Published on September 18, 2024 at 11:31 a.m.
The first day of astronomical autumn is fast approaching, and it will come earlier than usual – a first in more than 200 years.
The equinox occurs when the Earth’s axis is nearly perpendicular to the Sun, making the length of day and night nearly equal. The exact date of the equinox varies from year to year, ranging from September 21 to September 24.
This year, the autumn equinox will occur on September 22 at 8:43 a.m., marking the official start of the season in the northern hemisphere. The weekend will therefore be marked by this transition to another season. The mercury will be a little cooler than in recent days and will be closer to seasonal norms. Combined with a very present sun, this will soften the official start of astronomical autumn.
This is the first time since 1796 that the equinox has occurred so early. What explains this phenomenon?
Calculations and calculations…
A calendar year ends at 365 days. However, a solar year, which is the time it takes for the Earth to make one complete orbit around the Sun, is on average 365 days, 5 hours, 48 minutes and 46 seconds. Since our way of calculating years is a little shorter, this means that the dates of equinoxes and solstices will change from year to year.
The presence of the leap year is there to compensate and ensure that our calendar follows the solar year – but it’s not perfect. The presence of an extra day every four years overcompensates a bit, since the solar year doesn’t stop at exactly 365 days and 6 hours.
The countless corrections made over the centuries to keep our calendar in line with the solar year are not enough, and the passage of time on Earth is a little out of sync with the Sun’s schedule.
