Tuesday, March 20, 2012

Happy Vernal Equinox (belated)

Happy Vernal Equinox

The most popular opinion on what causes the vernal equinox is that the earth is halfway between its summer position and its winter position. This is right, except that the way in which most people view what it means is quite wrong.

The idea works like this: You have seen the pictures of the earth’s orbit around the sun, right. If not here is one for you to look at. I’ve only drawn the earth and the sun, and I drew them completely out of scale. I’ve tried to use only primary colors, and drawn a happy face on the sun to help you feel less stressed in this busy world we live in.

OK now. Most people (including scientists) know that the earth travels one time around its orbit in one year. The most popular opinion (based on randomly unverified surveys of Utah residents) about the seasons is that they are caused by the earth traveling from close to the sun to very far away from the sun. The sun is hot so it is summer when the earth is close to the sun, and winter when it is far away. I’ve asked a whole slew of folks, and that is what I am told. They know this to be true. They can see the seasons change, and so they have visible confirmation of their knowledge.

Here let me label my picture of the earth’s orbit with the seasons. This is so much fun. It’s like a PowerPoint presentation. Sometimes when I watch PowerPoint presentations I feel like I have died and gone to hell. This proves that there is a hell. SO perhaps if I prayed to Cthulu I would know heaven and come to love long PowerPoint presentations.

The Vernal Equilux is when the day and night are of equal length.  It occurs near the equinox on the calendar, and depends on exactly where you are latitude-wise.

Whenever I have the opportunity to be ‘splained-to about how the eccentricity of the Earth’s orbit causes the seasons I ask about the length of day. This question is often a stumper, but when it is not I usually get the same answer, and it has to do with women in very short skirts.

“It is like an ice skater” the ‘splainer will ‘splain.


“With a very short skirt?” I ask.


“Sure” ‘Splains splainer “When they spin with their arms out, and then pull their arms into their body, they spin faster”


“And their skirt flies up” I reply


“Sure” replies the ‘splainer. “you see it’s like an ice skater, but with gravity”.


“That would explain why so many animals become reproductively receptive in the spring” I add.


“How so?” asks ‘splainer.


“The skirt being halfway up is kinda a tease” I reply.


There is actually something elegant and wonderful about this construct. It weaves a knowledge about conservation of angular momentum with experiential data about what is hot and cold. It is quickly explained, and makes perfect sense. It is such a popular idea that if opinion drove reality this would be an irrefutable truth.

Unfortunately. ..............

If I get a second follow up question it is always this:

“So, if you call someone in Australia, you know, way south of the equator, in July…is it summer or winter for them?”


Some ‘splainers are stumped by this, and explain that they don’t know anyone in Australia. Some tell me that it is always summer in Australia, but my favorite answers are those that build upon the lovely construct that defines the intricate dace of planets and sun that make our seasons. They go on to explain how the planet wobbles as it orbits, and that the wobble causes it to be winter in Australia when it is summer in the northern hemisphere.

Part of the transcendently cool thing about the wobble theory is that it is correct. The other is that the construct now has two mechanisms for creating the seasons. One mechanism for the northern hemisphere, and another for those people south of the equator.

Of course the wobble theory is the mechanism for seasons both north and south of the equator. These days the sun is actually closer to the earth in the northern hemisphere’s winter than it is during its summer. The vernal (and autumnal for that matter) equinox is when the sun is directly overhead of some theoretical equatorial observer. It is an exact moment in time. It occurred today at 5:14 AM GMT.

Missed it? I know I did. Next year it will occur at 11:02 AM GMT on March 20th. Start planning your festivities now, and avoid the shopping rush.

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