With equinox’s arrival Monday, spring is here — by every measure


Highlights

At 5:38 a.m. Monday, the sun will be directly over the equator, marking the start of “astronomical spring.”

“Meteorological spring” started March 1 for meteorologists who prefer to have fixed beginnings to seasons.

Spring is finally here — by every way of measuring its arrival.

Monday is the vernal equinox, the starting point of spring, as determined by people who base their seasons on the Earth’s position relative to the sun and stars. Here are some answers to frequently asked questions about this rite of spring:

What is the vernal equinox?

At 5:28 a.m. in the Central time zone, the sun is positioned so that it shines directly on the equator, and the northern and southern hemispheres receive exactly the same amount of the sun’s rays. Night and day will be almost equal length. This is an important milestone if you’re into traditional calendars or pagan rituals.

Why is it important?

In many parts of the ancient world, four important dates delineated the seasons: the summer solstice (when spring gives way to summer), the autumnal equinox (when summer gives way to fall), the winter solstice (fall turns to winter) and the vernal equinox (winter to spring).

For two days a year — the equinoxes — the sun is exactly above the equator. And twice a year — the solstices — the sun hits a maximum high or minimum low point in the sky at noon.

These have been important markers on humanity’s journey through time by helping people know such things as when to plant crops or bust out the short pantaloons.

Why only two days when the sun is directly above the equator?

The Earth’s equator is on an axis tilted about 23.5 degrees relative to the sun. That means that, as the Earth rotates around the sun, its northern and southern hemispheres trade places in receiving more light from the sun. At the equinoxes, the axis is neither inclined toward nor away from the sun.

“Equinox” has something to do with Latin, right?

Equinox is derived from the Latin term aequinoctium, which combines equal (aequus) and night (nox).

But day and night won’t be exactly the same length today, will they?

Day and night won’t be exactly the same length. Another designation, equilux, is sometimes used to refer to a day when the amount of light and dark are equal.

So spring starts today? But didn’t spring start awhile back?

Yes, kind of. We’ve had spring-like weather for much of the last few months, with this winter being the warmest on record in Central Texas. So it’s felt like spring almost all winter long. We also had wildflowers blooming — a harbinger of spring — back in February.

But didn’t spring arrive March 1?

That also happened. March 1 was the start of “meteorological spring.” Meteorologists prefer a calendar in which the seasons start on the same days every year. It helps with record keeping, among other reasons. But the Earth, sun and stars don’t quite conform to the Gregorian calendar — thus the vernal equinox doesn’t fall on the same day every year. The vernal equinox follows celestial trends, at the expense of syncing precisely with the western calendar. That’s why the vernal equinox is often said to usher in “astronomical spring.”

CORRECTION: This story has been updated from an earlier version that gave the incorrect time for the equinox. It was at 5:28 a.m. Monday



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