The desire to orient human civilization within the universe is evident in the most ancient structures of the world, including Stonehenge, the Pyramids of Giza and the Pantheon. The baroque architect, priest and polymath, Guarino Guarini (1624–1683), designed seventeen architectural works and wrote ten treatises on a multitude of subjects, including architecture, mathematics and astronomy. Guarini presents three principles in his treatise on architecture, which connects the art of building (edificare) to the sun (orologia, gnomonica) and to solar mechanics (macchinaria). The Church of San Lorenzo in Turin (1668–1687) is an elegant example of these principles created as built form, with a dome resembling the celestial sphere, aligning the church to God and to the cosmos. The vertical alignment of the dome represents the celestial pole, a cosmological center point that is also known as the axis mundi. The interlocked system of stone arcs that comprise the structure of the dome, represents the rings of an ancient model of the celestial sphere known as an armillary that dates as far back as Eratosthenes (276–194 BC). The following dissertation creates an unprecedented connection between Guarini’s knowledge as an architect, mathematician, astronomer and philosopher, to the Church of San Lorenzo. While a previous theory on Guarini by Marcello Fagiolo briefly established the possibility of a system unifying Guarini’s architecture and academic knowledge, I greatly expand this possibility and argue that Guarini is a heliocentric astronomer, not a geocentrist. San Lorenzo was built at the end of the Baroque period and at the beginning of the Enlightenment, representing the bridge between the classical past and the dawn of the age of modern science. By demonstrating that Guarini believed in a sun-centered solar system, I will argue that for Guarini, the light of the sun was architecturally, theologically and cosmologically of the utmost importance.