Månen er usynlig.

Because -en is the definite article attached to the noun.

• måne = moon / a moon
• månen = the moon

So Månen er usynlig means The moon is invisible.

This is very common in Norwegian: instead of putting a separate word for the before the noun, Norwegian often adds the article to the end of the noun.

• bok = book
• boken = the book

Måne is usually masculine in Bokmål.

That is why the definite singular form is månen:

• en måne = a moon
• månen = the moon

Yes, gender matters because it affects articles and some adjective forms in other contexts.

Er is the present tense of å være, which means to be.

So:

• å være = to be
• er = is / am / are

In this sentence:

• Månen = the moon
• er = is
• usynlig = invisible

So the structure is simply subject + verb + adjective.

Because usynlig is the correct form for an adjective used:

1. after the verb er, and
2. with a singular noun.

Here, månen is singular, so:

• Månen er usynlig. = The moon is invisible.

You would see usynlige with plural subjects:

• Stjernene er usynlige. = The stars are invisible.

It is built from:

• synlig = visible
• u- = a prefix meaning un- or not

So:

• synlig = visible
• usynlig = invisible

This prefix works like English un- in many words.

Yes, in this simple statement it is very similar to English:

• Månen = subject
• er = verb
• usynlig = adjective/complement

So:

• Månen er usynlig.
• The moon is invisible.

The basic pattern is:

subject + verb + description

In Norwegian, yes/no questions usually use verb before subject.

Statement:

• Månen er usynlig. = The moon is invisible.

Question:

• Er månen usynlig? = Is the moon invisible?

So the word order changes from:

• subject + verb to
• verb + subject

A helpful approximate pronunciation is:

• månen ≈ MOH-nen

A few notes:

• å sounds like a broad vowel, roughly like the vowel in British more for many learners, though not exactly.
• The n at the end is clearly pronounced.
• Stress is on the first syllable: MÅ-nen

A rough guide is:

• usynlig ≈ oo-SUUN-lee or oo-SIN-lee, depending on how closely you are trying to match Norwegian sounds

Important sound notes:

• u is not exactly the English oo, but that approximation helps at first.
• y is a Norwegian vowel that English does not really have. It is one of the trickier sounds for English speakers.
• The g at the end of -lig is often weak or not fully pronounced in everyday speech.

So learners often hear something close to u-SYN-li.

Yes, but it means something different.

• Månen er usynlig. = The moon is invisible.
• En måne er usynlig. = A moon is invisible.

The first one refers to a specific moon, most naturally the moon.
The second sounds more general or less natural unless you are talking about one moon among others in a special context.

So for the usual meaning, månen is the natural choice.

It is capitalized because it is the first word of the sentence, not because it is a noun.

In Norwegian, common nouns are not normally capitalized the way they are in German.

So:

• månen in the middle of a sentence would normally be lowercase.
• Månen is capitalized here only because it begins the sentence.