To everything there is a season and a time to every purpose under the heaven.
KABOOM! That is the sound of my head hitting my desk after reading Ken Parrot’s latest comment on my blog. What was this comment and why did I find it so mind shatteringly stupid? Before I can answer that we first have to look at what provoked his comment.
Commentator Neil Bates made a rather confused and meandering comment at the end of which he posed the question:
But weren’t there issue with explaining seasons, the whole axis thing? We hear so little about that. [He’s referring to the geocentric model of the world system]
Our courageous Ken P. never one to shirk a confrontation with the evils of geocentrism rushes in with the following answer:
The seasons are well explained by the earths tilt (or the tilt of the “sun’s path” – according to a Copernican model. Most schoolchildren have no problem. But not accfording to a geocentric one.
I am not familiar with how traditionalists explained the seasons at the time. (Like the phlogiston theory the geocentric model is not of scientific interest to science today – more of interest to historians and philosophers, who sometime get the science wrong). But it would have been simply explained by adding another movement to the sun which provided an annual movement with respect to the equatorial plane.
And that was the huge elephant in the room – the need for indulgence in a huge number of artificial ad hoc adjustments to retain geocentricism.
Whatever the traditional explanation of seasons was I don’t think it followed in a natural way from the assumption of geocentricism as they do from a heliocentric model.
Why is all of this mega stupid? Well for a whole lot of reasons actually. Firstly if one knows nothing about a subject, which Ken P. quite happily admits is here the case, then one should do some research before opening ones mouth or one is liable to put ones foot in it. Ken P. actually manages to put both feet in with his boots on.
Secondly the correct answer to Neil’s question had already been given three comments above Ken’s by Rebekah Higgitt. However our hero isn’t interested in reading what other people have to say, it’s eyes closed and head first through the wall of his own prejudices.
Thirdly, and this is the really embarrassing part the geocentric explanation of the seasons far from being ad hoc and unscientific is mathematically identical to the heliocentric one! It’s only the frames of reference that differs. As Ken P. says himself it’s so simple a school kid can understand it. So for the benefit of Neil and Ken I will explain.
Heliocentrism: Axial tilt.
The heliocentric model of the world system say that the season occur because the earth’s axis is tilted by approximately 23° to the plane of the earth’s orbit around the sun, see diagram below:
Geocentricism: Obliquity of the ecliptic.
The geocentric model of the world system says that the seasons occur because the ecliptic (the suns apparent annual orbit around the earth) is tilted by approximately 23° to the plane of the earth’s equator, see diagram below:
Notice something? They are to all intents and purposes exactly the same diagrams because they both refer to the same thing. Axial tilt is even, incorrectly, referred to as the obliquity of the ecliptic.
Even more embarrassing for Ken P. is the fact that in every day language when talking about the solar cause of the change of the seasons everybody, including scientists, actually describe the geocentric model and not the heliocentric one.
The sun’s annual journey (you see its already started geocentric not heliocentric), in the northern hemisphere, begins on about the 21st March when the sun is directly overhead at noon on the equator, the vernal equinox (from Latin equinoxium “equality of night (and day)”). It then travels northwards for approximately ninety days until it is directly overhead at noon on the Tropic of Cancer, summer solstice, whence it turns and starts heading southwards. Tropic comes from the Greek “tropikos” pertaining to a turn i.e. the turning point in the sun’s annual journey. After approximately another ninety days it is directly overhead at noon on the equator again, about the 21st September the autumnal equinox. From here it heads southwards until about the 21st December when it is directly overhead at the Tropic of Capricorn, winter solstice, whence it turns once more and heads back up north.
Now even Ken P. should be able to explain the turn of the seasons in the geocentric world system.
As a footnote Ken P. said in the middle of his answer.
… the geocentric model is not of scientific interest to science today…
Sorry to have to contradict you Ken but all astronomers when beginning their training first learn geocentric astronomy because that is the way that we perforce observe the universe. Also anybody learning stellar navigation, a very scientific discipline, learns geocentric astronomy again because that is perforce the way we observe the heavens.