Chúng ta ngắm trời.

Chúng ta means we including the listener. It is the inclusive we.

By contrast, chúng tôi means we but not including the listener.

So in Chúng ta ngắm trời, the speaker is including the person they are talking to.

Yes, mostly. This sentence follows a simple Subject + Verb + Object pattern:

• Chúng ta = subject
• ngắm = verb
• trời = object

So the structure is very straightforward for an English speaker.

Because in Vietnamese, ngắm can take its object directly.

So:

• ngắm trời = literally gaze the sky
• natural English = gaze at the sky

English needs at here, but Vietnamese does not.

Vietnamese does not use articles like a, an, and the the way English does.

A noun like trời can often stand on its own, and the listener understands from context whether it means something general or specific. In this sentence, it is naturally understood as the sky.

Not exactly.

Ngắm usually means to look at something attentively, appreciatively, or for a while. It often has a sense of admiring or contemplating.

Compare:

• nhìn = look, see
• ngắm = gaze at, admire, contemplate
• xem = watch, look at, check

So ngắm trời sounds more like gazing at the sky than just looking at the sky.

Here, trời means sky.

But trời is a very flexible word in Vietnamese. In other contexts, it can also refer to:

• weather: Hôm nay trời đẹp = The weather is nice today.
• heaven / the heavens
• an exclamation, like Oh my God! in expressions such as Trời ơi!

So context is very important.

Yes. Bầu trời also means sky, and it is a bit more explicit.

So both are possible:

• ngắm trời
• ngắm bầu trời

Trời is shorter and very common. Bầu trời can sound a little fuller or more descriptive.

Yes, it is understandable and natural, but it can sound a little poetic or reflective because of ngắm.

If you just mean we look up at the sky, you might also hear:

• Chúng ta nhìn trời
• Chúng ta nhìn lên trời

Using ngắm suggests more of a calm, appreciative gaze.

Yes, a few:

• chúng has a rising sắc tone
• ta has a level tone
• ngắm also has a rising sắc tone
• trời has a falling huyền tone

Also:

• ng can start a word in Vietnamese, unlike in English. It is the same sound as the end of English sing, but moved to the beginning.
• tr and ch are different consonants in careful Vietnamese pronunciation.

So tones and initial consonants both matter here.