Η θερμοκρασία είναι μηδέν.

Η is the feminine singular definite article, so it means the.

It appears here because θερμοκρασία is a feminine singular noun:

• η θερμοκρασία = the temperature

Greek nouns have grammatical gender, and the article must match the noun in:

• gender
• number
• case

Since θερμοκρασία is feminine singular nominative here, the correct article is η.

In Greek, nouns belong to grammatical gender classes, and that does not mean the thing itself is biologically feminine or masculine.

Θερμοκρασία is feminine because that is simply its grammatical gender. Many nouns ending in -ία are feminine.

So you should learn it as a unit:

• η θερμοκρασία

This is very common in Greek: you usually memorize a noun together with its article.

A rough pronunciation guide is:

ee ther-mo-kra-SEE-a EE-ne mee-THEN

A few helpful notes:

• η sounds like ee
• θ sounds like the th in think
• σία in θερμοκρασία is stressed on the last -σία
• είναι is pronounced EE-ne
• δ in Modern Greek sounds like the th in this
• so μηδέν sounds like mee-THEN

The stress marks are important:

• θερμοκρασία
• είναι
• μηδέν

Είναι means is here. It is the 3rd person singular form of the verb είμαι, which means to be.

So:

• είμαι = I am
• είσαι = you are
• είναι = he/she/it is

In this sentence:

• Η θερμοκρασία είναι μηδέν.
• literally: The temperature is zero.

Greek usually does not need an explicit subject pronoun when the subject is already stated or clear from context.

Here, the subject is already present:

• Η θερμοκρασία = the temperature

So Greek does not need anything like:

• The temperature, it is zero

That would be unnecessary in normal Greek.

More generally, Greek often drops subject pronouns because the verb form already gives useful information.

Because μηδέν is functioning as the complement after είναι. In English, we also say:

• The temperature is zero not
• The temperature is the zero

So Greek works similarly here:

• Η θερμοκρασία είναι μηδέν.

Μηδέν is a number, and after είναι it does not need an article in this sentence.

Here μηδέν is the number zero.

In Greek, μηδέν can behave a bit like a numeral, and in many contexts it stays the same form. In this sentence, you can think of it simply as the number used after είναι:

• is zero

So for a learner, the most useful takeaway is:

• μηδέν = zero
• in this sentence, it does not change form

Yes. Η θερμοκρασία is the subject of the sentence, so it is in the nominative case.

After the verb είναι, the complement is also typically nominative in Greek when appropriate. Since μηδέν is a numeral and basically indeclinable here, you do not see a case ending on it.

So:

• Η θερμοκρασία = nominative subject
• είναι = copular verb
• μηδέν = complement

Yes, Greek word order is more flexible than English, but not every variation sounds equally natural in every context.

The neutral, straightforward order is:

• Η θερμοκρασία είναι μηδέν.

You could change the order for emphasis, but it may sound marked or literary.

For example, Greek often changes word order to emphasize a particular part of the sentence. Still, for a basic learner, the best pattern to remember is:

subject + είναι + complement

So:

• Η θερμοκρασία είναι μηδέν.

It is grammatical and clear, but in everyday speech, especially when talking about weather, Greeks may often say something more idiomatic, such as:

• Η θερμοκρασία είναι στο μηδέν. = The temperature is at zero.
• Έχει μηδέν βαθμούς. = It is zero degrees.

So your sentence is correct, but it can sound a bit more direct or formal depending on context.

A useful distinction:

• Η θερμοκρασία είναι μηδέν. = perfectly understandable, somewhat plain or technical
• Η θερμοκρασία είναι στο μηδέν. = very natural in weather contexts

This is a very common beginner question.

• η without an accent = the for feminine singular nouns
• ή with an accent = or

So:

• η θερμοκρασία = the temperature
• καφές ή τσάι = coffee or tea

The accent helps distinguish two different words that would otherwise look the same.

Yes, that is a very good habit.

Instead of learning only:

• θερμοκρασία

learn:

• η θερμοκρασία

That helps you remember:

• the noun’s gender
• the correct article
• how it will behave in sentences

This is one of the best ways to build Greek vocabulary efficiently.

Yes. Μηδέν is used in many common contexts, for example:

• numbers
• scores
• temperatures
• abstract expressions

Examples:

• μηδέν βαθμοί = zero degrees
• δύο μηδέν = two nil / two to zero
• ξεκινάμε από το μηδέν = we start from zero

So this word is very useful and worth learning early.