Cuando me siento triste, veo una estrella fugaz.

When I feel sad, I see a shooting star.

Breakdown of Cuando me siento triste, veo una estrella fugaz.

• yo: I
• triste: sad
• cuando: when
• sentirse: to feel

Questions & Answers about Cuando me siento triste, veo una estrella fugaz.

Why is the verb sentirse used reflexively here (me siento triste) instead of just siento triste?

The reflexive form sentirse means to feel (emotion) internally. Using me siento triste indicates that the sadness is something you experience yourself. Saying siento triste without me would literally mean I sense sadness (like detecting it externally), which sounds odd. In Spanish, you always use the reflexive pronoun for personal feelings: me siento feliz, me siento cansado, etc.

Could I use the verb estar instead and say Cuando estoy triste, veo una estrella fugaz?

Yes. Cuando estoy triste... is perfectly correct. Estar triste is actually more colloquial and very common for describing emotional states. Sentirse triste simply emphasizes the act of feeling sadness. Both options convey the same basic idea.

Why is the sentence in the present indicative (me siento, veo) and not the future or the subjunctive?

Here Cuando introduces a habitual or general action—whenever you feel sad, you see a shooting star. For repeated or general facts, Spanish uses the present indicative in both clauses. You’d use the subjunctive only for specific future events:
• Habitual/general: Cuando me siento triste, veo una estrella fugaz.
• Future/specific: Cuando me sienta triste, veré una estrella fugaz (if/when it happens then).