Equinox versus equilux: What’s the difference and why does it matter

Why less sunshine starts this week

This week marked an equal amount of daylight and nighttime. Learn more about the equilux.

ATLANTA - This past Saturday marked the autumnal equinox, the point where the sun is exactly over the Earth’s equator.

Contrary to popular belief, that does not mean day and night are both equal in time everywhere. That happens on the equilux.

What is the equinox?

The simple answer to explain the equinox is it's the exact time the sun is positioned directly over the Earth’s equator.

What is the autumnal equinox?

The autumnal equinox, which is the halfway point between the summer and winter solstices, marks the precise moment when the sun appears directly over the Earth's equator.

The means the Earth’s axis is tilted neither toward, nor away from, the sun.

It also marks the halfway point between the summer and winter solstices.

The exact time and date varies from year-to-year.

When is the equilux?

Twice each year holds a perfect balance, 12 hours each, of daylight and nighttime.

The term comes from Latin. "Equi" means equal, and "lux" meaning light.

The time is measured from the official sunrise and sunset.

In Atlanta, this happens a few days before the spring or vernal equinox and a few days after the autumnal equinox. It’s the reverse south of the equator.

What is the equilux?

The misnomer is that there is an equal part of daylight and sunlight on the equinox, but that usually happens a few days before or a few days after, depending the time of the season. It's called the equilux. Why it is import.

The exact date of the equilux depends on the latitude.

The equilux has been slowly creeping down from the northern latitudes since Sept. 25 and will hit close to the equator on Oct. 17.

In Georgia, that date is Sept. 27 this year.

Oddly, there is no equilux at the equator.