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Let's observe the sunspots on the sun.
Literal
Sun [genitive-の] sunspots [object-を] let's-observe.
A short, instructional invitation. 黒点を観察する ('to observe sunspots') pairs the formal verb 観察する (かんさつする, 'to observe / to study') with the science term 黒点. ~しよう is the volitional of する — 'let's do.' The sentence reads like a science-class activity prompt or educational guide heading. Simple and direct.