How would you write it if the article was "a" or "an" or when comparing a singular to a plural??

Question

Would it be "El vestido es tan hermoso como una mariposa?" for the dress is as beautiful as a butterfly?

and is this the same for comparing to multiple objects when the described object is singular: La luz es tan brillante como las estrellas.

Silvia Píriz · Accepted Answer

Hola Natalie a.
Yes, exactly! The structure tan + adjective + como stays the same whether you are comparing singular or plural things. The articles and nouns simply change as needed.
So your examples are correct:
El vestido es tan hermoso como una mariposa. (The dress is as beautiful as a butterfly.)
La luz es tan brillante como las estrellas. (The light is as bright as the stars.)
The adjective agrees only with the noun it describes (hermoso with vestido, brillante with luz), while the second part of the comparison can be singular or plural without affecting the structure.
You could also say things like:
Los coches son tan rápidos como un avión.
El libro es tan interesante como las películas.
So the comparison works perfectly between singular and plural nouns.
Saludos
Silvia