Ilma on kaunis tänään.

That is a very common question. Ilma can mean air, weather, or atmosphere, depending on context.

In this sentence, ilma refers to the weather/air outside. So the sentence is talking about how pleasant it is outdoors.

However, for everyday weather, sää is often the more common neutral word:

• Sää on kaunis tänään. = The weather is beautiful today.

Using ilma is still understandable, but it can sound a bit more:

• literary
• descriptive
• old-fashioned in some contexts
• focused on the feel of the air/outdoors rather than just weather conditions

So ilma is not wrong here; it just has a slightly different flavor from sää.

On is the third-person singular form of the verb olla, which means to be.

So:

• minä olen = I am
• sinä olet = you are
• hän on = he/she is
• ilma on = the weather/air is

In this sentence, on simply means is.

Finnish usually does not use articles like a, an, or the.

So:

• ilma can mean air, the air, weather, or the weather
• the exact meaning depends on context

That is why Ilma on kaunis tänään can naturally mean The weather is beautiful today even though there is no separate word for the.

This is normal Finnish grammar, not something missing from the sentence.

Because this sentence uses predicate adjective structure:

• Ilma on kaunis. = The weather is beautiful.

Here, kaunis comes after the verb on, just like English beautiful comes after is.

If you put the adjective before the noun, it becomes part of a noun phrase:

• kaunis ilma = beautiful weather / beautiful air

So compare:

• Ilma on kaunis. = The weather is beautiful.
• Tänään on kaunis ilma. = Today there is beautiful weather / It is beautiful weather today.

Both are possible, but they are built differently.

Kaunis is in its basic dictionary form here because it is a predicate adjective with a singular subject.

The subject is:

• ilma = singular

So the adjective stays in the basic singular form:

• ilma on kaunis

A beginner does not need to think about any special ending here. This is the normal form you would expect in a simple sentence like this.

Tänään is an adverb of time, meaning today.

It tells you when something is true:

• Ilma on kaunis tänään. = The weather is beautiful today.

For a beginner, the easiest way to treat tänään is simply as a fixed adverb meaning today. You do not usually need to break it apart or change it in this kind of sentence.

Yes, Finnish word order is fairly flexible.

The sentence:

• Ilma on kaunis tänään.

is a normal, natural way to say it. But you can also move tänään:

• Tänään ilma on kaunis.
• Ilma on tänään kaunis.

These all mean roughly the same thing, but the emphasis changes a little.

Very roughly:

• Ilma on kaunis tänään. = neutral statement
• Tänään ilma on kaunis. = emphasis on today
• Ilma on tänään kaunis. = also highlights today, often with a slightly more contrastive feel

English depends more on fixed word order; Finnish uses word order more for emphasis and information structure.

Yes, it is understandable and grammatical.

That said, many Finnish speakers might more naturally say one of these:

• Sää on kaunis tänään.
• Tänään on kaunis ilma.
• Tänään on kaunis sää.

Why? Because:

• sää is often the most everyday word for weather
• kaunis ilma is a very common phrase for beautiful weather

So your sentence is fine, but it may sound a little more descriptive or less everyday than some alternatives.

Yes, Finnish does use kaunis about weather.

In this context, kaunis means something like:

• beautiful
• lovely
• nice
• pleasant

So kaunis ilma or ilma on kaunis is completely understandable.

Depending on context, Finnish speakers might also use words like:

• hyvä = good
• upea = शानदार / magnificent
• ihana = lovely
• aurinkoinen = sunny

But kaunis is a perfectly normal descriptive choice.

Ilma is in the nominative singular, which is the basic form of the noun.

Here it is the subject of the sentence:

• Ilma = the weather/air
• on = is
• kaunis = beautiful
• tänään = today

So from a grammar point of view:

• ilma = subject, nominative singular

This is exactly what you would expect in a simple sentence like this.

A simple pronunciation guide would be:

Ilma on kaunis tänään
≈ EEL-ma on KAU-nis TAN-aan

A few helpful notes:

• i is like ee in see
• au sounds like the ow in cow
• ä is a front vowel, somewhat like the a in British cat, but cleaner and shorter
• ään has a long ä sound, because ää is long

Finnish pronunciation is usually very regular, so once you know the sounds, it is much easier than English spelling.

No, not in a normal present-tense sentence like this.

Finnish usually does require the verb olla (to be) in sentences like:

• Ilma on kaunis.
• Talo on iso.
• Hän on väsynyt.

So you should not say:

• Ilma kaunis tänään ✗

You need:

• Ilma on kaunis tänään. ✓

That is one important difference from some languages that allow the verb to be to be omitted in the present tense.