CHAPTER III--Unveiling the Open and Hidden Functions of the Mysterious North Dome of Isfahan: How Omar Khayyam Designed, for His Commissioned Projects of Solar Calendar Reform and Building Its Astronomical Observatory, Iran's Most Beautiful Dual-Use Structure for the Annual Celebration of Nowrooz.

This chapter investigates the mysterious function of the nearly one-thousand-year-old “North Dome” in the northern wing of Iran’s Masjed-e Jameʿ (Friday or Ancient Mosque) of Isfahan, widely regarded as one of Iran’s most beautiful structures but whose purpose has long been debated. Drawing on historical context, architectural studies, and especially Omar Khayyam’s Nowrooznameh—a previously untranslated text emphasizing the importance of solar calendar reform and Nowrooz (Persian New Year) celebrations—the author argues that the North Dome was a dual-use structure designed by Khayyam. It served both as part of an astronomical observatory for solar calendar reform commissioned by Soltan Malekshah’s court (1072–1092 AD) and as a dedicated site for the annual Nowrooz celebration, embodying Khayyam’s philosophical, theological, and poetic worldview, including symbolic elements reflecting his Robaiyat poetry. The chapter critically reviews prior scholarship, highlighting the dome’s precise architectural proportions linked to the Golden Ratio and a unique “Khayyami triangle” derived from Khayyam’s treatise on dividing a circle quadrant, and interprets the dome’s intricate pentagonal ceiling pattern as a lasting, multi-layered metaphor incorporating astronomical symbolism (notably the orbit of Venus), spiritual themes, and the concept of “Khargāh” (a grand tent), a metaphor resonant with Khayyam’s own name and legacy. The author contends that the North Dome’s attribution to Taj al-Molk, a junior court official and rival of vizier Nezam al-Molk, obscured Khayyam’s central role in its design and that recognizing Khayyam as its architect restores the historical and cultural significance of this unique monument as a masterpiece of Islamic art, science, and poetry intimately tied to Iran’s solar calendar reform and Nowrooz tradition.