Quand je contemple chaque étoile, j’imagine des univers infinis.

Both quand and lorsque can mean when.

In this sentence, quand is the most natural, everyday choice. Lorsque is a bit more formal or literary. Since the sentence already has a poetic tone, either could work, but quand still sounds perfectly good and natural.

So:

• Quand je contemple chaque étoile... = natural and common
• Lorsque je contemple chaque étoile... = slightly more formal/literary

French usually avoids having two vowel sounds next to each other when possible. Since imagine begins with a vowel sound, je contracts to j’.

So:

• je contemple
• j’imagine

This happens with many verbs:

• j’aime
• j’écoute
• j’adore
• j’habite

It is the same basic idea as in English contractions, though in French it is often required.

French often uses the present tense to express:

• something happening now
• a general truth
• a habitual or repeated action

Here, the sentence sounds like a general or repeated experience: When I contemplate each star, I imagine infinite universes.

So the present tense works naturally for both actions:

• je contemple
• j’imagine

French does this just like English often does in sentences with when:

• When I read, I relax.
• Quand je lis, je me détends.

Chaque means each or every, and it focuses on the stars one by one.

So:

• chaque étoile = each star / every star
• toutes les étoiles = all the stars

The difference is subtle but important:

• Je contemple chaque étoile suggests considering stars individually.
• Je contemple toutes les étoiles suggests the whole group together.

In this sentence, chaque étoile fits the reflective, poetic tone very well.

Because chaque is followed by a singular noun in French.

So you say:

• chaque étoile
• chaque livre
• chaque jour

Even though the meaning can be like every star, the noun stays singular.

This is similar to English:

• every star not
• every stars

French usually needs an article before a countable noun. Here, univers is a plural countable noun, so des is used.

• un univers = a universe
• des univers = some universes / universes

After imaginer, French normally keeps the article:

• j’imagine un monde
• j’imagine des possibilités
• j’imagine des univers infinis

English often drops the article in more general statements, but French usually does not.

Infinis is an adjective describing univers.

Two things are happening:

1. Position
   In French, many adjectives come after the noun, and infini usually does:

   • un univers infini
   • des univers infinis

2. Agreement
   Adjectives must agree with the noun they describe.

   • univers is plural
   • so infini becomes infinis

If the noun were feminine singular, it would change differently:

• une étendue infinie

The comma separates the introductory clause from the main clause:

• Quand je contemple chaque étoile, ...
• j’imagine des univers infinis.

It works much like English:

• When I look at each star, I imagine infinite universes.

The comma is helpful and very natural here, especially because the first clause comes before the main idea.

Contempler is more thoughtful, deep, and sustained than regarder.

• regarder = to look at
• contempler = to contemplate, gaze at, look at deeply or thoughtfully

So:

• Quand je regarde chaque étoile... sounds simpler and more everyday.
• Quand je contemple chaque étoile... sounds more poetic, reflective, and emotional.

That choice helps create the tone of the sentence.

Étoile is pronounced roughly like ay-twal.

The accent in é matters:

• é gives a clear ay sound
• without the accent, the pronunciation rules would be different

So étoile begins with a vowel sound, which is one reason the sentence flows smoothly after chaque.

Also, remember that étoile is feminine:

• une étoile
• chaque étoile

Some French nouns already end in -s in the singular, and their plural form is written the same way.

So:

• un univers
• des univers

The article tells you whether it is singular or plural.

This is similar to a few English words whose form does not change much, though in French it is a normal pattern for certain nouns.

Yes, depending on context, quand can sometimes feel like when or whenever.

In this sentence, the present tense gives it a habitual or general feeling, so English might understand it as:

• When I contemplate each star...
• Whenever I contemplate each star...

Both ideas are close. The French does not need a separate word here to create that repeated/habitual sense; the context and present tense already do a lot of that work.