MIAMI (CBSMiami) – Spring season begins in the Northern Hemisphere this Saturday on March 20th at 5:37 a.m.
This event also marks the Spring Equinox which is also known as the Vernal Equinox or March Equinox. It occurs when the sun crosses over the "celestial equator."
Just imagine yourself floating in deep space and you can see the Earth and the sun at the same time. You first focus on the Earth's equator. Then you imagine a straight line extending outward from the equator into space and toward the sun. This line is the celestial equator.
As your eyes follow the line, going away from Earth, you find the sun on the other end but you notice that the sun is still hanging just south of the line. You then observe the sun positioning itself from south of the line to just north of the line. This is the Spring Equinox occurring right before your very eyes.
Except the sun is not actually moving, instead it is Earth that's moving around the sun. There is one critical feature, however, about the planet that must be taken into account to understand the four seasons and how they happen. That critical feature is the earth's tilt on its axis.
Now if you're asking yourself, "what causes the seasons on our planet?" you may be surprised that it is not due to the change in distance between Earth and the Sun.
Yes, the distance between the two changes as the Earth travels around the Sun on an elliptical orbit. But did you know that Earth is actually closer to the Sun during the winter months than during the summer months?
So then what is actually causing the seasons?
The four seasons occur on Earth because of the planet's tilted axis. Earth's axis tilts at 23.5 degrees and always points in the same direction as the Earth rotates on its axis while orbiting the Sun.
When the Earth is closer to the Sun during late December and early January, the Northern Hemisphere points furthest away from the Sun. Therefore, the Southern Hemisphere receives direct sunlight and longer daylight while the Northern Hemisphere has less sunlight and shorter daylight hours. Resulting in winter for the northern half of the planet and summer for the southern half.
The opposite occurs during June when the Earth is farthest away from the Sun. At this time of the year, the Northern Hemisphere is pointing directly toward the Sun while the Southern Hemisphere is pointing away. In this case, the northern half of the Earth is experiencing summer while it is the winter season for areas south of the equator.
During the equinoxes, both Spring and Fall, the Sun is shining directly on the Earth equally throughout the two hemispheres. This results in almost equal daylight and nighttime hours on the day of the equinox in all of the world. Another fun fact about the equinoxes is that the Sun rises due east and sets due west, this only happens twice a year!
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