Today, September 23, marks the 2025 spring equinox in Australia and the Southern Hemisphere, meaning days will be longer than nights for the next six months.

What is the spring equinox?

Earth’s tilted axis means its orientation relative to the sun changes throughout the year. For half the year, the Southern Hemisphere is oriented more towards the sun and for the other half of the year, it is oriented more away the sun. The equinox marks the day of transition between these two phases.

There are two equinoxes each year, one in September and the other in March. The Southern Hemisphere’s spring equinox (Northern Hemisphere’s autumn/fall equinox) occurs in late September each year, marking the moment the sun appears to pass over the equator as the Southern Hemisphere becomes more oriented towards from the Sun.

The sun’s position above earth’s equator on the date of the equinox makes the solar terminator (line between day and night) run perpendicular to earth’s equator.

Image: Sunrise over Australia on September 23, 2025, showing the solar terminator running perpendicular to earth’s equator. Source: RAMMB / CIRA

Days longer than nights

There are roughly equal amounts of daylight and darkness across Earth on the date of the equinox. However, day and night are not exactly equal in length on the equinox.

The sun’s large size, the way we define daylength and the ability of earth’s atmosphere to bend light mean that there is slightly more daylight than darkness on the date of the equinox. For many areas on earth, day and night are closer in length a few days before the date of the spring equinox, on a date referred to as the equilux.

In Melbourne for example, there will be about 12 hours and 10 minutes between sunrise and sunset on the date of the spring equinox. Day and night were closest in length on September 19-20 in Melbourne this year.

Image: Sunrise and sunset times for Melbourne in the Weatherzone app on the date of the 2025 spring equinox.

Days will become longer than nights across Australia for the next three months until the longest day of the year occurs on the summer solstice in late December. Nights will remain shorter than days across the country until the next equilux in March next year.