect a different structure, but here it is the subject of the verb.

Historically, -ся is related to reflexive meaning, and sometimes it can feel like itself, but in many verbs it is just part of the normal verb form and should not be translated literally.

Here:

• закрылся means closed / came down

With занавес, this is very natural Russian. You can think of it as the curtain closed rather than someone explicitly closed the curtain.

Compare:

• Он закрыл дверь = He closed the door
• Дверь закрылась = The door closed
• Занавес закрылся = The curtain closed / came down

So -ся often makes the verb intransitive or changes the focus from the doer to the event itself.

Because закрылся is perfective, and perfective aspect is used for a completed event.

Here the sentence refers to a single finished moment at the end of the opera:

• the curtain closed
• that event happened
• then the audience applauded

So закрылся fits well.

If you used закрывался, that would be imperfective, suggesting process, repetition, or background action:

• занавес закрывался = the curtain was closing

That is possible in some contexts, but in this sentence Russian prefers закрылся because the action is presented as a completed whole.

Yes. Literally it means the curtain slowly closed, but in the context of a theater or opera, English often says the curtain came down.

So this is a good example where a natural English translation may be less literal than the Russian wording.

Russian is describing the physical action of the curtain closing; English often uses the idiomatic theater phrase came down.

Russian word order is more flexible than English word order, so yes, it could be changed.

In the sentence:

• занавес медленно закрылся

медленно modifies закрылся and is placed in a neutral, natural position before the verb.

Other orders are possible, for example:

• занавес закрылся медленно
• медленно закрылся занавес

But they may sound more marked, poetic, or emphasize different parts of the sentence.

The given order is simply the most neutral and straightforward.

Because the object can be omitted when it is obvious or unimportant.

In context, аплодировать often implies applauding the performers, the production, or the performance in general. Russian does not need to say exactly whom they applauded if the situation already makes it clear.

If you wanted to state the object, аплодировать normally takes the dative:

• аплодировать певцам = to applaud the singers
• аплодировать артистам = to applaud the performers

But in this sentence, the general idea we applauded is enough, so no object is needed.