Breakdown of A estrela não está nítida a não ser que limpes a lente.
não
not / no
estar
to be (temporary / location)
limpar
to clean
a estrela
the star
Questions & Answers about A estrela não está nítida a não ser que limpes a lente.
Why is limpes used here instead of the normal present tense limpas?
Could I use a menos que in this sentence instead?
Yes, absolutely! a não ser que and a menos que both mean "unless" and are usually interchangeable. Both phrases require the subjunctive, so you could perfectly say: A estrela não está nítida a menos que limpes a lente.
Why do we use está instead of é for "is sharp"?
We use está (from estar, for temporary states) because we are talking about how the star looks right now through the dirty lens. If we used é (from ser, for permanent traits), it would mean the star itself is inherently blurry in space!
Why does the word for "sharp" end in an "a" (nítida)?
Adjectives in Portuguese must agree in gender with the noun they describe. Because it is describing a estrela (the star), which is a feminine noun, the adjective takes the feminine form nítida instead of the masculine nítido.