What you need to know about the seasons

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PORTLAND, Ore. (KOIN) – Have you ever had dreams of seeing the earth from outer space? Thursday, we will get a small chance to imagine that as we take a look outside the boundaries of our everyday view. We will also watch a video about the Spring Equinox, which will help visually show and explain how the vernal equinox works.

Earth Orbit Generic Example – Courtesy NWS

Why does the earth have seasons? The earth revolves around the sun in an elliptical path. You can see that in the photo to the left.

But what is unique about our setup is the earth axis is tilted at 23.5 degrees. One thing to remember is the earth’s axis always points to the same area in space.

Now it takes the earth, you’ve guessed it, 365 days to completely travel around the sun (a little longer for a leap year). As the earth spins on its own axis, it completes one spin in 24 hours (one day). It is the tilt and the path that determines the seasons of the year.

Those seasons: December 21-22 Winter Solstice , March 20-21 Vernal Equinox, June 20-22 Summer Solstice, September 22-23 Autumnal Equinox

Solstice: The summer solstice occurs at the moment the earth’s tilt toward from the sun is at a maximum. Therefore, on the day of the summer solstice, the sun appears at its highest elevation with a noontime position that changes very little for several days before and after the summer solstice.  The summer solstice occurs when the sun is directly over the Tropic of Cancer, which is located at 23.5° latitude North. For every place north of the Tropic of Cancer, the sun is at its highest point in the sky and this is the longest day of the year.

The winter solstice marks the shortest day and longest night of the year. In the Northern Hemisphere, it occurs when the sun is directly over the Tropic of Capricorn, which is located at 23.5° south of the equator.

Equinox: There are only two times of the year when the Earth’s axis is tilted neither toward nor away from the sun, resulting in a “nearly” equal amount of daylight and darkness at all latitudes. These events are referred to as Equinoxes. The word equinox is derived from two Latin words – aequus (equal) and nox (night). At the equator, the sun is directly overhead at noon on these two equinoxes.  The “nearly” equal hours of day and night is due to refraction of sunlight or bending of the light’s rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon.

You can now watch a video of the spring equinox below –

I’ll pass it on to Chief Meteorologist Natasha Stenbock to fill you in on why Spring is a bit more special this year.

Thank you, Joseph. So here is exciting news Spring is sprouting one day early this year: Thursday March 19 at 8:49 p.m. PDT. 

Chief Meteorologist Natasha Stenbock

According to the Farmers Almanac, “For much of the last century, the spring equinox has occurred on March 20 or 21. However, this year the equinox happens on the 19th in all U.S. time zones, making it the earliest spring we’ll have seen in our lives (so far). The last time spring arrived this early was in 1896—a whopping 124 years ago!”

So why the sudden rush, Spring? Blame it on the leap year. Get ready, there’s a lot of numbers involved to explain this calendar dilemma.

In reality, March 16 is when day and night are both closest to 12 hours from Portland, Oregon, with sunrise at 7:20 a.m. and sunset at 7:18 p.m.  At the 45th latitude North, the time it takes for the sun to fully rise and set, which is several minutes, is added to the day and subtracted from the night, and therefore the equinox day lasts a little longer than 12 hours. Another reason why the day is longer than 12 hours on an equinox is that the Earth’s atmosphere refracts sunlight.  After March 17, daylight will be longer than nighttime until September 25, after the autumnal equinox.

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The National Weather Service contributed to this article

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