Dziewiątego maja otwierają nową wystawę w muzeum.

In Polish, dates are usually expressed with:

• an ordinal number for the day
• the month in the genitive case

So:

• dziewiąty = ninth
• dziewiątego = of the ninth / on the ninth (the form used in dates)
• maj = May
• maja = of May

So dziewiątego maja means on the ninth of May.

This is the normal Polish way to say a date in running text.

Polish usually does not need a preposition like on before dates.

So English:

• on the ninth of May

becomes simply Polish:

• dziewiątego maja

That whole phrase works as a time expression by itself.

A very literal version with an extra word is possible in some contexts, for example w dniu dziewiątego maja, but that sounds more formal and is not the normal everyday way.

Both words are in the genitive:

• dziewiątego = genitive of dziewiąty
• maja = genitive of maj

This is standard for Polish dates.

You can think of it as an abbreviated version of something like dziewiątego dnia maja (of the ninth day of May), though native speakers just say dziewiątego maja.

Polish often uses the present tense of an imperfective verb for a planned or scheduled future event.

So otwierają literally looks like they open / they are opening, but in this sentence it means:

• they are opening
• they will open
• the opening takes place

because the date already makes it clear the event is in the future.

This is very natural in Polish, especially for schedules, programs, announcements, and planned events.

The sentence does not name the subject directly.

Otwierają is 3rd person plural, literally they open / they are opening. In Polish, this form is often used when:

• the doer is unknown
• the doer is obvious from context
• the exact subject is not important

So here it can mean something like:

• they’re opening a new exhibition at the museum
• the museum is opening a new exhibition
• people are opening a new exhibition there

It is a common way to make the sentence sound natural without specifying exactly who they are.

Because wystawę is the direct object of otwierają.

The verb otwierać takes an object in the accusative case. Since wystawa is a feminine noun, its accusative singular is:

• wystawa → nominative
• wystawę → accusative

The adjective has to match the noun, so:

• nowa wystawa = a new exhibition
• nową wystawę = a new exhibition (as the object)

So in this sentence:

• otwierają nową wystawę = they are opening a new exhibition

Because w muzeum means in the museum, referring to location.

• w muzeum = in the museum
• do muzeum = to the museum

Here the exhibition is being opened at that location, so Polish uses w plus the locative case:

• muzeum → locative singular: muzeum

This noun happens to look the same in nominative and locative, but the case is still locative after w when it means in.

Otwierają comes from otwierać, which is imperfective.

That matters because:

• the present tense of an imperfective verb can refer to a scheduled future
• the present tense of a perfective verb usually refers to a future result and is formed differently

Here, otwierają fits well because the sentence is presenting the opening as an event on the schedule.

A related perfective verb would be otworzyć. A sentence with that verb would be built differently, for example:

• Dziewiątego maja otworzą nową wystawę w muzeum.

That also means On May 9 they will open a new exhibition at the museum, but it sounds a bit more like a completed future action.

Yes. Polish word order is fairly flexible, because case endings show the grammatical roles.

The original sentence:

• Dziewiątego maja otwierają nową wystawę w muzeum.

is a very natural neutral order.

But you could also say:

• W muzeum otwierają dziewiątego maja nową wystawę.
• Nową wystawę otwierają dziewiątego maja w muzeum.

These versions are grammatical, but the focus changes slightly. Polish word order often helps show what is being emphasized.

So the original sentence is probably the best neutral version for a learner.

Yes. In writing, Polish often uses the numeral:

• 9 maja

This is very common and completely natural.

When read aloud, it is usually read as:

• dziewiątego maja

So:

• 9 maja otwierają nową wystawę w muzeum.
• Dziewiątego maja otwierają nową wystawę w muzeum.

mean the same thing.

If you want to name who is doing it, you can add a subject. For example:

• Muzeum otwiera dziewiątego maja nową wystawę. = The museum is opening a new exhibition on May 9.
• Pracownicy muzeum otwierają dziewiątego maja nową wystawę. = The museum staff are opening a new exhibition on May 9.

Once you add a subject, the sentence becomes more specific. Without it, the original version sounds broader and more announcement-like.

It is pronounced roughly like דזשев-yon-te-go in English-style approximation, though not exactly.

It seems long because it contains:

• the stem of dziewiąty (ninth)
• an ending showing the correct case: -ego

Polish ordinal numbers often become quite long when they change for case.

For example:

• dziewiąty = ninth
• dziewiątego = of/on the ninth
• dziewiątemu = to the ninth

So the length is normal—it is just the number changing form to fit the grammar.