Sky – el cielo
(Pronounced see-eh-loh)
To remember that sky is pronounced see-eh-loh (cielo) in Spanish, use the following mnemonic:
In the sky, they could see a low (cielo) aeroplane disappearing over the horizon.

Cielo is masculine, so it’s el cielo. Imagine a herd of elephants flying through the sky:

Examples of cielo (sky) in a sentence
El cielo está muy azul hoy.
(The sky is very blue today.)
Las estrellas brillan en el cielo por la noche.
(The stars shine in the sky at night.)
Los pájaros vuelan alto en el cielo.
(The birds fly high in the sky.)