That's the literal translation of the word Equinox. And there are two of them each year.
One in the spring and one in the fall, when the sun is overhead the equator and the length of daylight and darkness are equal.
The extreme happens at the time of the Solstices.
In winter the Solstice is the longest night.
In summer the solstice is the longest day.
The farther north you go, the more extreme this difference becomes.
Our native Northern European ancestors divided the circle of the year into two parts.
They were either going into the dark or going into the light.
Winter Solstice at about December 21 is the longest night and from that time forward the days begin to lengthen.
Going into the light.
Summer solstice at about June 21 is the longest day and from that time forward the nights begin to lengthen.
Going into the dark.
So to celebrate Spring Equinox is to mark the half way point between Winter Solstice and Summer Solstice.
Once we reach Summer Solstice, the Great Wheel will turn and we will begin, again, to go into the dark.
This eternal dance is beautifully expressed in the shape and the meaning of the Dagaz rune.