Τη στιγμή που αλλάζει το σκηνικό, η πρόβα συνεχίζεται.

Because τη στιγμή is in the accusative, not the nominative.

In this sentence, τη στιγμή που... is a fixed time expression meaning something like at the moment when / while. Greek often uses the accusative in adverbial expressions of time.

So:

• η στιγμή = the moment as a subject
• τη στιγμή = at the moment / the moment when in this structure

Compare:

• Η στιγμή είναι σημαντική. = The moment is important.
• Τη στιγμή που μπήκε, όλοι σηκώθηκαν. = The moment he entered, everyone stood up.

Here που links the noun phrase τη στιγμή with the clause αλλάζει το σκηνικό.

So τη στιγμή που αλλάζει το σκηνικό means:

• the moment when the set changes
• or more naturally in English, when the set changes / while the set is changing

In this kind of sentence, που often works like when or that after a time expression.

Examples:

• την ώρα που μιλάω = while I’m speaking
• τη μέρα που έφυγε = the day he left

So it is not just the basic who/which/that you may have learned first; it is also very common after time expressions.

Αλλάζει is the present tense of αλλάζω (to change).

Greek often uses the present tense to describe:

• something happening now
• a scene being narrated as if it is happening now
• actions that happen simultaneously

Here, the sentence presents two actions as happening at the same time:

• αλλάζει το σκηνικό
• η πρόβα συνεχίζεται

So the present tense is very natural.

Also, this is the imperfective present, which focuses on the action as ongoing or in progress, not as a completed whole.

Το σκηνικό is a neuter noun. In a theater context, it usually means:

• the set
• the scenery
• stage setting

So:

• το σκηνικό αλλάζει = the set changes / the scenery changes

It is singular in Greek because it can refer to the set as one whole stage arrangement, even if English might sometimes think of it as collective.

Be careful not to confuse it with similar-looking words related to stage:

• η σκηνή = the stage or the scene
• το σκηνικό = the set / scenery / setting

Because it is the mediopassive form of συνεχίζω.

Greek often uses mediopassive forms where English uses an active intransitive verb. So:

• συνεχίζω κάτι = I continue something
• συνεχίζεται = it continues / it is continued

In this sentence, η πρόβα συνεχίζεται means the rehearsal continues.

Even though the form looks passive, the meaning in English is often just natural intransitive continues, not a strongly passive is being continued.

This is very common in Greek.

Usually, no—not with the same meaning.

The natural Greek way here is:

• η πρόβα συνεχίζεται

because συνεχίζω is normally transitive in the active voice:

• Συνεχίζω την πρόβα. = I continue the rehearsal.

When the rehearsal itself is the thing going on, Greek prefers the mediopassive:

• Η πρόβα συνεχίζεται. = The rehearsal continues.

So this is a good verb pair to learn as a pattern.

The comma separates the introductory time clause from the main clause.

Structure:

• Τη στιγμή που αλλάζει το σκηνικό, = subordinate time clause
• η πρόβα συνεχίζεται. = main clause

This is similar to English:

• When the set changes, the rehearsal continues.

Greek punctuation in this kind of sentence is very similar to English.

Yes. Greek word order is more flexible than English because the endings help show grammatical roles.

This sentence could also be rearranged, for example:

• Η πρόβα συνεχίζεται τη στιγμή που αλλάζει το σκηνικό.

That still means basically the same thing.

The version with the time expression first:

• Τη στιγμή που αλλάζει το σκηνικό, η πρόβα συνεχίζεται.

puts more focus on the timing or sets the scene first.

So the chosen order is natural and slightly more narrative.

They are often similar, but not always identical in tone.

• όταν = when
• τη στιγμή που = literally the moment when, and sometimes while

In many contexts, either can work:

• Όταν αλλάζει το σκηνικό, η πρόβα συνεχίζεται.
• Τη στιγμή που αλλάζει το σκηνικό, η πρόβα συνεχίζεται.

But τη στιγμή που can feel a bit more specific, scene-setting, or tied to that exact moment.

So όταν is often the more neutral option, while τη στιγμή που can sound a bit more vivid or precise.

Greek uses the definite article more often than English does.

In this sentence, both are specific things understood from the context:

• το σκηνικό = the set
• η πρόβα = the rehearsal

In English, you might sometimes omit an article in a more general style, but Greek usually keeps it when talking about a specific known thing in the situation.

Using the article here is completely normal and expected.

It breaks down like this:

• Τη στιγμή που = at the moment when / when
• αλλάζει = changes / is changing
• το σκηνικό = the set
• η πρόβα = the rehearsal
• συνεχίζεται = continues / is continued

So the grammar pattern is:

[time expression + subordinate clause], [main clause]

More abstractly:

Τη στιγμή που + verb..., main clause

This is a very useful pattern to learn, especially with other time nouns:

• την ώρα που... = while...
• τη μέρα που... = the day when...
• τη νύχτα που... = the night when...