Exposing PseudoAstronomy

December 24, 2013

The Reason for the Seasons

Filed under: astronomy,general science — Stuart Robbins @ 6:46 pm
Tags: , , , ,


As the majority of the world’s population celebrated the Winter Solstice a few days ago, a smaller number of persons celebrated a different event, the Summer Solstice. And yet, polls seem to show that somewhere around 20-60%* of people don’t seem to know what causes the seasons, and the statement I made in the first sentence would have them scratching their heads in confusion. Since this is the Exposing PseudoAstronomy blog where the original intent was to cover common misunderstandings and even media mistakes in astronomy, I thought I’d do a post on this.

*Poll 1, Poll 2, Famous 1980s video of Harvard Graduates.

Proximity to Sun

The most common thought is that seasons are caused by Earth’s changing distance from the sun. After all, Earth has an orbital eccentricity of 0.0167, meaning that from its average distance of about 149.6 million km from the sun, it actually varies between 147.1 million at its closest and 152.1 million km at its farthest. “Obviously,” the thinking goes, “this distance change should affect temperature!” It’s a whopping 5 million km.

And it does. Very slightly. Mars, with its higher eccentricity, has significantly warmer southern summers than northern summers because of this.

But on Earth, the day during which we are closest to the sun is around January 2, and it is farthest from the sun around July 5.

If you’re close to a heat source, you should be warm, right? But doesn’t winter happen in January for the majority of people around the world?

Therefore, this can’t be the cause.

What also doesn’t make sense for this explanation is that the northern hemisphere experiences the opposite seasons as the southern hemisphere. Though, many people are not that well traveled and wouldn’t know this from first-hand experience. However, being in Australia right now, and wearing shorts and a t-shirt, I can guarantee you that it is warm down here. Last week, it was around 40 °C, or about 105 °F. I took my friend’s nephew to the beach.

Earth’s Tilt

The only thing that can explain why a spherical object would experience different seasons in one part than another, at the same time, is if it has something not to do with something that applies to the entire object (like distance to the sun), but rather something that applies to one part and then the other, and can’t apply to both parts at the same time in the same way.



The solution is Earth’s tilt. Earth rotates about its axis, and it orbits around the Sun. Earth’s rotational axis is tilted relative to the path around the sun by about 23.5°. The explanation for seasons is given in the diagram above and has to do with the directness of light. Take a flashlight and aim it straight at a wall. You have a certain amount of light, and it’s spread over a small area. Now, aim it down but still at the wall. You have the same amount of light, but it’s spread over a larger area.

The same thing happens with the sun’s light. When the northern hemisphere is tilted more towards the sun, such as in June, the light from the sun strikes it most directly. But, the same quantity of light is spread over a larger area in the southern hemisphere. That given packet of energy cannot heat a wider area the same amount, so it is cooler. Six months later, same thing happens, but in reverse for the hemispheres.


The reason for this post is that I’m here in Australia and it’s warm. A few days ago was the Winter Summer Solstice, the longest day of the year. I didn’t experience the shortest day this year. And I kept having to correct myself a few days ago, just as above, because it really is hemisphere-dependent.

Similarly, right now it’s about noon on December 25, Christmas from TomorrowLand. For someone who grew up and lived his entire life except for 2 weeks (so far) in the northern hemisphere, it does not “feel like” Christmas (despite being an apathetic atheistic agnostic, everyone except perhaps in China and North Korea cannot help but be inundated by Christmas stuff). It’s warm. It’s sunny. I’m <1 km from the beach and last night I walked outside after dark with shorts and a t-shirt on.

It's amazing how many of our experiences are driven by the weather and climate, and how northern-hemisphere-centric many of us are. Even our emotional state and how we feel about certain events are tied with the weather. And yet, the larger, yearly cycles of seasons, are so poorly understood by hundreds of millions of people.

December 20, 2013

Podcast Episode 96: The Star of Bethlehem: A Skeptical View with Aaron Adair

When Jesus was born
The Star of Bethlehem told
The way. Maybe not?

For the first episode of several interviews, and the last episode of 2013 (Julian calendar), I give you an interview with Aaron Adair who is a recent physics Ph.D. awardee from THE Ohio State University. If you’re wondering “What on Earth could POSSIBLY be new about this?” you’re not alone — it’s the first question I asked him. The interview runs about 45-50 minutes and there are no other segments.

And Australia is fun! Nothing has killed me yet … so far …

December 12, 2013

Podcast Episode 95: The Fake Story of Planet X, Part 8 – Zecharia Sitchin, Revisited

Is Zecharia’s
Planet X supported by
Recent discov’ries?

I revisit one of the classics in this episode, the Planet X claims of Zecharia Sitchin. This is NOT an episode where I specifically refute Sitchin’s claims. Rather, I go through some of the current events (current a decade ago) that Sitchin wrote about and claimed were evidence that his Nibiru exists. This was actually prompted by a recent e-mail that I had received and was BCC’ed to Michael Heiser (who will be a guest in Episodes 97 and 98, to be released in early January 2014).

As with last episode, I also managed to fit in a short Q&A and Feedback, though the Puzzler is repeated from last episode and the solution will not be discussed until, probably, Episode 101.

I’ll remind everyone that I will be at the Launceston Skeptics in the Pub on January 2, 2014, where I’ll be talking about the Lunar Ziggurat saga, not only from a skeptical point of view, but from an astronomical one as well as from a more social science point of view — dealing with “the crazies.” I’ve also actually put fingers to keyboard and typed out the Intro in what may be my first eBook, currently with the working title, “Tilting at Monuments on Mars.” I also plan to do one on Planet X, , and I may finally work on some of the planned podcast-related videos while I’m on vacation in Australia.

December 1, 2013

Podcast Episode 94: Error and Uncertainty in Science

Episodes. Hopefully not
A boring topic?

Another unconventional episode, this one focuses on terminology and what is meant by “accuracy,” “precision,” “error,” and “uncertainty” in science. And, especially, different sources and types of error.

The episode also – surprisingly given my time constraints right now – has all of the other usual segments: Q&A (about asteroid Apophis), Feedback about the Data Quality Act, and even a Puzzler! (Thanks to Leonard for sending in the puzzler for this episode.) And the obligatory Coast to Coast AM clip.

I also talk a bit about meetup plans in Australia, especially the Launceston Skeptics in the Pub on January 2, 2014, where I’ll be talking about the Lunar Ziggurat saga, not only from a skeptical point of view, but from an astronomical one as well as from a more social science point of view — dealing with “the crazies.” I have not yet started to write the presentation, but I personally think it’s fascinating, how it’s playing out in my head.

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