La galaksio estas parto de la universo.

Yes. La is the Esperanto definite article, equivalent to English the.

So:

• la galaksio = the galaxy
• la universo = the universe

A few useful points:

• La never changes form.
• Esperanto has no indefinite article, so a galaxy would simply be galaksio.
• You use la when the thing is definite or understood.

In this sentence, both the galaxy and the universe are treated as definite.

Because the universe is a specific, unique thing, so Esperanto normally uses la here: la universo.

Without la, universo would sound more like a universe or universe in a more general sense, depending on context.

So:

• la universo = the universe
• universo = a universe or universe in general

Because -o is the standard noun ending in Esperanto.

That means:

• galaksio = galaxy
• parto = part
• universo = universe

This is one of the most regular features of Esperanto: you can often tell a word’s job just from its ending.

Some common endings are:

• -o = noun
• -a = adjective
• -e = adverb
• -i = infinitive verb

Estas is the present-tense form of esti, meaning to be.

So:

• mi estas = I am
• vi estas = you are
• li/ŝi/ĝi estas = he/she/it is
• ili estas = they are

Unlike English, the verb does not change depending on the subject. It is always estas in the present tense.

So La galaksio estas... means The galaxy is...

Because Esperanto commonly expresses part of something with:

parto de + noun

So:

• parto de la universo = part of the universe
• parto de la libro = part of the book
• parto de la urbo = part of the city

This is a very normal structure in Esperanto.

Here, de means of.

So:

• parto de la universo = part of the universe

More broadly, de is a very common preposition that can show relationships like:

• possession: la libro de Maria = Maria’s book / the book of Maria
• origin/source: mi venas de Londono = I come from London
• composition or relation in some contexts

In this sentence, it marks the whole that the part belongs to.

Because there is no direct object here.

The sentence has this structure:

• La galaksio = subject
• estas = linking verb
• parto de la universo = predicate complement

After esti (to be), Esperanto normally does not use the accusative -n for the complement.

So parto stays parto, not parton.

A quick comparison:

• La galaksio estas parto de la universo. = The galaxy is part of the universe.
• Mi vidas la galaksion. = I see the galaxy.

In the second sentence, galaksion gets -n because it is the direct object of vidas.

Yes. La galaksio is the subject.

You can identify it as the thing being described. The sentence tells us something about the galaxy: that it is part of the universe.

So the structure is:

• La galaksio = subject
• estas = verb
• parto de la universo = description of the subject

Yes, Esperanto word order is fairly flexible, though the most neutral order is the one given:

La galaksio estas parto de la universo.

You could also say:

• Parto de la universo estas la galaksio.

But that sounds more marked or stylistically different, as if emphasizing part of the universe first.

For learners, it is best to stick with the normal order:

subject + verb + complement

A helpful approximation is:

ga-lak-SI-o

Esperanto stress normally falls on the second-to-last syllable, so the stress is on si.

Also:

• g is always hard, as in go
• a is like a in father
• ks sounds like English x in many words
• io is two vowel sounds, not one merged sound

So galaksio has four syllables: ga-la-ksi-o

A good approximation is:

u-ni-VER-so

Again, the stress is on the second-to-last syllable, so ver is stressed.

Syllables: u-ni-ver-so

This regular stress rule is very useful in Esperanto.

Usually, parto de la universo is the most natural expression for part of the universe.

De is the standard choice after parto.

Using el can sometimes suggest out of or from among, which is a slightly different nuance. So for a simple statement like this, de is the best and most idiomatic option.

Because here the word means galaxy, which is a noun.

If you wanted related forms, Esperanto can build them very regularly:

• galaksio = galaxy
• galaksia = galactic
• galaksie = galactically

That regular word-building system is one of Esperanto’s main features.

Yes, slightly.

• La galaksio = the galaxy
• Tiu galaksio = that galaxy

Tiu points to a specific one, often contrasting it with others.

So:

• La galaksio estas parto de la universo. = The galaxy is part of the universe.
• Tiu galaksio estas parto de la universo. = That galaxy is part of the universe.

The grammar is similar, but tiu adds a demonstrative meaning.

Yes. It is complete, grammatical, and natural.

It has everything a basic Esperanto sentence needs:

• a subject: La galaksio
• a verb: estas
• a complement: parto de la universo

It is a good example of a simple identifying/describing sentence in Esperanto.