Tramontare vs. calare
While both tramontare and calare can be translated as to set or to go down when referring to the sun, they are not always interchangeable. Tramontare is the more specific and poetic term for this event, while calare has a much broader meaning of to lower or to decrease.
Tramontare
B1This is the primary and most appropriate verb for the sun or moon setting. It specifically describes the celestial body disappearing below the horizon. The word itself comes from tra i monti (beyond the mountains), giving it a more evocative and definitive feel. Figuratively, tramontare is very common and means to fade, to decline, to end, or to go out of fashion, often used for abstract concepts like eras, fame, or hope.
Andiamo in spiaggia a guardare il sole che tramonta.
(Let's go to the beach to watch the sun set.)
Amo il colore del cielo quando il sole tramonta.
(I love the color of the sky when the sun goes down.)
L'impero romano è tramontato secoli fa.
(The Roman Empire declined centuries ago.)
La sua fama è tramontata velocemente dopo il film.
(His fame faded quickly after the movie.)
È uno stile che non tramonta mai.
(It's a style that never goes out of fashion.)
Calare
A2This verb's core meaning is to lower, to drop, or to decrease. When used for the sun, calare describes the physical action of it moving downwards in the sky. It is a more generic and less poetic alternative to tramontare. Its versatility is its key feature, as it can be used for many other things: lowering an object, prices decreasing, or darkness and silence falling. The expression al calar del sole (at sundown) is very common.
Dobbiamo tornare prima che cali il sole.
(We have to be back before the sun goes down.)
Quando cala la notte, la città si illumina.
(When night falls, the city lights up.)
L'attore attende che cali il sipario per ringraziare il pubblico.
(The actor waits for the curtain to fall to thank the audience.)
I prezzi delle case stanno iniziando a calare.
(House prices are starting to drop.)
Per favore, cala le tapparelle, c'è troppa luce.
(Please, lower the blinds, there is too much light.)
Appena l'acqua bolle, puoi calare la pasta.
(As soon as the water boils, you can drop the pasta in.)
Summary
In essence, use tramontare as the specific, standard, and more poetic verb for the sun setting. It is also the correct choice for the figurative decline of abstract things like fame, empires, or styles. Use calare as a more general verb for to lower or to decrease. While it can describe the sun's descent in a more physical sense, its main strength is its use for a wide range of other subjects, such as prices, curtains, darkness, and objects being lowered.