Happy Perihelion!

January 2-3 is the time of the year when the orbit of planet Earth takes us to the closest distance to the sun!


Learn somethin’ new every day :slight_smile:

So strange that it’s the coldest in the Northern hemisphere! :slight_smile:

That’s because the tilt of the Earth’s axis moves the northern hemisphere away from the sun.

As a kid I thought it was odd that there’s snow on mountain tops because they are closer to the sun lol.


We can learn a lot about the sun from They Might Be Giants.

Not exactly, but you probably didn’t want to spend the time explaining it. Anyway, the increased distance from the sun due to its axial tilt isn’t really large enough to account for a significant temperature difference. Winter in either hemisphere is due to the axial tilt away from the sun causing (1) the sunlight to strike that hemisphere at a shallower angle and (2) the decreased length of daylight hours. The opposite happens in summer when daylight hours are longer and solar radiation hits the hemisphere at a steeper angle.

Like’s been already mentioned, the Earth is at perihelion (closest to the sun) during the northern hemisphere’s winter and furthest from the sun (aphelion) in the northern hemisphere’s summer. The opposite is true in the southern hemisphere where their summers coincide with the planet being closest to the sun and furthest away in their winter.

Using the inverse square law to do a little math, it turn out that the difference in solar radiation hitting the earth between perihelion and aphelion is about 6.88 percent, which seems significant.

So with all that being the case, it would stand to reason that since the Earth is closest to the sun in the northern hemisphere, winter should be warmer and summers should be cooler relative to the southern hemisphere where winter coincides with being further away from the sun and summers being closer. Right? Nope. For that matter, the opposite seems to be true.

Here’s why (at least it’s the most important of several reasons). It has to do with the oceans, which take longer to warm up in the summer and cool down in the winter. In other words, they serve as a moderating influence on the Earth’s temperature swings from summer to winter. The southern hemisphere has a higher ocean-to-landmass ratio than the northern hemisphere, so the winter-to-summer temperature swings in the southern hemisphere are moderated more than they are in the northern hemisphere where the ocean-to-land ratio is lower.

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It may also be interesting to note that the opposite … as in the furthest distance away from the sun … is called the Aphelion … which, and this is the part that I like, usually occurs somewhere on or very close to July 4th.

No coincidence that that exact date was chosen by the 13 colonies to declare their independence!!!

Just sayin’ :wink:

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