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Equal Day and Night…

On Wednesday, March 20, 2019, the day and night will be of almost equal duration.

Conventional wisdom suggests that on the equinox everybody on Earth gets to experience a day and night of equal lengths – 12 hours of daylight and 12 hours of night time. In fact, the name equinox is derived from the Latin words aequus, meaning equal, and nox, meaning night.

The March equinox is the vernal (spring) equinox in the Northern Hemisphere and the autumnal (fall) equinox in the Southern Hemisphere.

In the Northern Hemisphere, astronomers and scientists use the March equinox as the start of spring, which ends on the June solstice, when astronomical summer begins.For meteorologists, on the other hand, spring in the Northern Hemisphere begins three weeks before the March equinox on March 1 and ends on May 31.

On the equinoxes the Sun shines directly on the equator and the length of day and night is nearly equal – but not quite. The March equinox marks the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from south to north and vice versa in September.

Although there’s nothing official about it, it’s traditional to say the March or vernal equinox signals the beginning of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. This equinox does provide a hallmark for the sun’s motion in our sky, marking the passage of the sun across the celestial equator, going from south to north. The March 2019 equinox happens on March 20 at 21:58 UTC, which is 4:58 p.m. Central Daylight Time the central U.S.

In the Northern Hemisphere now, we’re enjoying earlier sunrises, later sunsets, softer winds, sprouting plants. Meanwhile, you’ll find the opposite season – later sunrises, earlier sunset, chillier winds, dry and falling leaves – south of the equator.

Here’s another equinox truism. You might hear that the sun rises due east and sets due west at the equinox. True? In fact, this is true. And that’s true no matter where you live on Earth. At the equinoxes, the sun appears overhead at noon as seen from Earth’s equator, as the illustration above shows. This illustration shows the sun’s location on the celestial equator, every hour, on the day of the equinox.

No matter where you are on Earth, you have a due east and due west point on your horizon. That point marks the intersection of your horizon with the celestial equator – the imaginary line above the true equator of the Earth.

That’s why the sun rises due east and sets due west for all of us. The sun is on the celestial equator, and the celestial equator intersects all of our horizons at points due east and due west.

Every year on the Spring Equinox, we hear about how it is the only day of the year when an egg can be perfectly balanced on its end. Many try it and those who fail are told that they didn’t try it at the exact time of the equinox. The truth, however, is that there is nothing magical about the equinox or the time it occurs – you can balance an egg perfectly on its end on any other day.

Don’t believe us? Try it yourself!

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