Today is the Spring Equilux. What is the difference between the equilux and the equinox?

On the equinox the length of day and night are only nearly equal.

The equilux is when day and night are equal and occurs a few days before the spring equinox, and a few days after the autumn equinox.

This is because the sun appears as a disk in the sky, and the top half rises above the horizon before the centre.

As well as this, sunlight is refracted by the Earth's atmosphere.

The sun therefore, appears to rise before its centre is at the horizon giving more daylight than you might expect (12 hours 10 minutes on the equinox).