Đêm rất yên tĩnh.

Vietnamese often does not use a verb equivalent to to be when describing something with an adjective.

So:

• Đêm rất yên tĩnh = The night is very quiet
• literally: night very quiet

This is completely normal in Vietnamese. Adjectives can function like predicates on their own.

Compare:

• Trời nóng. = The weather is hot.
• Cô ấy đẹp. = She is beautiful.

You only use là in different situations, such as identification or definition, not simple adjective descriptions.

Rất means very.

In Vietnamese, it usually goes before the adjective:

• rất yên tĩnh = very quiet
• rất đẹp = very beautiful
• rất lạnh = very cold

So the structure here is:

• Đêm = night
• rất = very
• yên tĩnh = quiet

That gives: The night is very quiet.

It is written as two separate syllables: yên tĩnh.

That is normal in Vietnamese. Many Vietnamese words, especially descriptive ones, are made of two syllables written with a space between them. Even though there is a space, learners often treat yên tĩnh as a single vocabulary item meaning quiet or peaceful/quiet in atmosphere.

So you should learn yên tĩnh together as one expression.

Both relate to nighttime, but they are not always interchangeable.

• đêm = night, especially the period of the night itself
• tối = evening or tonight, depending on context

Examples:

• ban đêm = at night
• đêm nay = tonight
• buổi tối = evening
• tối nay = tonight

So in Đêm rất yên tĩnh, đêm is the natural choice because the sentence is talking about the night as a time/atmosphere.

Vietnamese does not use articles the same way English does. There is no direct equivalent of a/an/the that must appear before nouns in ordinary sentences.

So:

• Đêm rất yên tĩnh can mean The night is very quiet
• depending on context, it could also feel like Night is very quiet or The nighttime is very quiet

English requires an article in many cases, but Vietnamese usually does not.

If you want to make the noun more specific, Vietnamese often uses other words, for example:

• Đêm nay rất yên tĩnh. = Tonight is very quiet.
• Đêm đó rất yên tĩnh. = That night was very quiet.

A rough pronunciation guide for English speakers:

• Đêm ≈ dem / dyem with a level tone
• rất ≈ zut in Northern Vietnamese, often closer to yut or zut depending on accent, with a sharp rising/glottal tone
• yên ≈ yen with a level tone
• tĩnh ≈ something like ting with a dipping/glottal tone

A few important notes:

• đ is not the same as d in Vietnamese. đ sounds like English d.
• The tones matter a lot.
• Pronunciation differs between Northern and Southern accents, especially for r and some tones.

If you are learning the Northern standard, pay special attention to the tones on:

• rất
• tĩnh

Usually, yes: yên tĩnh means quiet, peaceful, or still in the sense of a calm environment.

It often describes places, times, or surroundings:

• căn phòng yên tĩnh = a quiet room
• khu phố yên tĩnh = a quiet neighborhood
• đêm yên tĩnh = a quiet night

It is not usually the best choice for telling a person to be quiet. For that, Vietnamese more often uses expressions like:

• Im lặng! = Be quiet!
• Yên lặng! = Silence!/Be quiet!

So yên tĩnh is more about the atmosphere being calm and quiet.

Yes, absolutely.

• Đêm yên tĩnh. = The night is quiet.
• Đêm rất yên tĩnh. = The night is very quiet.

Adding rất just increases the intensity.

In everyday Vietnamese, rất is extremely common before adjectives, but it is not required.

Very often, yes.

A common pattern is:

• noun + rất + adjective

Examples:

• Trời rất đẹp. = The weather is very beautiful.
• Căn phòng rất nhỏ. = The room is very small.
• Con đường rất vắng. = The street is very empty/deserted.

So Đêm rất yên tĩnh follows a very common Vietnamese sentence pattern.

Sometimes, depending on context, but the most direct reading is The night is very quiet.

If you specifically want At night it is very quiet, Vietnamese would more naturally use something like:

• Ban đêm rất yên tĩnh.
• Vào ban đêm, rất yên tĩnh.

So đêm by itself here is more naturally understood as the night, not as a general adverbial phrase meaning at night.

Yes, this is natural Vietnamese.

It is a simple, normal descriptive sentence. It sounds literary or observational depending on context, but not unnatural.

For example, it could appear in:

• a story: Đêm rất yên tĩnh. Không ai nói gì.
• conversation: Hôm nay lạ thật, đêm rất yên tĩnh.
• descriptive writing about weather, atmosphere, or mood

So this is a useful real sentence pattern to learn.