It Just Is

James,

Why are you turning the plate. The apple (earth) is spinning like a gyroscope and will not move its axis of rotation so when it reaches the other side of the plate (sun) it will be pointing slightly away from the middle of the plate.

Alasdair

Orreries are wonderful things (I have one sitting next to me as I write this)...

Andy, where are you sitting?

If it's at home, I'm jealous! :)

Alasdair, I'm turning the plate because that represents an object orbiting about the centre, (of the plate). You are correct, 'something' must keep the axis of the Earth pointing in the same direction, (relative to the room), and, like you, I think that is the gyroscopic action of the spinning Earth.


My point is that 'simple' fact is missing from all the everyday explanations of the seasons which makes me wonder if the people who write them know any better, i.e. "It Just Is".


Can anyone come up with other examples?

David, I am indeed! But it's only a very little orrery (only sun, earth, and moon) - I'd love a full one.

I must admit that I'd completely forgotten this bit about the area covered by the suns rays at different heights...
https://en.wikipedia.org/wiki/Effect_of_Sun_angle_on_climate


But regarding simplicity of explanation in school books, as many of you know I've done a lot of voluntary STEM work in schools, and it is a real challenge to make explanations which are "correct" but don't rely on considerable background knowledge. So I do have sympathy with explanations that leave information out, a good explanation needs to be a pyramid that gives the opportunity to get wider and fuller depending on the expertise and interest of the student. I see this from the other side when discussing biology with my daughter who's currently a PhD student, her first response to almost any point on genes, DNA, microorganisms etc is "well, actually it's a bit more complicated than that"!


Interesting point,


Cheers,


Andy

James,

I only mentioned the gyroscope analogy as being a simple corollary that most people can relate to, rather than something "I believe". To quote Andy, "it is a bit more complicated than that"! Even a gyroscope will change its direction of axis if there is a force applied, though not necessarily in the direction of that force.

The reason the axis of the earth remains pointing in the same direction is that there is no major force trying to make it change its direction. However there are forces acting on it and the direction of the axis is actually moving, a feature called the precession of  the equinoxes (see https://www.britannica.com/science/precession-of-the-equinoxes) which causes the direction of the axis of rotation of the earth to wobble with a frequency of once every 25,722 years (give or take a few months...). This means that the signs of the zodiac and their horoscope months no longer align with the constellations which matched when they were first recorded. The vernal equinox, originally when the sun entered the constellation of Aries, has now moved through Pisces and is now in Aquarius, though I suspect that most people who try to explain the seasons haven't a clue about this yet are still happy to talk/sing about "The dawning of the Age of Aquarius"!

There are many explanations which are over-simplified just to make them approachable to the target audience. I still remember my first week at University where we were told that initially we had learned from our parents, then our primary school teachers explained why our parents were wrong and gave us a different explanation. Then our secondary school teachers explained that our primary school teachers were wrong and gave us yet another explanation, and now we were at University where our lecturers would explain why our secondary school teachers were wrong....

From this I would suggest it is always a good idea to challenge accepted wisdom/explanations, but not necessarily to throw them out (otherwise how do people learn if they don't have the underpinning knowledge to understand the full concept).

Regards,

Alasdair

If I had £1 for everytime I've explained to someone why/how we have seasons and why there is such an extreme change in day/night lengths for the UK over the course of a year...! Lets just say I'd be able to afford to go to an equatorial country on holiday where their day lengths don't really change that much (and where it's always summer all year round... )


I agree with you Alasdair Anderson‍, it's ALWAYS a good idea to challenge accepted wisdom and current thinking otherwise we'd never do anything different or create anything new!


It puts me in mind of an argument I once had with my English tutor when I questioned the perception of what is considered a 'classic' piece of English Literature (while studying the Bronte sisters for A level Pure English Literature). "You're telling me that it's a classic but on what authority? You're only saying it is because that's what you've been taught too? Is this really a good piece of literature or did someone decide it was and no one questioned it?" Needless to say they didn't appreciate my opinion...  Personally think it goes back to the Art argument.  We're taught what is 'good' art and what is 'bad' when really we should be encouraged to make up our own minds! 


One of my favourite quotes is "Just because it is, doesn't mean it should be" which drives me to question everything... 


Lisa

Alasdair, I know the Earth does all sorts of 'wobbles' that produce significant change over a long period but am I missing something with regard to what is meant by 'orbit'?


Consider a spherical body in circular orbit. Let's make it very small, the weight at the end of a length of string, would that be in orbit if we whirled it around our head? Consider another identical weight on an identical length of string, shouldn't it behave the same way? Now imagine we were quite good at this and whirled both around our head at the same time but displaced by 100 mm. They should both behave the same way and the distance between them would stay the same. Add a few more weights and strings and they could all be 'flying' in formation, fixed in their local frame of reference, a frame of reference that would be 'in orbit' rotating around the centre. There is a force acting on all these weights, the equivalent of the gravitational attraction between 'the Sun' and all these satellites. Any axis that one chooses to define between these satellites would also be rotating, if you like pointing towards the 'Sun' on the left of the classic season diagram and towards the Sun on the right of the diagram.


All these objects are constantly 'falling' towards the centre and rotating as a consequence, taking their local axes with them. That at least is my understanding of 'orbit'.


Lisa, As the great Doreen Tipton, (look her up!) says "We think therefore we yam!" (Maybe only works for those familiar with Black Country ways!)

James,

I am afraid I don't understand your point with this. The gravitational attraction between the sun and the earth acts (more or less, discounting tidal forces) equally on all of the earth. With your weights and string analogy the force acts at the point the string is attached to the weight. You then lose me with the "Any axis one chooses to define between these satellites". I am not an expert in celestial mechanics but I know enough to understand what is happening to the planets, though perhaps not enough to make a good job of explaining it - which brings us back to your first post, unfortunately.

Alasdair

ps I looked up Doreen Tipton, perhaps I will need to spend a bit of time watching her on YouTube!