A mi hermana le gusta hacer fotos del cielo cuando hay nubes.

Because gustar works differently from to like in English.

In Spanish, gustar literally works more like to be pleasing to. So:

• A mi hermana le gusta hacer fotos... = Taking photos... is pleasing to my sister = My sister likes taking photos...

So mi hermana is not the subject of gusta. She is the person who receives the feeling, which is why Spanish uses:

• a mi hermana = to my sister
• le = to her

This structure is extremely common with gustar and similar verbs.

They both refer to the same person, but they do different jobs.

• le is the indirect object pronoun: to her
• a mi hermana clarifies who that le refers to

So in:

• A mi hermana le gusta...

both parts mean something like to my sister, but Spanish normally keeps the pronoun le even when the full noun is also present.

This is called clitic doubling, and it is very natural in Spanish.

You can think of it like:

• To my sister, she likes... — not natural in English, but normal in Spanish structure

Without a mi hermana, the sentence would still be grammatical:

• Le gusta hacer fotos del cielo cuando hay nubes.

But then we only know that someone likes it, depending on context.

Because the thing being liked here is hacer fotos del cielo cuando hay nubes, which is an infinitive phrase.

When what follows gustar is an infinitive, Spanish uses singular:

• Me gusta leer.
• Nos gusta viajar.
• Le gusta hacer fotos.

So here, the whole action hacer fotos del cielo cuando hay nubes is treated as one thing, which is why it is gusta.

You would use gustan if the subject were a plural noun:

• Le gustan las fotos. = She likes the photos.
• Le gustan las nubes. = She likes clouds.

After gustar, Spanish often uses an infinitive to talk about liking an activity.

So:

• le gusta hacer fotos = she likes taking photos

This is very similar to English likes taking photos or likes to take photos.

Other examples:

• Me gusta cocinar. = I like cooking.
• Te gusta nadar. = You like swimming.
• Nos gusta salir. = We like going out.

So hacer fotos is the activity that she likes.

Yes, hacer usually means to do or to make, but in Spanish it is also used in the expression:

• hacer fotos = to take photos

In Spain, hacer fotos is very common and natural.

You may also hear:

• sacar fotos in some regions
• tomar fotos more often in much of Latin America

So if you are learning Spanish from Spain, hacer fotos is a very good choice.

Fotos is simply the shorter, very common version of fotografías.

• foto = photo
• fotografía = photograph

Both are correct, but foto(s) is much more common in everyday speech.

So:

• hacer fotos sounds natural and normal in conversation.

Del is the contraction of:

• de + el = del

So:

• del cielo = of the sky / from the sky

In this sentence, fotos del cielo means photos of the sky.

Spanish often uses de where English uses of:

• una foto del mar = a photo of the sea
• una foto del cielo = a photo of the sky

You cannot say de el cielo here; it must contract to del cielo.

Because hay means there are, and that is the idea Spanish wants here:

• cuando hay nubes = when there are clouds = more naturally in English, when it’s cloudy / when there are clouds

Están nubes is not correct, because nubes are not describing the location or state of something with estar here.

Son nubes would mean they are clouds, which is a different idea.

So hay is the right choice because it introduces the existence of clouds.

After hay, Spanish usually does not use the definite article unless you mean specific clouds already known in the context.

So:

• hay nubes = there are clouds / it is cloudy
• hay las nubes would sound wrong in this sentence

If you said las nubes, you would usually be talking about specific clouds:

• Mira las nubes = Look at the clouds

But here the meaning is general, so nubes without an article is correct.

It is placed first to show clearly who the sentence is about.

Spanish word order is flexible, and starting with A mi hermana helps frame the sentence:

• A mi hermana le gusta... = As for my sister, she likes...

You could also say:

• Le gusta hacer fotos del cielo cuando hay nubes a mi hermana

but that sounds less natural in most normal contexts.

So the original order is the most common and clear.

It describes the action hacer fotos del cielo.

The idea is:

• She likes taking photos of the sky when there are clouds

So cuando hay nubes gives the time or condition under which she likes taking the photos.

It does not mean that the sky when there are clouds is some separate noun phrase. It is better understood as:

• [le gusta] [hacer fotos del cielo] [cuando hay nubes]

Yes, but the most natural choice depends on the variety of Spanish.

For Spanish from Spain:

• hacer fotos is very natural and common

Also possible in some contexts:

• sacar fotos

More common in many parts of Latin America:

• tomar fotos

So if your target is Spanish from Spain, the original sentence sounds very appropriate.

By itself, mi hermana means my sister.

The idea to my sister comes from the full phrase:

• a mi hermana = to my sister

That a is important because it marks the indirect object with gustar.

So:

• mi hermana = my sister
• a mi hermana = to my sister

In this sentence, the full phrase a mi hermana is needed because of how gustar works.