Astronomical autumn arrives in Spain in the early hours of Wednesday, September 23, marking the official end of summer and the beginning of a season when daylight starts disappearing noticeably faster.

According to Spain's National Astronomical Observatory, astronomical autumn begins at 2:05am Spanish mainland time on September 23, 2026. The season will last approximately 89 days and 21 hours, ending with the arrival of winter on December 21.

For Ibiza and the rest of the Balearic Islands, the seasonal change takes place at the same local time as mainland Spain.

Daylight Starts Disappearing Quickly

One of the most noticeable changes at the beginning of autumn is not necessarily the temperature, but the amount of daylight.

The National Astronomical Observatory says early autumn is the time of year when day length shortens most rapidly at Spanish mainland latitudes.

Around the start of the season, the Sun rises more than a minute later each morning and sets more than a minute earlier each evening.

Combined, that means Spain loses almost three minutes of daylight each day.

Over a week, that can add up to roughly 20 minutes less daylight, although the exact change varies according to location.

The Autumn Equinox

The start of astronomical autumn is determined by the autumnal equinox.

This occurs when the centre of the Sun crosses the celestial equator in its apparent movement towards the south.

At that point, day and night are approximately the same length, although they are not exactly equal because factors including atmospheric refraction affect the observed times of sunrise and sunset.

After the equinox, nights gradually become longer and daylight continues to decrease across the Northern Hemisphere until the winter solstice.

Summer Ends on the Calendar, But Heat Can Continue

The arrival of astronomical autumn does not mean Spain will suddenly become cooler.

Temperatures can remain firmly in summer territory well after the astronomical change of season, particularly in southern and Mediterranean areas.

That is especially relevant this year following an exceptionally hot summer across Spain.

AEMET says summer 2026 was the hottest in its official series, which runs from 1961 onwards. Its reconstructed climate record extending back to 1869 also indicates that 2026 was the hottest summer in at least the past 157 years.

The Balearic Islands were classified as having an extremely hot summer.

A Warm Autumn Is Currently Expected

The latest seasonal outlook from AEMET also suggests that the warm weather may continue.

For September, October and November, AEMET currently gives a 60-70% probability that temperatures across Spain will be above the 1991-2020 average.

The agency says the warm signal is particularly strong across areas including eastern Spain and the Balearic Islands.

That means Ibiza is currently expected to experience a warmer-than-normal autumn overall, although seasonal forecasts do not predict the temperature of individual days.

Rainfall Could Also Be Higher in the Balearics

The temperature outlook is not the only interesting part of the forecast.

AEMET currently gives a greater probability of above-normal rainfall during September-November across the Mediterranean side of Spain and the Balearic Islands.

For Ibiza, that could mean the autumn transition brings more unsettled weather at times, even while temperatures remain above average over the season as a whole.

A seasonal rainfall forecast should not, however, be interpreted as a prediction of a particular storm or amount of rain on a specific date.

Ibiza's Days Will Now Get Shorter

For people in Ibiza, the change will become increasingly noticeable during the coming weeks.

Sunsets will continue arriving earlier and sunrises later as the island moves away from the long days of summer.

The pace of change is greatest around the equinox and gradually slows as autumn progresses towards December.

The effect is particularly noticeable after several months of long Mediterranean evenings, when outdoor dining, beach visits and late sunsets have become part of daily life.

The Clocks Will Change in October

There is another seasonal change still ahead.

Spain will continue using its existing daylight-saving arrangements in 2026, with the clocks scheduled to move back one hour on Sunday, October 25.

On the Spanish mainland and in the Balearic Islands, clocks will move from 3:00am back to 2:00am.

The Canary Islands will make the corresponding change from 2:00am to 1:00am.

Autumn Brings New Night-Sky Events

The new season also brings a changing night sky.

The National Astronomical Observatory says Mercury and Venus will be visible after sunset around the beginning of autumn, with Saturn appearing a few days later.

Later in the season, several meteor showers will provide opportunities for stargazing, including the Draconids in October, the Orionids in October, the Leonids in November and the Geminids in December.

The autumn full moons will occur on September 26, October 26 and November 24.

A Different Kind of Seasonal Change

The arrival of autumn is therefore about more than a change in the calendar.

For Ibiza and the rest of Spain, the next few months will bring steadily shorter days and longer nights, even as temperatures may remain higher than traditional autumn expectations.

This year's transition is particularly notable after Spain's exceptionally hot summer and with AEMET currently expecting above-normal temperatures across the country during the autumn season.

For now, the biggest immediate sign that summer is moving on may not be colder weather.

It will be the evenings getting shorter, almost three minutes of daylight at a time.