For two times in a year, the Earth experiences a solstice and an equinox. What’s even a solstice or an equinox? Are they the same thing? Or is there a difference? And what on Earth causes them even in the first place to begin with. Dear friends, you better grab a globe.
Related media: Equinoxes | National Geographic
What’s A Solstice?
If you think of the difference between a solstice and an equinox as opposites, you’d not be far from right. The word solstice is derived from the Latin words sol which means “sun,” and sistere which means “stationary.” This means that during a solstice, as the sun rises, it appears to be still in the sky at noon for a while before it sets; and as a result, the summer solstice is the longest day of the year. But if you’re at the opposite side of the planet, you’d experience the winter solstice — (you guessed it) the longest night of the year.
The summer solstice happens on June 20 or 21 in the Northern Hemisphere, and on December 21 or 22 in the Southern Hemisphere; whereas the winter solstice happens on December 21 or 22 in the Northern Hemisphere, and on June 20 or 21 in the Southern Hemisphere.
What’s An Equinox?
The word equinox, on the other hand, is also derived from the Latin words aequus, which means “equal,” and nox, which means “night.” You could easily guess where this is going: So on the equinox, the length of day is the same as that of the night. This happens right winter when the season changes, then comes good news — that means spring is here, also known as the vernal equinox. After this season comes summer (that’s when the solstice shows up), until the season changes again, and there comes fall, also known as autumnal equinox.
The vernal equinox happens around March 21 or early April in the Northern Hemisphere, and around September 23 or early October in the Southern Hemisphere; whereas the autumnal equinox happens around September 23 or early October in the Northern Hemisphere, and March 21 or early April in the Southern Hemisphere.
When The Sun Shines Down
Here’s the catch: the Earth isn’t a perfect sphere as depicted in your textbooks. Our planet is actually an oblate spheroid which isn’t perpendicular to it’s axis as it rotates. It’s tilted at an angle of about 23.5 degrees — and always pointed in the same direction in space. Due to this effect, certain parts on Earth get a lot more sunshine than others; and this, in turn, depends on the Earth’s revolution around the sun.
What this means is that, during the winter solstice in the Northern Hemisphere, the Earth points away from the sun as it revolves, thus it gets the least amount of sunshine — but there will be no sunshine at all at the North Pole. Whereas the Southern Hemisphere, on the other side, would get quite a lot of sunshine since the Earth would be pointing towards the sun, making it the summer solstice over there — but in Antarctica, the sun wouldn’t set at all.
In a solstice, the Earth’s axis is tilted away or towards the sun, but in an equinox, the axis of the Earth is tilted directly askew from the sun. During this time, the sun shines directly above the equator, thus the length of day equals that of the night. But this doesn’t last that long, as a new season dawns.
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Written by: Nana Kwadwo, Fri, Aug 30, 2019.