The autumnal equinox will occur on September 23, marking the beginning of astronomical autumn in the Northern Hemisphere and spring in the Southern Hemisphere. At this time, the Sun crosses the celestial equator, causing day and night to become nearly equal in length worldwide.

In Pakistan, the September equinox occurs at 5:05am local time on September 23. However, day and night are not exactly 12 hours each because atmospheric refraction and the way sunrise and sunset are measured extend daylight slightly.

For example, Lahore will have about 12 hours and seven minutes of daylight on September 23, while Karachi will have about 12 hours and seven minutes as well. Daylight will continue to shorten across the Northern Hemisphere after the equinox.

Why the equinox matters

The word “equinox” comes from Latin and means “equal night.” The event occurs twice each year, in March and September, when the Sun crosses the equator and seasonal changes take place.

During the September equinox, the Sun rises roughly due east and sets roughly due west. Afterward, Northern Hemisphere locations gradually experience shorter days and longer nights as winter approaches.

The Earth’s tilted axis and its orbit around the Sun cause seasonal changes in daylight throughout the year. The June and December solstices mark the longest and shortest days, while the March and September equinoxes bring the closest balance between daylight and darkness.