Himmelen er grå.

Because himmelen is the definite form of the noun, meaning the sky.

• himmel = sky / a sky
• himmelen = the sky

In Norwegian, the definite article is often added to the end of the noun as a suffix instead of being a separate word.

The ending -en is the usual definite singular ending for many common gender nouns in Bokmål.

So:

• en himmel = a sky
• himmelen = the sky

This is a very common pattern in Norwegian:

• en bil → bilen
• en stol → stolen
• en himmel → himmelen

Because Norwegian usually expresses the by attaching it to the noun.

In English:

• the sky

In Norwegian:

• himmelen

This is one of the biggest differences from English. Norwegian does have structures where a separate determiner appears too, but in a simple sentence like this, the suffixed form is the normal one.

Er means is / am / are.

It is the present tense of the verb å være (to be).

Examples:

• jeg er = I am
• du er = you are
• han er = he is
• himmelen er grå = the sky is gray

Unlike English, Norwegian does not change the present-tense form depending on the subject. It stays er for everyone.

Here grå is a predicative adjective, meaning it comes after er and describes the subject.

In this sentence, the basic form grå is correct.

You can think of it like this:

• Himmelen er grå. = The sky is gray.

With some other noun types, adjectives can change form:

• Huset er grått. = The house is gray.
  (hus is neuter, so the adjective becomes grått)

So grå stays as it is here because himmelen is not a neuter singular noun.

Himmel is a common gender noun in Bokmål.

That is why you get:

• en himmel
• himmelen

Norwegian nouns are mainly:

• common gender
• neuter

Knowing the gender helps you choose the right article and endings.

Yes, in this simple statement the word order is very similar to English:

• Himmelen = subject
• er = verb
• grå = adjective/complement

So the structure is:

Subject + verb + description

That makes Himmelen er grå. very straightforward for an English speaker.

The letter å is pronounced like the vowel in English law, saw, or more in many accents.

So grå sounds roughly like graw.

A rough guide:

• grå ≈ graw

Also:

• Himmelen is roughly HIM-me-len
• er is often pronounced very lightly in normal speech

The most important new sound here for many learners is å.

Yes. Skyen er grå also means the sky is gray.

But there is a slight difference in feel:

• himmel often refers to the sky/heavens
• sky can mean cloud, and skyen usually means the cloud

So Himmelen er grå is the natural choice for the sky is gray.
Skyen er grå would more naturally mean the cloud is gray.

Yes, very often.

When you describe something with to be, Norwegian commonly uses:

noun + er + adjective

Examples:

• Bilen er rød. = The car is red.
• Huset er stort. = The house is big.
• Himmelen er grå. = The sky is gray.

So this sentence follows a very common and useful pattern.