La planedo moviĝas laŭ la orbito.

Because movi is usually transitive: it means to move something.

• Mi movas la seĝon. = I move the chair.
• La planedo moviĝas. = The planet moves.

The ending -iĝ- often makes a verb intransitive or gives the sense of undergoing a change/state. So:

• movi = to move something
• moviĝi = to move, to become moved

So in La planedo moviĝas, the planet is not moving another object; it itself is in motion.

moviĝas can be divided into:

• mov- = move
• -iĝ- = become / get / undergo / intransitive-forming element
• -as = present tense

So moviĝas literally has the idea of is moving / becomes moved.

This is a very common Esperanto pattern. For example:

• fermi = to close something
• fermiĝi = to close, to become closed

Because la planedo is the subject of the sentence, not the direct object.

In Esperanto, the -n ending marks the direct object (and sometimes direction). Here, the planet is the thing doing the action:

• La planedo moviĝas... = The planet moves...

So planedo stays without -n.

Because la orbito comes after the preposition laŭ, and prepositions normally take the basic form, not the accusative.

So:

• laŭ la orbito = along the orbit

Also, this phrase is not a direct object. It tells us how/where the movement happens.

Here laŭ means along or following.

So laŭ la orbito means the planet moves along the orbit, following its path.

Be careful: laŭ can also mean according to, depending on context.

For example:

• La trajno veturas laŭ la rivero. = The train travels along the river.
• Laŭ mi, tio estas bona ideo. = According to me, that is a good idea.

So its exact meaning depends on the sentence.

Because Esperanto uses la before each noun that is definite.

• la planedo = the planet
• la orbito = the orbit

Just as in English, if both nouns are definite, each one normally gets its own article.

Esperanto has only one article, la, and it does not change for gender, number, or case.

No. Esperanto has no indefinite article.

So:

• planedo can mean a planet or just planet, depending on context
• la planedo means the planet

That means Esperanto learners often need to get used to not looking for a word equivalent to English a/an.

Yes, the word order can change more freely than in English, because Esperanto marks grammar clearly with endings and prepositions.

The normal, neutral order is:

• subject + verb + other information

So:

• La planedo moviĝas laŭ la orbito.

But other orders are possible for emphasis or style, such as:

• Laŭ la orbito moviĝas la planedo.

That said, the original version is the most straightforward and natural for a learner.

Yes. Orbito is a clear cognate of English orbit.

The -o ending shows that it is a noun in Esperanto. Many Esperanto words are easy to recognize if you know English or other European languages:

• planedo = planet
• orbito = orbit

This is very common in scientific vocabulary.

In Esperanto, stress is always on the second-to-last syllable.

So:

• plane-do → stress on NE
• mo-vi-ĝas → stress on VI
• or-bi-to → stress on BI

That regular stress pattern is one of the nice predictable features of Esperanto.

The ending -o marks a noun in Esperanto.

So:

• planed-o = planet
• orbit-o = orbit

This is one of the most basic Esperanto rules:

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

Because of this, it is often easy to identify a word’s role just by its ending.

Not with exactly the same feel.

• iri means to go
• moviĝi means to move

A planet in orbit is usually described as moving, so moviĝas is the more natural choice here.

Using iras would sound more like goes, which often suggests directed movement from one place to another. Moviĝas is broader and fits physical motion better in this context.

Not exactly, although English speakers sometimes feel it works a bit like that.

Esperanto does not use -iĝ- as a reflexive marker. Instead, -iĝ- often means that the subject undergoes the action or enters a state.

So:

• Li movas la tablon. = He moves the table.
• La tablo moviĝas. = The table moves.

It is better to think of moviĝi as an intransitive verb formed from movi, not as a reflexive like moves itself.