Learn Hardcore Indonesian: Saya belajar di perpustakaan sampai perpustakaan tutup. - I study at the library until the library closes.

In Saya belajar di perpustakaan, the focus is on where you are studying: at the library. You are not describing movement; you are describing the place of the action.

If you want to talk about going there, you use ke:

Saya pergi ke perpustakaan. = I go to the library.
Saya berjalan ke perpustakaan. = I walk to the library.

So: di = static location; ke = movement toward a place.

Why is it tutup and not menutup or ditutup?

Base word:

tutup = closed / to close (stative / intransitive use)
menutup = to close (something) – active, needs an object
ditutup = is closed / was closed (by someone) – passive

In sampai perpustakaan tutup, tutup works like an adjective or an intransitive verb: until the library is closed / closes. There is no object.

Compare:

Perpustakaan tutup jam lima.
The library closes / is closed at five.
Petugas menutup perpustakaan jam lima.
The staff closes the library at five. (menutup
- object)
Perpustakaan ditutup jam lima.
The library is closed at five. (passive, someone closes it)

Your sentence just needs the state/event “the library closes”, so tutup is the natural form.

Can I say Saya belajar di perpustakaan sampai tutup without repeating perpustakaan?

Yes, that is natural and common:

Saya belajar di perpustakaan sampai tutup.
= I study at the library until it closes.

In context, tutup clearly refers to perpustakaan, so you can drop the second perpustakaan. Repeating it (as in the original sentence) is also correct; it just sounds a bit more explicit.

Both are acceptable:

…sampai perpustakaan tutup.
…sampai tutup.

Can I say sampai perpustakaan ditutup or sampai perpustakaan menutup? What’s the difference?

sampai perpustakaan ditutup
Grammatically OK, but it sounds like a passive event: until the library is closed (by someone). It’s a bit more formal and focuses on an action done by staff or an authority.
sampai perpustakaan menutup
This is not natural. menutup normally takes an object (to close something), so perpustakaan menutup sounds like “the library closes (something)” and feels incomplete.

Natural options:

…sampai perpustakaan tutup. (very normal)
…sampai perpustakaan ditutup. (possible, more like “…until the library is shut down/closed by staff”)
…sampai tutup. (short, very natural in speech)

What exactly is sampai doing here? Is it a conjunction like “until”? Can I use hingga instead?

In this sentence, sampai functions like the conjunction “until”:

Saya belajar di perpustakaan sampai perpustakaan tutup.
= I study at the library until the library closes.

sampai can work as:

Preposition (before a time or place):
- sampai jam lima = until five o’clock
- sampai rumah = until (I) reach home
Conjunction (before a clause):
- sampai perpustakaan tutup = until the library closes

You can usually replace sampai with hingga:

Saya belajar di perpustakaan hingga perpustakaan tutup.

hingga is a bit more formal or literary, but the meaning is basically the same here.

How do we know if this means “I studied”, “I am studying”, or “I will study”? There is no tense marker.

Indonesian verbs do not change form for tense. Saya belajar di perpustakaan sampai perpustakaan tutup is tense-neutral. The time is understood from context or from time words you add.

To specify time:

Past:
- Tadi saya belajar di perpustakaan sampai perpustakaan tutup.
  (Earlier today I studied…)
- Kemarin saya belajar di perpustakaan sampai perpustakaan tutup.
  (Yesterday I studied…)
Present (ongoing):
- Sekarang saya belajar di perpustakaan sampai perpustakaan tutup.
  (Right now I am studying…)
Future:
- Nanti saya akan belajar di perpustakaan sampai perpustakaan tutup.
- Besok saya belajar di perpustakaan sampai perpustakaan tutup.
  (Common in Indonesian: future sense from the time word, verb stays belajar.)

So the base sentence by itself can be translated according to context: study / am studying / will study.

What’s the difference between belajar and mempelajari?

Both relate to studying/learning, but usage is different:

belajar = to study / to learn (intransitive or with tentang)
- Saya belajar di perpustakaan. = I study at the library.
- Saya belajar tentang biologi. = I study about biology.
mempelajari = to study something (more formal, focused, transitive)
- Saya mempelajari biologi. = I study / examine biology (as a subject, often more serious or detailed study).

Your sentence uses belajar because it’s just “I study (there)”, not “I study [object X]” in a formal or detailed sense.

Saying Saya mempelajari di perpustakaan is wrong, because mempelajari must take a direct object:

Saya mempelajari hukum di perpustakaan.
I study law in the library.

Can I use aku instead of saya here? Does it change the meaning?

Grammatically, yes:

Aku belajar di perpustakaan sampai perpustakaan tutup.

The meaning (the action) is the same. The difference is in formality and style:

saya: neutral–polite, safe in almost all situations (formal, with strangers, at work).
aku: informal, intimate (friends, family, casual speech, songs).

So:

Writing an essay or talking to a teacher: prefer saya.
Chatting with close friends: aku is very natural.

Do I always have to put di perpustakaan right after belajar, or can I move it?

Standard, most natural order:

Saya belajar di perpustakaan sampai perpustakaan tutup.

Other orders can be grammatically possible but may sound less natural or marked, for example:

Saya di perpustakaan belajar sampai perpustakaan tutup.
Understandable, but unusual; sounds like you’re emphasizing di perpustakaan.

Indonesian word order is relatively flexible, but for neutral sentences it’s best to keep:

Subject – Verb – (Place) – (Time / other details)

So stick with belajar di perpustakaan in that order in normal speech and writing.

What’s the nuance difference between sampai perpustakaan tutup and something like sampai jam tutup perpustakaan or sampai jam lima?

All are acceptable; they just emphasize different things:

sampai perpustakaan tutup
Focuses on the event/state: until the library closes / is closed. It doesn’t say exactly what time; maybe everyone already knows.
sampai jam tutup perpustakaan
Literally: until the library’s closing time. Slightly more formal/explicit, still unspecific about the exact hour.
sampai jam lima
Until five o’clock. Here you give the exact time, without directly mentioning “closing”.

For example:

Saya belajar di perpustakaan sampai perpustakaan tutup.
I stay until whenever it closes.
Saya belajar di perpustakaan sampai jam tutup perpustakaan.
I stay until the official closing time.
Saya belajar di perpustakaan sampai jam lima.
I stay until 5 o’clock (whether or not that’s the exact closing time, context decides).