Equinoxal Crossover of the Spring Full Moon

April 22, 2024


Photographer: Cristóbal Sánchez 
Summary Author: Cristóbal Sánchez

These captivating images, taken on September 28, 2023, unveil a rare phenomenon atop the Andean mountain, Nevado de Juncal, standing at 19,573 ft (5,966 m). The intriguing crossover reveals a unique synchronization of the Sun and the Moon rising over the same mountain peak. This occurs only every 19 years, precisely a week after the spring equinox (Southern Hemisphere). Such an alignment coincides with the emergence of the spring full Moon in the Southern Hemisphere, allowing both celestial bodies to grace opposite horizons, casting an intense amber glow upon the snow-clad mountain during moonrise (bottom photo).

This cyclical event holds profound significance for archaeoastronomy, shedding light on the Incan worldview and their strategic observational infrastructure. The Andean Mountains serve as exceptional guides, aiding in the determination of lunar and solar standstills.

The mesmerizing display epitomizes celestial harmony, governed by the Metonic Cycle, whose lunar phases repeat the same dates after 19 years -- complementing the Saros Cycle's predictions of solar eclipses every 18.6 years. Additionally, the elliptical coincidence aligns with the lunar nodal precession, defining the time for the ascending node's 360 degree rotation relative to the vernal equinox. This influences the duration of a draconic month, shorter than the sidereal month. After one nodal precession period, draconic months exceed sidereal months by exactly one day. This period spans about 6,793 days or 18.6 years.

Beyond its archaeological significance, the novelty of this spectacle lies in the precise alignment of the springtime full Moon and the Sun atop the same mountain peak. Capturing this precise alignment is unprecedented. This rare event, documented without relocating the camera tripod from its position at Las Antenas de Caleu in central Chile, signifies an astro-landscape synchrony that will not grace this exact location again until the year 2460, spanning 23 Metonic Cycles

Photo Details: Sun Data - Sony ZE10 camera; Askar 200 lens; f/22; ISO 100; 1/4000 second exposure; 07:41 (UTC-3). Moon Data - Sony ZE10 camera; Askar 200 lens; f 5.6; ISO 100; 1/100 second ecposure; 19:23 (UTC-3)

Las Antenas de Caleu, Chile Coordinates: -33.046111, -71.000778

Related Links:
Lunar Standstill and Saros Cycle
Cristobal’s Website