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U.S. & World

What is the Fall Equinox, and is it Really Equal?

By on September 23, 2014

The Fall Equinox is soon approaching here in the Northern Hemisphere, while spring is coming up in the Southern Hemisphere. Many myths have been told about the Equinox, ranging from ability to balance objects, such as eggs or brooms on their ends, to the myth that the day is just as long as the night.

What is the fall equinox

The word equinox comes from the Latin phrase “equal night”. From this phrase a lot of people are misinformed and overgeneralize day and night. Most are led to believe on this day, the daytime is 12 hours long, and the nighttime is 12 hours long, equaling 24 hours. In order to debunk this years old myth, we need to investigate the actual science behind the seasons along with the relationship between the Sun and the Earth.

Seasonal changes are observed by the placement of the Sun in the sky. During the summer we see that the Sun is placed higher and our days last longer, while during the winter we experience a low laying Sun with longer nights and shorter days. What exactly makes these changes occur? Our planet is not rotating around the Sun straight; it is tilted at an angle of about 23.4 degrees. This means as the year goes on one of the Earth’s poles will incline towards the Sun; which is when we experience summer. About six months later the pole will tilt away from the Sun, and the solar energy is at its lowest, and this is when we invite in winter. The points of highest and lowest amounts of solar energy are what we name our solstices. What does this have to do with the equinox though?

Well, what we discussed above sets the precedent for what occurs in between these times of polar opposites. Equinoxes occur when the poles are neither tipped toward nor away from the sun, days and nights are about equal in length compared to how they used to be in winter and summer. Hence the reason we assume that the days and nights are exactly equal, however this assumption may be simple to make, but incorrect.

Equinox Fall

astro.cornell.edu

There are a lot of factors to take into consideration before jumping to the conclusion that these days are completely equal. Everyone has experienced these phenomena’s I’m about to mention; the sunrise and the sunset. What exactly is sunrise and sunset, and why does it affect the uniformity of the day? Sunrise and sunset are the instants at which the edges of the sun, not the center, are barely visible above the horizons. With taking the sunrise and the sunset into account, we notice that the daylight period is actually longer than the nighttime period. Don’t believe it?

Check your local weather listings, Google what time you will experience the sunrise and sunset. When adding these times together, we will see that it is slightly longer than 12 hours. Moreover, don’t overlook twilight. Twilight is not just a sappy teenage vampire romance; twilight is a circumstance that occurs when the Earth’s lower atmosphere is illuminated due to the sun lying directly below the horizon. This causes the surface of the Earth to be not completely dark, but not completely lit.

twilight is the time between dawn and sunrise

Wikipedia.com

Just because we have examined the sunrise and the sunset we don’t actually know why these change the outcome of the day. Have you ever heard of atmospheric refraction? Most haven’t. The definition of atmospheric refraction is the deviation of light or other electromagnetic waves from a straight line as it passes through the atmosphere due to multiple factors, one of them being air density. This definition may be hard to understand at first. A simple breakdown of atmospheric refraction is that our atmosphere plays tricks on us. When the light hits our atmosphere, a reaction occurs which produces mirages, and what we think we see, is not actually happening. This occurrence can cause us to see distant objects rippling or shimmering. It also causes planets, stars, and other astronomical objects to appear higher in the sky than they truly are.

Another supporting piece of evidence to debunk this myth of equality is the position of the sun at the North Pole. When observing the sky from the North Pole, the sun seems to stay a perfect 360-degree circle, looking as if it just skims the edge of the horizon. Now if we hold up with this theory of equal days and nights, then theoretically the sun would completely disappear from view, yet this doesn’t occur at all. As previously explained before, the atmosphere can mess with our eyes. In fact, the atmosphere affects our eyes so greatly that the sun’s perfect 360-degree circle will actually look like an oval when it comes near the horizon. Latitude has a huge role in determining when the hours of the daylight and nighttime will be almost equal in length. When examining the equator, the day and the night are approximately the same length all year round, however the day will also look longer due to atmospheric refraction that was explained above.

All things considered, it may be hard to not believe everything our eyes see, but we need to keep in mind the possibility of optical illusions, and keep our minds open to new possibilities and explanations for these natural phenomena’s.

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