Telling the autumn equinox

In order to remember the 800 years of the foundation of the basilica of Santa Maria Novella and the 700th anniversary of the death of Dante Alighieri, we have thought of a particular event for the day of the autumn equinox, 22 September 2021 at 11.45 am, with 3 interventions of about 20-30 minutes each.

It could follow the observation of the passage of the sun on the meridian line at 13h 07m 38s.

The vernal equinox is intimately connected to the basilica and to Dante for various reasons:

• the basilica was founded, overturning the 90 ° orientation, on the pre-existing Romanesque church, oriented towards the dawn of the equinox;
• Masaccio creates the fresco of the Trinity in the position in which it can be illuminated on the day of the equinox;
• Egnazio Danti creates astronomical instruments to precisely measure the vernal equinox and calculate the length of the year;
• Dante Alighieri sets up his journey of the Divine Comedy in the days around the equinox.

Between 1572 and 1575, the cosmographer Egnazio Danti (1536-1586) installed three astronomical instruments on the facade of Santa Maria Novella: a large dial with sundials, an equinoctial armilla, and a gnomon hole for a darkroom sundial . These instruments had the purpose of accurately identifying the moment of the autumn equinox and therefore favoring new astronomical calculations intended for the Julian calendar reform project which should have definitively re-established the liturgically exact date of Easter and the related movable feasts.

Recent studies and surveys have highlighted the relationship that links Masaccio's Trinity with the sun and the millennial symbolism assigned to light as the very essence of God and to the day of the autumn equinox. It is no coincidence that the equinox is closely linked to the calculation of Easter and therefore to the resurrection of Christ. In fact, on the occasion of the autumn equinox, the sun coming from the second eastern eye of the main nave perfectly illuminates the figure of Christ who will have to rise again.

Dante Alighieri also structures his journey into the three otherworldly worlds, reported in the Divine Comedy, precisely in the days around the autumn equinox and describes the depth of the symbolic meaning of the equinoctial cross in his verses. In this regard, the similarity with the cross-shaped shadow visible on the facade of the basilica, generated by the armilla on the day of the equinox, is very striking.

- Speakers

P. Manuel Russo O.P., Opera for Santa Maria Novella: Historical and symbolic aspects of Masaccio's Trinity

Riccardo Pratesi, Museo Galileo: “The Sun went up with those stars”. Dante's equinoctial journey

Simone Bartolini, Military Geographical Institute: Astronomical time and human time: The equinox and the calendar. Masaccio's Trinity and equinoctial light

Guided observation of the passage of the Sun on the meridian line

Solar noon: 13h, 07m and 38s