I know what some of you may be thinking: Pair-a-what now?!
Welp! With Christmas behind us, and New Years Eve done, too, I wanted to take a minute to help everyone celebrate another fun day: Perihelion!
What is Perihelion? Simple! It is when the Earth is closest to the Sun.
Yeah. No joke. We are closest to the Sun 14 days after the Winter Solstice.
But Nick! Wait just a second! It has been so COLD recently, though!
No denying that!
But Proximity to the sun as we zoom around it, isn’t the only driver of how warm things get. We may all joke about being “close to the Sun” in the Summer when we, in the Northern Hemisphere, are very, very warm… But at that time we are actually furthest from the Sun! When that happens it is called Aphelion. That occurs 14 days after the Summer Solstice.
So:
Peri – helion: Close (about 91.4 million miles from the Sun
Ap – helion: Far (about 94.7 million miles from the Sun)
But the truth is that proximity isn’t the only driver of temperature. The tilted axis of the Earth’s rotation plays a role, too. And, truly, an even bigger role.
Tilted… Sun low
It is the axial tilt that gives us warm and cold seasons.
“Seasonal weather patterns are shaped primarily by the 23.5-degree tilt of our planet’s spin axis, not by Earth’s elliptical orbit,” George Lebo, a professor of astronomy at the University of Florida, explained in an article on NASA.gov. “During northern winter the north pole is tilted away from the Sun. Days are short and that makes it cold. The fact that we’re a little closer to the Sun in January doesn’t make much difference. It’s still chilly — even here in Florida!”
Because the Earth is tilted, we get to live through two distinct seasons and two in-between seasons. Summer and Winter – when the Earth’s axis is either tilted toward or away from the Sun. And Spring and Fall, when the Earth axis isn’t a factor at all, and is pointing straight up and down.
You may say, a 23.5-degreee tilt doesn’t seem like enough to change the weather. But it is 23.5-degrees on a ball that is 25,000 miles around! So the amount of solar radiation that reaches the earth’s surface changes pretty dramatically as out tilted earth cruises around the Sun.
This year, the Earth will reach Perihelion on January 4th. In my opinion, this should actually be the start of the new year. But it can’t be. Not because the calendar can’t be changed, but for a very, very cool reason.
And the Earth goes by like, ‘nnneaarrrrrooooommmm’
So, it turns out that the year isn’t 365 days long. According to math, physics, and super smart astrophysicists, the Earth rotates once every 23 hours, 56 minutes and 4.1 seconds. And since the Earth is about 25,000 miles around it means the earth is rotating at about 1,000 miles per hour.
That leaves some leftovers at the end of every year. That is why we have Leap Days! The year ends up being about is 365.25 days long. about 8766 hours. A calendar year, though, is 8760 hours.
And because there are six hours floating around, we run into an issue where the Perihelion falls on a different date – either January 4th or 5th – depending on the year.
And even the orbital shape changes about every 100,000 years. So that changes what date the Perihelion falls on over time.
And a lot of folks probably didn’t realize this, but back in 2020, the perihelion and the preceding 2019 aphelion correspond to the closest and farthest perihelion and aphelion of the 21st century.
The difference was so meaningful that when NASA took a picture of the sun they noticed about a 3-percent chance in the size of the star in the photograph!
Driver of the riders
You know, I lied to you a bit. But it wasn’t to be deceptive, it is because the truth is fun, but not terribly significant when it comes to explaining the seasons, perihelion, and the rotation around the Sun.
I know I mentioned that the Earth orbits the Sun above, but did you know that the Earth doesn’t actually orbit the Sun? And the Moon doesn’t actually orbit the Earth, either!
The driver of orbital motion isn’t just one body orbiting another. Instead, two objects always orbit around a common center of mass/gravity.
In our case, because the Sun it very large relative to the Earth, we just say the Earth goes around the Sun. But we don’t. We both orbit a shared common point of gravity. It just happens to be very, very, close to the center of the Sun.
But the Moon, Luna (that’s its name and why everything related to the moon is “Lunar”), and the Earth (Terra, also, its name, and why you talk about Terrain when looking at a landscape) share a common center of gravity that isn’t very, very close to the center of the Earth because the two celestial bodies are so close in size. Instead, the common center of gravity is about 1000 miles below Earth’s surface..
Here is a brief mathematical explainer…
Gravity! That is also the reason we are all stuck to earth. Earth is very big, and we are very small. So we are ‘orbiting’ a common center of mass/gravity. But that place is so very, very, very close to the center of the earth and because are pulled down around that point, it means we are stuck onto Earth’s surface.
But if you and a friend put on space suits and went into intergalactic space, you would end up orbiting a common center of mass/gravity, and one person wouldn’t just orbit the other.
Lightning to your mind
Now that you have a bunch of fun astronomical knowledge, you can go forth and enjoy your day knowing that the sun is a little brighter today than it is in July.
Or, as put by Dr. James O’Donoghue, “We’ll be 147.1 million km away versus 152.1 million km at our farthest (4 July 2022). The Sun looks 3.6% bigger and is 7% brighter.”
