Astronomical autumn 2026 begins in Spain on Wednesday 23 September at 02:05 on the Iberian Peninsula and the Balearic Islands. In the Canary Islands the season begins at 01:05. The Observatorio Astronómico Nacional at the Instituto Geográfico Nacional gives these times as the official calculation of the start of autumn.
The cause is the equinox: At this precise moment, the centre of the Sun’s disc crosses the celestial equator southwards along its apparent path. In the northern part of the Earth, this marks the start of autumn; day and night are almost equal in length around this date. In Spain, the changeover therefore takes place at night, before the sun rises in many places.
The date varies from year to year between 21 and 24 September. This is because the calendar has a fixed length, while the Earth’s actual orbital and rotational dynamics do not align exactly with it. The start of autumn is therefore not an arbitrary calendar date, but an astronomically defined moment, listed by the Observatorio Astronómico Nacional in its annual calendar and ephemerides.
The effects of the equinox should be clearly distinguished from weather and climate. After the start of autumn, days in Spain gradually become shorter and dusk sets in earlier. This has practical implications for energy use, road safety and urban lighting plans. In agriculture and ecology, vegetation cycles and the migration periods of many bird species shift. Weather transitions, however, vary by region; autumn-like weather may arrive earlier or later than expected.
The Instituto Geográfico Nacional, through its Observatorio Astronómico Nacional, is responsible for official time information in Spain. It publishes the precise times of equinoxes and solstices and provides supplementary astronomical data. Statements about typical weather or seasonal averages, by contrast, are based on climate assessments and not on a single astronomical event.
For the public, this sets the definitive timestamp for the seasonal transition in Spain: 23 September 2026, 02:05 on the Iberian Peninsula and the Balearic Islands, and 01:05 in the Canary Islands. Autumn begins and summer ends — astronomically defined with precision by the crossing of the celestial equator.
Editor: Andreas M. Brucker (Article created with AI assistance).