Learn Hardcore Spanish (Latin America): Se despierta tarde los domingos.

Despertar is normally a transitive verb: despertar a alguien = to wake someone up.
When the person wakes themselves up, Spanish uses the reflexive form despertarse:

Él despierta a su hijo. = He wakes his son up.
Él se despierta. = He wakes up (he wakes himself).

So se is the reflexive pronoun for he / she / usted, and se despierta means he/she wakes up.

Who is the subject here if there’s no word for he or she?

Spanish often drops subject pronouns because the verb ending shows who the subject is.
Despierta is 3rd person singular (he/she/usted). Adding se tells us it’s reflexive but not the gender.

So the subject is understood from context:

It could mean he wakes up, she wakes up, or you (formal) wake up.
To be explicit, you could say Él se despierta…, Ella se despierta…, or Usted se despierta….

What’s the infinitive of despierta, and how is this verb conjugated?

The infinitive here is despertarse (to wake up). It’s a stem‑changing verb (e → ie) in most present‑tense forms:

yo: me despierto
tú: te despiertas
él / ella / usted: se despierta
nosotros / nosotras: nos despertamos (no stem change)
ustedes / ellos / ellas: se despiertan

Non‑reflexive despertar is conjugated the same way but without the reflexive pronouns.

Can I say Él se despierta tarde los domingos? Does adding Él change the meaning?

Yes, Él se despierta tarde los domingos is perfectly correct.
The basic meaning is the same: He wakes up late on Sundays.

The difference is:

Se despierta tarde los domingos. → Subject is only understood from context.
Él se despierta tarde los domingos. → You clearly say he, often used for emphasis or to contrast with someone else:
- Él se despierta tarde los domingos, pero ella se despierta temprano.

Why is it los domingos and not en los domingos for “on Sundays”?

With days of the week, Spanish normally uses the definite article el / los to express “on”:

el domingo = on Sunday (one specific Sunday or “this Sunday”)
los domingos = on Sundays (habitually, every Sunday)

You don’t need en here. En los domingos sounds unnatural in Latin American Spanish for this meaning; los domingos alone expresses the habitual idea “on Sundays”.

What’s the difference between tarde and la tarde? Why is it tarde here?

In this sentence, tarde is an adverb meaning late:

Se despierta tarde. = He/she wakes up late.

La tarde is a noun meaning the afternoon / evening (roughly after lunch until sunset):

Se despierta por la tarde. = He/she wakes up in the afternoon.

So we use bare tarde (no article) because we’re saying late, not the afternoon.

Could I say Se levanta tarde los domingos instead? What’s the difference between despertarse and levantarse?

Yes, Se levanta tarde los domingos is also correct, but it’s slightly different:

despertarse = to wake up (stop sleeping)
levantarse = to get up (get out of bed / stand up)

So:

Se despierta tarde los domingos. = He/she wakes up late.
Se levanta tarde los domingos. = He/she gets out of bed late.

In everyday speech people sometimes blur the distinction, but technically they’re two separate actions.

Could I change the word order and say Los domingos se despierta tarde?

Yes. Los domingos se despierta tarde is grammatically correct and natural.

Se despierta tarde los domingos.
Los domingos se despierta tarde.

Both mean the same thing. The second version puts a bit more emphasis on Los domingos (the time when this habit happens), but in everyday conversation the difference is minimal.

Why don’t we say se despierta a tarde or use any preposition before tarde?

Because tarde here is an adverb, not a noun phrase. Spanish adverbs of manner or time used this way don’t need a preposition:

Llega temprano. = He/she arrives early.
Llega tarde. = He/she arrives late.
Se despierta tarde. = He/she wakes up late.

We would only use a preposition if we were using a noun phrase, such as:

Se despierta por la tarde. = He/she wakes up in the afternoon.

Is se always reflexive with despertar, or can despertar be used without it?

Despertar works both ways:

Reflexive (despertarse) – the person wakes himself/herself up:
- Me despierto tarde. = I wake up late.
- Se despierta tarde. = He/she wakes up late.
Non‑reflexive (despertar a alguien) – one person wakes another:
- Despierto a mi hermano. = I wake my brother up.
- Ella despierta a los niños. = She wakes the kids up.

So se is needed only when the subject and the “person being woken” are the same.