Juan Ramón Jimenez's aestheticism follows the traditions of the Generación del '27, where he and other poets shifted their style and shared aesthetic traits that are quite evident inAnochecer de Otoño.
The first thing we find is the format: an ephemeral view of an everyday situation. Simple as it is, it is revisited by the poet using a combination of a) imagination vs technique, b) sentiment vs intellect, c) clarity and complexity. These elements make image that Jimenez conveys upon us move, from the basic, towards the magical.
If we were to take away the aesthetic elements in Anochecer de Otoño, we would barely have anything left. Jimenez is basically telling us that he is riding at sundown, when the moon is already out. The street is dark, but he can still see some images. His carriage is loud. People feel sleepy. Through the window of his carriage he can see the silhouettes of males and women in the streets, some keeping each other warm in the cold night. This is what we would get without any aesthetic elements. However, look at how it completely changes with Jimenez's play on words:
Hay luna y no hay alumbrado y la calle es un río blanquiverde, entre orillas frondosas, redondas y negras.
Notice in this verse how he combines imagination and technique: the moon serves as the missing street lights, but its reflection on the nearby river pales in comparison to the river itself, which is described as "blanquiverde, entre orillas frondosas". This gives the river a near-ethereal quality, which shows the aesthetic touch given to an everyday thing.
Then he moves on to sentiment versus intellect, when he talks about the shadows that he sees. To the non-aesthetic eye, a shadow is just a dark space. To an aesthete, is a completely different thing:
Al paso del coche surjen, a la sombra de las sombras, vagas sombras, que no se si son del anochecer or de un recuerdo de Goya que surje en mi memoria.
Here he compares a shadow to the memory of an artist's masterpiece. Quite an imaginative to view a dark spot, but the complexity that he attributes to something otherwise simple is what makes it aesthetic.
Clarity and complexity alternate at all times too:
Silencio. El coche rechina-adormilados caballos, cochero y yo-como si triturara la luna de la calle. Ahora una mujer, una sombra, dice algo que no oigo tras el cristal de la portezuela. Y miro.
Again, he is telling us about a very typical happening in the street: that people feel sleepy, the carriage makes sounds, and that people say stuff that he cannot hear. The added simile como si triturara la luna de la calle, makes for a very clear and strong visual. This completely accentuates the situation towards the complex and imaginative.
The final stamp, that of the men and women in the night, also acquire an element of mystery, and enigma:
Y, contra la verja, bajo un arbol derramado, otra mujer cuyos muscles blanquean de la luna fuera de la falda, abriga con su mantón y sus brazos a un hombre que desaparece escondido en ella.
Hence, we have a powerful description of an everyday happening, with an immense number of added details that transform the narrative altogether from simple to complex, and from natural to almost supernatural. This is what makes this piece a clear sample of aestheticism.