Shabeh Yalda (Persian: Night of Yalda/Yalda Night), or winter solstice, marks the first day of winter (December 21 in the Northern Hemisphere and June 20 in Southern Hemisphere.)And as the longest and darkest night of the winter, Shabeh Yalda is a time of gathering and celebration for many Iranians: Big bowls of mixed nuts (aa-jeel) where shiny, salted pistachios, sunflower seeds, and almonds smile at guests; pink, sweet watermelon (sometimes carved and shaped into pretty objects), a basket of fruits–including plenty of pomegranate–and several plates of Persian pastry are just a few common items decorating the table on Shabeh Yalda at any participating Iranian home.

Scientifically, the winter solstice occurs when Earth’s axial tilt is furthest away from the sun, making days shortest and nights longest, for places with the highest latitudes.

The significance of winter solstice is more evident in cultures where the solar calendar is used and the seasons are marked based on the movements of the sun. Therefore, making the beginning of some seasons a time for celebration and gathering. For example, just as celebrating the first day of spring, Norooz, the Persian new year is important, celebrating the first day of winter also holds special magnitude in Iranian culture.

The tradition of celebrating Yalda dates back to the Mithraism religion and it’s rituals of honoring good over evil. Originally, it was believed that last night of the month Azar (November 22-December 21) when winter solstice occurs, is a dark time in which forces of evil are at their highest power. The next day and the first day of the month Dey (Dec 22-Jan 19), however, marks the victory of sun–symbol of good–over evil since, days become longer and nights grow shorter; leading up to spring and the Persian New Year, Norooz. On the other hand, the word Yalda means birth which was used by Mithraists to refer to the the birth of Mithra, the Sun God. Centuries later, when Zoroastrianism was practiced in Iran and some principals of Mithraism were adopted by Iranians, Mithra became the equivalent of Ahura Mazda or the God of Goodness. Thus, making the birth of Mithra, a happy and celebratory occasion.

Today, Shabeh Yalda is just a symbolic fete of togetherness and joy. In the 11th century, Iran experienced changes and Islam became the official religion–followed by the Arab conquest during Sassanid dynasty–but some Zoroastrian rituals were kept, like celebrating Yalda. It remained popular but was no longer considered a religious holiday; labeled solely a social and gathering occurrence.

The most enchanting part of Yalda Night parties, is the reading of Persian poetry and Moshaa-ereh or debate poetry. In Moshaaereh, participants must recite a line of poetry beginning with the last letter of the previous poem read. This part of the night is often moderated by an elder or anyone who has knowledge of literature. Hafiz, the great 14th century poet whose divine Divan can be found in almost any Iranian household, is often used to sound off these oratory deliberations.

Poetry plays a fixed, cherished role in Iranian values and philosophical matters: Questions about life and human nature are often expressed in Persian poetry–hence, Shabeh Yalda is spent reflecting on the transcending messages in these timeless works of art.

Of course, let’s not forget that the more modern versions of recognizing Yalda exist too: Lavish parties where food is served and guests dance together all night are certainly a normal invitation to receive (in or out of Tehran) not to mention all the club bashes across the globe, where next generation Iranian 20-somethings help keep the tradition alive in their own way. (Other Persian-speaking peoples such as Iranian Jews, Tajikis and Afghans also honor Shabeh Yalda: The fact that this practice has remained active and holds an important place in Iranian lifestyle, reflects the depth of richness in Persian beliefs and the great amount of attention paid to enjoying life, spending time together, being hospitable, and most importantly being cheerful.)

I remember feeling eager and overjoyed every year to experience this usually-chilly, long night filled with eruptions of excitement and laughter, as a young girl in Iran. Besides my address, things haven’t changed much for me since.

As renowned Iranian poet Sa’adi mentions in his Bustan, ‘the true morning shall not until the Yalda Night has gone.”

This December 20th, don’t forget to wish your friends and family a shaad (Persian: happy) Shabeh Yalda!