Kiam la suno brilas, longa ombro de la arbo falas sur la straton.

Kiam means when. It introduces a time clause:

• Kiam la suno brilas = When the sun shines
• longa ombro de la arbo falas sur la straton = the main clause

So the whole structure is:

• When X happens, Y happens.

This is very similar to English word order.

Esperanto uses la for a specific or uniquely identifiable thing. La suno is natural because there is only one sun in the situation being described, just like English the sun.

So:

• la suno = the sun
• suno without la would sound less natural here

Esperanto has no indefinite article. There is no separate word for a or an.

So:

• longa ombro can mean a long shadow
• la longa ombro would mean the long shadow

This is a very common feature of Esperanto.

The ending -as marks the present tense in Esperanto.

So:

• brilas = shines / is shining
• falas = falls / is falling

Esperanto present tense is often broader than English. Depending on context, -as can match either:

• simple present: shines
• present progressive: is shining

Adjectives in Esperanto agree with the noun they describe in:

• number: singular or plural
• case: especially the accusative -n

Here, longa describes ombro:

• ombro is singular
• it is not accusative here
• so the adjective is also just singular without -n

That gives:

• longa ombro = a long shadow

If the noun were accusative, the adjective would also take -n:

• Mi vidas longan ombron = I see a long shadow

De often means of, from, or shows a relationship like possession or origin.

Here:

• ombro de la arbo = shadow of the tree / the tree's shadow

So de la arbo tells us which shadow it is.

This is a very normal Esperanto way to express possession or association.

Yes, you could, but the nuance is a little different.

• arba ombro = tree shadow / arboreal shadow, more like an adjectival description
• ombro de la arbo = the shadow of the tree, more directly linked to a particular tree

In this sentence, ombro de la arbo feels very straightforward and natural.

Because la arbo refers to a specific tree, not just any tree.

Compare:

• ombro de arbo = shadow of a tree
• ombro de la arbo = shadow of the tree

So the sentence is talking about a particular tree in the scene.

This is one of the most important points in the sentence.

After a preposition, Esperanto sometimes uses -n to show direction toward a place, not just location.

So:

• sur la strato = on the street
• sur la straton = onto the street

In this sentence, the shadow is described as falling or extending onto the street, so straton takes -n.

The difference is:

• sur la strato = location, already there
• sur la straton = motion or direction toward that surface

Examples:

• La libro estas sur la tablo. = The book is on the table.
• Mi metas la libron sur la tablon. = I put the book onto the table.

In your sentence, falas sur la straton follows the same pattern of movement/direction.

Esperanto, like English, can use fall for things like light, darkness, or shadows.

So ombro falas sur... is a natural, image-based way to say that the shadow stretches or is cast onto a surface.

It is not necessarily about a physical object dropping down. It is a normal figurative use.

Because the sentence begins with a subordinate clause:

• Kiam la suno brilas, ...

Then the main clause follows.

Using a comma here is normal and helps the structure stay clear, much like in English:

• When the sun shines, a long shadow...

Yes, Esperanto word order is fairly flexible because the endings show the grammatical roles.

This sentence uses a very neutral order:

• Kiam la suno brilas, longa ombro de la arbo falas sur la straton.

You could also move parts around for style or emphasis, but this version is clear and standard.

It can often suggest either, depending on context.

Because the sentence is in the present tense and sounds general, many learners would understand it as a general truth or repeated situation:

• Whenever the sun shines, a long shadow of the tree falls on the street.

But Esperanto present tense can also describe a current scene if the context supports that.

So the exact English choice depends on context, not just the verb form.

A quick breakdown:

• Kiam = conjunction/adverb meaning when
• la suno = subject of brilas
• brilas = verb, present tense
• longa ombro = subject of falas
• de la arbo = modifier showing whose shadow
• falas = verb, present tense
• sur la straton = prepositional phrase showing direction/where the shadow falls

So the sentence has:

• a time clause first
• then a main clause with its own subject and verb