Fall equinox

The September equinox is a specific astronomical moment when the Sun crosses the celestial equator, moving from the Northern Hemisphere to the Southern Hemisphere. In the Northern Hemisphere, this event marks the beginning of astronomical fall (the autumnal equinox), while in the Southern Hemisphere, it marks the start of astronomical spring (the vernal equinox).
Time and Duration of the Equinox
The September equinox occurs at a precise moment in time, not over an entire day. In 2025, the equinox will occur on Monday, September 22, at 18:19 UTC (Coordinated Universal Time). The Sun is not “on” the equator for a duration but crosses it at that single moment. At this instant, the Sun’s rays shine directly on the equator.
Daylight and Its Erosion
The word “equinox” comes from the Latin for “equal night,” suggesting that day and night are of equal length. While this is a common approximation, it’s not perfectly accurate. Due to the way sunrise and sunset are defined (when the upper edge of the Sun’s disk appears on the horizon) and the refraction of sunlight by Earth’s atmosphere, the day is slightly longer than 12 hours everywhere on the planet on the day of the equinox.
After the September equinox, daylight hours begin to erode in the Northern Hemisphere. The rate of this daylight loss is not constant. It is most rapid around the time of the equinox. For locations in the Northern Hemisphere, the amount of daylight lost can be several minutes per day, with the rate of loss increasing as you move farther north.

Daylight loss until September end.

Here is a list of the daylight hours for Merritt, British Columbia from September 17 to September 30, 2025.
| Date | Sunrise | Sunset | Daylight Hours |
|—|—|—|—|
| Sep 17 | 6:42 AM | 7:11 PM | 12h 29m |
| Sep 18 | 6:44 AM | 7:09 PM | 12h 25m |
| Sep 19 | 6:45 AM | 7:06 PM | 12h 21m |
| Sep 20 | 6:47 AM | 7:04 PM | 12h 17m |
| Sep 21 | 6:48 AM | 7:02 PM | 12h 14m |
| Sep 22 | 6:50 AM | 7:00 PM | 12h 10m |
| Sep 23 | 6:51 AM | 6:57 PM | 12h 06m |
| Sep 24 | 6:53 AM | 6:55 PM | 12h 02m |
| Sep 25 | 6:54 AM | 6:53 PM | 11h 58m |
| Sep 26 | 6:56 AM | 6:51 PM | 11h 55m |
| Sep 27 | 6:57 AM | 6:49 PM | 11h 51m |
| Sep 28 | 6:59 AM | 6:46 PM | 11h 47m |
| Sep 29 | 7:00 AM | 6:44 PM | 11h 44m |
| Sep 30 | 7:02 AM | 6:42 PM | 11h 40m |

Source AI