Learn Hardcore Finnish: Teleskooppi näyttää, kuinka pieni planeetta on verrattuna koko galaksiin. - The telescope shows how small a planet is compared to the whole galaxy.

“to show” (transitive)
- Pattern: näyttää + object / content clause
- Example: Teleskooppi näyttää, kuinka pieni planeetta on…
  → The telescope shows how small the planet is…
“to seem / to appear” (intransitive)
- Pattern: näyttää + adjective / noun in ablative (-lta/-ltä)
- Example: Hän näyttää väsyneeltä.
  → He/She seems tired.

In your sentence it is the first meaning: “to show”.

What is the role of the clause kuinka pieni planeetta on verrattuna koko galaksiin in the sentence?

That whole piece is a content clause (a kind of object clause) that tells what the telescope shows.

Main clause: Teleskooppi näyttää
→ The telescope shows
Content clause: kuinka pieni planeetta on verrattuna koko galaksiin
→ how small the planet is compared to the whole galaxy

So grammatically, this clause functions as the object/complement of näyttää.

Why is there a comma before kuinka in Teleskooppi näyttää, kuinka pieni…?

In Finnish, a comma is normally used between a main clause and a subordinate clause, even when English would not have one.

Main clause: Teleskooppi näyttää
Subordinate clause: kuinka pieni planeetta on verrattuna koko galaksiin

Rule of thumb: if you can split the sentence into “independent sentence + että/kuinka/miten/koska/jos…”, Finnish usually puts a comma there:

Tiedän, että se on totta. – I know (that) it is true.
En ymmärrä, miksi hän lähti. – I don’t understand why he left.

What exactly does kuinka do here, and how is it different from miten?

Here kuinka means “how” in the sense of “to what degree / how much” and it introduces the subordinate clause:

kuinka pieni planeetta on
→ how small the planet is

About kuinka vs miten:

Both can mean “how”.
When they modify an adjective/adverb of degree, as here, both are possible:
- kuinka pieni planeetta on
- miten pieni planeetta on
kuinka often sounds a bit more neutral or written,
miten a bit more colloquial / everyday.

So you could say:

Teleskooppi näyttää, miten pieni planeetta on verrattuna koko galaksiin.

This is also correct and natural.

Why is the word order kuinka pieni planeetta on and not kuinka planeetta on pieni?

The usual Finnish pattern is:

kuinka + adjective + subject + verb
→ kuinka pieni planeetta on

Here kuinka directly modifies pieni, which is the info we care about (the degree of smallness).

Other possible orders:

kuinka pieni on planeetta – also grammatical, but with a slight emphasis on planeetta (“how small the planet is (as opposed to something else)”).
kuinka planeetta on pieni – this is not natural; Finnish doesn’t normally split kuinka from the adjective it modifies like that.

So kuinka pieni planeetta on is the default, most natural order.

What form is verrattuna, and what does it mean literally?

Verrattuna comes from the verb verrata (to compare).

Base: verrata
Past passive participle: verrattu (compared)
Inessive singular: verrattuna (when in a compared state)

It’s used like an adverbial participle and is usually translated as “(when) compared (to)”:

pieni verrattuna koko galaksiin
→ small when compared to the whole galaxy
→ small compared to the whole galaxy

It is not a finite verb here; the finite verb in that clause is on (is).

What case is galaksiin, and why is that form used?

Galaksiin is in the illative singular (the “into / to” case).

Stem: galaksi-
Illative ending: -in
Because the stem already ends in i, you get galaksi + in → galaksiin.

The reason for this case: Finnish often uses the illative with comparisons built from verrata / verrattuna:

verrata johonkin – to compare to something
verrattuna johonkin – when compared to something

So:

verrattuna koko galaksiin
→ compared to the whole galaxy

The illative marks the target of the comparison.

Why is planeetta in its basic form and not something like planeetan?

Planeetta is in the nominative singular because it is the subject of the verb on (is) inside the subordinate clause:

(kuinka) pieni planeetta on (verrattuna…)
→ how small the planet is (compared to…)

The pattern is the same as a simple sentence:

Planeetta on pieni. – The planet is small.

So we keep the subject planeetta in nominative, not in genitive or any other case.

What is the function of koko in verrattuna koko galaksiin, and why doesn’t it seem to change form?

Koko here means “the whole / entire”:

galaksi – galaxy
koko galaksi – the whole galaxy

In koko galaksiin the case ending -iin (illative) is attached to the noun:

koko + galaksi + in → koko galaksiin

Koko itself often stays in a “bare” form and the following noun carries the case ending, which is normal:

koko talossa – in the whole house
koko kaupungista – from the whole city
koko galaksiin – into / to the whole galaxy

So koko is functioning like a quantifier (“whole”), and the noun galaksi shows the case.

Could we say galaksiin verrattuna instead of verrattuna koko galaksiin? Does the position matter?

Yes, Finnish allows some flexibility in the position of the verrattuna + johonkin phrase.

All of these are grammatically fine:

kuinka pieni planeetta on verrattuna koko galaksiin
kuinka pieni planeetta on koko galaksiin verrattuna

The meaning is the same: how small the planet is compared to the whole galaxy.

Putting verrattuna at the end (…koko galaksiin verrattuna) is very common and might even be slightly more natural in speech, because the comparison target comes immediately before the “compared to” element, like English “to the whole galaxy compared”.

Can we leave out on and just say kuinka pieni planeetta verrattuna koko galaksiin?

No – on is required here.

The clause kuinka pieni planeetta on verrattuna koko galaksiin is structurally just a normal sentence:

Planeetta on pieni verrattuna koko galaksiin.
→ The planet is small compared to the whole galaxy.

When it becomes an embedded clause after kuinka, it still needs a finite verb:

kuinka pieni planeetta on verrattuna koko galaksiin
→ how small the planet is compared to the whole galaxy

If you remove on, it becomes ungrammatical, because Finnish doesn’t allow you to drop the copula in this kind of clause.

Is there any difference in meaning between kuinka pieni planeetta on verrattuna koko galaksiin and kuinka pieni planeetta on koko galaksiin verrattuna?

The meaning is basically the same; both mean:

how small the planet is compared to the whole galaxy.

The difference is only a matter of word order and rhythm:

…on verrattuna koko galaksiin
– Slightly more “bookish” in feel; the verrattuna phrase comes directly after on.
…on koko galaksiin verrattuna
– Very natural especially in speech; the comparison target (koko galaksiin) directly precedes verrattuna, much like English “compared to the whole galaxy.”

Both are good, correct Finnish.