أرى النجوم في الليل.

A fully vowelled version is أَرَى النُّجُومَ فِي اللَّيْلِ.

A rough pronunciation is ʾarā an-nujūma fī al-layli.
In connected speech, the definite article changes in pronunciation before certain letters, so you will hear the n and l sounds doubled.

Because أرى already includes the subject I.

In the present/imperfect tense, Arabic verbs often show the subject inside the verb itself. The prefix أ- here marks first person singular, so أرى means I see or I am seeing.

You can add أنا if you want emphasis:

أنا أرى النجوم في الليل = I see the stars at night

But it is not necessary.

أرى is the present/imperfect form of the verb رأى = to see.

This verb is somewhat irregular because it is a weak verb. In this form, the last sound is a long ā, and Arabic writes that here with ى (alif maqṣūra).

So:

• رأى = he saw
• أرى = I see / I am seeing

It can mean either one, depending on context.

The Arabic imperfect tense often covers both:

• I see
• I am seeing
• sometimes even a habitual sense like I usually see

In this sentence, the most natural meaning is probably a general or habitual one: I see the stars at night.

No. النجوم is a broken plural.

The singular is نجم = star.
Its plural is نجوم = stars.

Arabic has many broken plurals, where the inside pattern of the word changes instead of just adding a regular ending.

Yes, literally it is the stars.

But Arabic often uses the definite article in places where English would use a general plural with no article. So النجوم can mean the stars in a broad, general sense, not necessarily a specific set already mentioned.

That is very normal in Arabic.

In fully vocalized MSA:

• النُّجُومَ is accusative because it is the direct object of أرى
• اللَّيْلِ is genitive because it comes after the preposition في

So the structure is:

• أرى = verb
• النجومَ = direct object
• في الليلِ = prepositional phrase

In normal everyday writing, these short vowel endings are usually not written.

Because Arabic often uses في with time expressions in ways that English translates as in, at, or during, depending on what sounds natural.

So:

• في الليل literally = in the night
• natural English = at night

This is a very common kind of difference between languages.

Both words begin with sun letters, so the ل of ال assimilates to the next consonant.

• النجوم begins with ن, so it is pronounced an-nujūm
• الليل begins with ل, so the l sound is doubled: al-layl

That is why, in full vocalization, you see a shadda:

• النُّجُوم
• اللَّيْل

So the spelling keeps ال, but the pronunciation changes.

Yes.

أرى النجوم في الليل is a normal verb-initial sentence in Arabic. But Arabic word order is flexible, so you can move parts of the sentence for emphasis.

For example:

• في الليل أرى النجوم = At night, I see the stars
• أنا أرى النجوم في الليل = I see the stars at night with extra emphasis on I

The core meaning stays the same, but the focus can shift.