Earth will mark the beginning of autumn in the Northern Hemisphere when it passes through the point in its orbit from which the center of the Sun crosses the celestial equator in its apparent southward movement. This phenomenon determines the astronomical start of the new season.
On that day, the lengths of day and night are practically equal, a circumstance also known as the autumnal equinox. While the Northern Hemisphere welcomes autumn, spring begins in the Southern Hemisphere.
The National Astronomical Observatory notes in a report on autumn, cited by Servimedia, that the equinox of this season can occur on as many as four different dates and begin between September 21 and 24. Throughout this century, autumn begins on September 22 or 23, with its earliest start in 2096 and its latest in 2003.
These variations from one year to another are due to the way the sequence of calendar years, including leap years and non-leap years, fits with the length of each of Earth's orbits around the Sun.
The beginning of autumn is also the time of year when the length of the day decreases most rapidly. At the latitudes of the Iberian Peninsula, the Sun rises more than a minute later each morning than it did the previous day and sets more than a minute earlier in the afternoon. Thus, at the start of the season, the time the Sun remains above the horizon is reduced by almost three minutes each day.
TIME CHANGE
The usual time change will take place on the last Sunday of October, the 25th. At 3 a.m., clocks will have to be set back to 2 a.m., and to one hour earlier in the Canary Islands, meaning that day will officially have an extra hour.
Although the Spanish government, the European Parliament and the European Commission have spoken in favor of eliminating time changes in the future, no final decision has yet been made. Therefore, the traditional time change that takes place on the last Sunday of October will remain in effect in 2026.
The first full moon of autumn will appear on September 26. The following ones will occur 29 or 30 days later, specifically on October 26 and November 24.
As for the planets, Mercury and Venus will be visible after sunset at the beginning of autumn. Saturn will appear a few days after the start of the season. Venus will be observable until mid-October and Mercury until the end of that month.
At dawn, meanwhile, Mars and Jupiter will be visible. Venus will make its appearance at the end of October, while Mercury can be observed from mid-November to mid-December.
STARS AND CONSTELLATIONS
Among the stars and constellations that can be observed at night during autumn, the Summer Triangle will stand out, formed by Deneb in Cygnus, Vega in Lyra and Altair in Aquila. It will remain visible during the first part of the season, although it will gradually appear lower above the western horizon.
As the months go by, the constellations Pegasus, Andromeda and Perseus will emerge in the east. At the end of the season, Taurus and Orion will appear, reaching their greatest splendor during winter nights.
Other astronomical phenomena of interest during autumn will include the Draconid meteor shower, expected to peak around October 8; the Orionids, peaking around October 21; the Leonids, around November 17; and the Geminids, around December 14.
