Gece seferinin sefer numarası değişti.

A useful way to parse it is:

• gece seferi = night service / night trip
• gece seferinin = of the night service
• sefer numarası = service number / trip number / flight number depending on context
• değişti = changed

So the whole sentence is:

• Gece seferinin sefer numarası değişti.
• Literally: The night service's service number changed.
• More natural English: The flight/service number of the night service changed.

The verb comes at the end, which is the normal Turkish pattern.

Because it belongs to two different chunks:

• gece seferi = night service
• sefer numarası = service number / flight number

So the sentence is built from two expressions that both happen to contain sefer.

This is not strange in Turkish, even if English would often avoid repeating the same word. Turkish is being very explicit here.

No. That is a very common beginner question.

Here, seferi is not a direct object. The -i is part of a noun compound structure. In Turkish, when one noun modifies another noun, the second noun often takes the ending -(s)I.

So:

• gece seferi = night service
• not the night service as an object

Other examples of the same pattern:

• otobüs bileti = bus ticket
• yaz tatili = summer holiday
• oda numarası = room number

So in this sentence, seferi is just the normal form inside the compound gece seferi.

It is the genitive ending, which often corresponds to English of or 's.

So:

• gece seferi = night service
• gece seferinin = of the night service / the night service's

This marks gece seferi as the possessor of sefer numarası.

A simple way to see it:

• X-in Y-si = Y of X / X's Y

Here:

• gece seferinin sefer numarası = the night service's service number

Because Turkish normally uses numara in a compound or possessive structure here.

• sefer numarası = service number
• oda numarası = room number
• telefon numarası = phone number

The ending -sı is the usual -(s)I ending. The s is a buffer consonant because numara ends in a vowel.

So:

• numara = number
• numarası = its number / number of ... / number in a compound

In this sentence, numarası is the natural grammatical form.

Because gece seferi is a normal compound-like expression meaning night service.

Turkish very often uses a bare noun to modify another noun:

• gece seferi = night service
• yaz okulu = summer school
• köy evi = village house

If you said gecenin seferi, that would be a different structure, more like the service of the night. Grammatically possible in some contexts, but it is not the usual way to say night service.

So gece seferi is the idiomatic form here.

Değişti is the simple past of değişmek, meaning to change.

So:

• değişti = changed

In this sentence, the subject is gece seferinin sefer numarası, so the meaning is:

• The night service's number changed.

This is a 3rd person singular verb form. Turkish does not need an extra word for it here.

These forms mean different things:

• değişti = changed
• değiştirdi = changed it / caused it to change
• değiştirildi = was changed

So:

• Sefer numarası değişti. = The service number changed.
• Birisi sefer numarasını değiştirdi. = Someone changed the service number.
• Sefer numarası değiştirildi. = The service number was changed.

Turkish often uses değişti where English might sometimes prefer was changed, depending on context. But grammatically, değişti is the intransitive form: the number itself changed.

Turkish does not have articles like English a and the.

Instead, definiteness usually comes from:

• context
• word order
• possessive/genitive constructions

Here, the structure gece seferinin sefer numarası is naturally interpreted as a definite phrase, so in English you normally translate it with the:

• the night service's number
• the number of the night service

So there is no separate word for the; the grammar of the phrase already makes it specific.

Yes, in many contexts that would be understandable and may even sound more natural if the context already makes clear that you mean the service number.

Compare:

• Gece seferinin sefer numarası değişti. = very explicit
• Gece seferinin numarası değişti. = The night service's number changed

The original sentence keeps sefer numarası, which is a standard expression like flight number or service number. So it sounds more precise.

A little, yes, but the given order is the neutral one.

Turkish usually puts the verb at the end:

• Gece seferinin sefer numarası değişti.

You can move things around for emphasis, but not every rearrangement sounds equally natural. The original sentence is a normal, straightforward way to say it.

As a learner, the safest pattern is:

• [subject phrase] + [verb]

So here:

• Gece seferinin sefer numarası
  • değişti