Nous voyons la lune.

Because the subject is nous (we), and French verbs change form depending on the subject.

The verb here is voir (to see). In the present tense:

• je vois
• tu vois
• il / elle / on voit
• nous voyons
• vous voyez
• ils / elles voient

So with nous, you need voyons.

One useful thing to notice is that nous forms often help show the stem clearly in French verbs.

Voyons is pronounced roughly like vwah-yon, but with a nasal ending.

More exactly:

• voy- sounds like vwah-y
• -ons sounds like on in French, with a nasal vowel
• the final s is silent

So the whole word is approximately /vwajɔ̃/.

A native English speaker should also notice that the y in voyons is pronounced; it is not silent.

Yes, several letters are silent, which is very common in French.

• Nous → pronounced /nu/
  The final s is silent.
• voyons → pronounced /vwajɔ̃/
  The final s is silent.
• la → pronounced /la/
• lune → pronounced /lyn/
  The final e is silent.

So although the sentence has more written letters than you might expect, not all of them are pronounced.

Because lune is a feminine noun in French.

French nouns have grammatical gender, so the changes depending on whether the noun is masculine or feminine:

• le for masculine singular
• la for feminine singular
• l' before a vowel sound
• les for plural

Since lune is feminine, it takes la: la lune.

This grammatical gender is something you usually have to learn along with each noun.

In French, nouns very often appear with an article, much more consistently than in English.

Here, lune is a specific thing, so French uses the definite article la.

In this sentence, la lune is the normal way to say it. Saying just lune by itself would usually sound incomplete in a sentence like this.

Yes. In everyday spoken French, on is very often used instead of nous to mean we.

So both are possible:

• Nous voyons la lune → more formal, more careful, more typical of writing or formal speech
• On voit la lune → very common in everyday conversation

For learners, it is important to know both, because nous is standard grammar, but on is extremely common in real life.

It can mean both, depending on context.

French present tense often covers both:

• we see
• we are seeing

So Nous voyons la lune could mean either of those in English. French usually does not need a separate form like English are seeing unless there is a special reason to emphasize the ongoing action.

Yes, in this basic sentence it is very similar.

The order is:

• Nous = subject
• voyons = verb
• la lune = direct object

So it follows the pattern:

subject + verb + object

That is one reason this sentence feels relatively straightforward to English speakers.

Voir means to see, while regarder means to look at or to watch.

• voir = perceiving something with your eyes
• regarder = actively directing your eyes toward something

So:

• Nous voyons la lune = we can see the moon
• Nous regardons la lune = we are looking at the moon

In many situations, both could make sense, but they are not exactly the same idea.

Because l' is used before a word that starts with a vowel sound or a silent h.

Examples:

• l'arbre
• l'école
• l'homme

But lune starts with the consonant sound l, so you keep la:

• la lune

No. There is no liaison here.

Liaison happens when a normally silent final consonant is pronounced before a following word that begins with a vowel sound or silent h.

But voyons begins with v, a consonant sound, so the s in nous stays silent:

• nous voyons → /nu vwajɔ̃/

So you do not say a z sound between the two words.

Yes. Voyons ! can also be used as a separate expression in French.

Depending on tone and context, it can mean things like:

• let’s see
• come now
• really now
• come on

But in Nous voyons la lune, it is simply the normal verb form of voir with nous.