even in calendars.. though you might notice it.. the sun is also smiling..
A smile can make people happy, when someone smiles at you.. your quick return would be to smile back at them... its inherent to every person to smile.. only animals doesnt smile...
In calendars, the old times(Astrologers specifically) have depicted the astrological bodies as Human Persons... that is why we have the word "Haring Araw, or the Moon Goddess" they are given the depiction as humans with human traits...
So to give them better attractions to people who uses the calendar.. the early astrologers have depicted them as smiling (as smile can lift ones moods), Just like the Lunar Cycle.. every phases in the Lunar cycle.. is depicted with the moon smiling.. from the New Moon up to the crescent and to the Full Moon, the Moon is depicted as a face that smiles, when the SUn would be up.. the SUn also would be depicted with a Smiley Face..
That is why you get forgotten phrase.. "The Sun has smiled finally", it means that after a tempests or storms/typhoons.. the sun's finally coming up, showing its full bright rays on that region...