Thursday, September 16, 2010
Geo-xcentricities; you too can be Galileo with just a pair of binoculars (and gaffer tape)
Other people, especially Ethan at Starts with a Bang and the Bad Astronomer, have dealt with the technical details (and I have an earlier discussion here and here). My goal is to get you, the ordinary person on the Clapham omnibus (or in my case, the Outer Harbour train, where I am writing this), to try and demonstrate the Earth is heliocentric for yourself and to do so with common household materials. After all, science is at heart a practical endeavour, and non-professionals should be able to find the evidence for themselves.
So for this journey into the starry spheres, we will need a pair of binoculars, a camera tripod, some cardboard and alfoil, and lots of gaffer tape. We also have some luck, as the sky is currently cooperating in the Geocentrism debunking stakes.
First we have to ask ourselves, which “geocentric” theory are we disproving. The classic geocentric theory is that of Ptolemy, in which the planets, Moon and the Sun all orbit the Earth. The most famous variant of this is Tycho Brahe’s helio-geocentric system, where the Sun and Moon orbits the earth and everything else orbits the Sun. There are important differences in the systems which we will explore later.
First off, let’s look at the phases of Venus. For this you will need binoculars and the camera tripod. You will also need a way of attaching the binoculars to the tripod. These days I use a special attachment (but this requires modern binoculars that have a screw thread on the body), but in the past I have used gaffer tape to good effect. Why attach the binoculars to the tripod? Because otherwise there will be too much shaking for you to see the image properly.
The image to the left is the setup I use for observing Sunspots (we come to that later), showing the binoculars gaffer taped to the tripod.
At the moment, Venus is prominent above the western horizon. Point your binocular lash-up at Venus, in my 10x50 binoculars Venus is very small but is a disk which has a distinct “half –Moon” shape. If your binoculars don’t have decent anti-glare coatings, you may have to observe in the early twilight in order to see Venus’s shape without internal reflections from the binocular lenses getting in the way.
As you watch over the coming weeks, you will see Venus expand in size and become more crescent- shaped. Sketch the shape so you can follow its progress. This is so fast you should see a visible change in just one week. By mid-October Venus will be a thin crescent almost 2/3rds bigger than when you started observing. By late October Venus has nearly doubled in size and is a thin, glistening wire. Then Venus vanishes into the Suns glare and reappears in the morning. Over the next few months you can watch Venus shrink and become a tiny disk.
And now you have demolished the Ptolemaic geocentric system. Venus does have phases in this system, but quite unlike what you see here (I leave it too the reader to work out what a Ptolemaic systems Venus phases would look like, you can see a model of Ptolemaic Mercury here, which will give you a good idea). And you have only taken almost 6 months to do it (what, you thought it would be easy). As a reward, here's an animation of the Phases of Venus.
Left image Jupiter above the eastern horizon, Right Image, Venus above the western horizon, both at the same time in the evening (around 8pm ish in mid September 2010).
Jupiter and three of its moons imaged with a mobile phone.
But Ah! The Medicean Stars, now known as the Galilean Moons, they will shuttle backwards and forwards during the nights as you watch. The realisation that these “stars” were Moons of Jupiter were not a blow to any form of geocentrism per se, although they were the second of a series of powerful blows against the Aristotelian physics that underpinned Ptolemy’s system, which aided its demise. Determining that these specks actually orbited Jupiter, and were not just accidentally there, took a lot of effort.
Try keeping track of these sparks, and without reference to an almanac, try and determine their orbits (heck, try and keep track of which near identical points of light are which). It may take a while, you will need to keep careful sketches, and track the Moons and Jupiter with respect to the stars as Jupiter moves through the heavens, but a) You are sketching Venus anyway and b) it will be well worth it (hey, you proving things for yourself!).
The next bit is more demanding. The Phases of Venus demolished the Ptolemaic Geocentric system, but the Tychonian- Geo-heliocentric system had Venus phases just like a pure heliocentric system (which is not surprising, as Tycho’s system is an inverted Copernican system). To eliminate the Tychonian system, we need to observe sunspots.
Luckily the Sun is coming out of its quiet phase, so you will have some to record. For this you will need to set up a safe binocular projection system (as shown above), where the image of the Sun is projected onto a surface so you can record the Sunspots. NEVER LOOK DIRECTLY AT THE SUN WITH BINOCULARS AS SEVERE EYE DAMAGE WILL RESULT.
Anyway, while you are recording the Phases of Venus and the orbits of Jupiters’ Moons, record the passage of Sunspots over the Suns face, over the 5-6 months you are recording the susposts, you will notice the path taken by the sunspots moves up and down. This is due to the Earths orbit not being exactly in the plane of the Suns rotation. In a geocentric system, with the Sun orbiting the earth once a day, this variation would show up on a daily basis, but what you observe can only be seen in a heliocentric system.
So, congratulations, you have just demonstrated that geocentric models don’t describe the solar system we see using very simple tools. It took a while, and was hard work, but you have demonstrated it yourself, and all the blovation of geocentricists won’t take that away (yes, Stellar parallax gets all the glory, but annual Sunspot variation was a powerful blow to Tychonian geocentric models). If you want to, you can take this further by making your own Foucault's Pendulum.
I don't know whether such a system was ever proposed by the followers of Tycho's view which remained popular deep into the 17th century; anyway, historians of science take the discovery of the aberration of starlight by Bradley in 1728 as the first direct proof of heliocentrism. And Bessel, who first measured the parallax, said so himself.
Bradley's insight was not needed to kill off Tycho anymore, though, as Kepler's understanding and Newton's explanation of the planetary orbits in 1689 had made it clear to those listening that everything works so much better with the Sun in the center. A 2003 article by O. Gingerich explains all that very well.
Well, once you have a rotating Earth it's no longer a Tychonian system (Tycho abhorred the idea of any motion of the Earth, and there is no good theoretical reason to tack on a rotating Earth), and because it is no longer an inverted mapping of the Copernican system, you have other problems. Certainly, anyone who was wielding Occams razor would look askance at the rotating Earth-Geo-heliocentric system (A Japanese astronomer did propose a system like this).
Sure you can come up with any range of weird ad-hoc tack-on's to Tycho's scheme, but Tycho's scheme itself was dead in the water with the solar sunspot annual variation.
pAnd People did come up with a whole range of weird versions of Tycho's sytem (eg. only Mercury and Venus orbiting the Sun, everything else orbiting Earth or common centre), but such ad-hoc modifications were never popular (for obvious Occam's Razor reasons).
Acceptance of the heliocentric Keplerian/Netonian scheme was patchy, rapid in some areas, and slow in others (like Scandinavia).
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Um ... that can only mean that the Sun is at the centre of the Earth. :-)
So here are two comentaries on heliocentric arguments, strangely and wrongly neglected, though the observations aren't such as one can make entirely for oneself.
First, we all know that neither stellar aberration nor parallax could have been observed in 1633, for lack of good enough instruments. And a Foucault pendulum, though possible to construct, required a theoretical analysis that exceeded the analytic tools available to Galileo. But there is a perfectly simple demonstration of terrestrial motion, available in the 17th century without a single improvement in technology or analysis: large-scale fluid motion.
From, say, 1550 onward, the ocean currents could have been roughly mapped if anyone had tried. It seems not to have occurred to anyone until a notorious Elephant's Child from the American colonies crossed the Atlantic a couple times, pestered the sailors with questions, and later wrote about the Gulf Stream.
It would have been harder, but still possible, to gather data about prevailing winds. And the first person to see that there was non-obvious stuff about winds, like winds from the East in a storm that was moving West was that same Benjamin Elephantson Franklin. Without a proper analysis of the Coriolis force, anyone who has understood inertial efects could have seen why the currents move in opposite directions in the two hemispheres!
Why do I seem to be the only person who ever thought of this as a low-tech demo available back then if only anyone had asked the questions?
Well, this is much too long, so I'll say more in another comment, pausing only to note the oddity that Galileo wanted to make his demonstration based on the motions of the waters, but he chose the wrong motions.
In fact, it's even stronger than you've mentioned. As you say, the apparent motion of sunspots slopes sometimes upwards, sometimes downwards. But it's better than that: the motions are curved (at most times), as you'd expect from things on a rotating sphere. And the curve is sometimes concave upwards, sometimes the reverse.
If you're moving around an object with a fixed axis of rotation, and you're out of the plane of its equator, this is exactly what you'd see. If you're not, then you can still kludge together some complicated motions, arbitrarily correlated, to account for it (as you can with the other sunspot motions), but who would want to?
Though Galileo used these motions in the Dialogue, and they were among the best arguments there, he did not discover them, and thereby hangs a tale.
Among the people denouncing the Starry Messenger and attacking it on religious grounds was one Franceso Sizzi (1585? - 1618). His book, the Dianoia, was an object of derision to the Jesuit astronomers, who by 1611 had confirmed most or all of the reports in the Messenger. Galileo's friends wanted to see him write one of his fine argumentative blasts at the foolishness, but Galileo "went so far as to apologize for Sizzi and said he had rather have his friendship than triumph in a quarrel with him." [Galileo at Work, Stillman Drake]
Only two years later, Sizzi had turned favorable to Galileo's ideas and sent a description of some new sunspot observations to Galileo's friend Orazio Morandi, who forwarded them to Galileo. It took Galileo some years to see the significance of these, but they are the basis of the sunspot argument he gave in the Dialogue.
Cast your bread upon the waters, and all that.
Everyone knows that a writer should Show and not Tell, but I'm not a good writer, so I'll mention how oddly this episode fits with the image of Galileo as an old meany whose rudeness alienated all his friends, as do other incidents throughout his life.
"....record the passage of Sunspots over the Suns face, over the 5-6 months you are recording the susposts, you will notice the path taken by the sunspots moves up and down. This is due to the Earths orbit not being exactly in the plane of the Suns rotation."
(It is, from the Tychonian viewpoint, due to the Sun's orbit not being exactly in the plane of the Earth's equator. As Einstein has already told us, the two cases are precisely the same, in terms of relative motion).
Think about it for a moment.
We are watching the Sun move, day after day, across the Earth's sky, and it appears each day on the horizon at a point slightly different from the point at which it appeared the day before.
Therefore the sunspots will *of course* also move just that same slight tiny little bit up or down every day, *since the Sun is doing exactly the same thing*!
But the observer would not *notice* the movements of the sunspots in his viewing apparatus on a daily basis, since they are so small.
Only over the 5-6 month period would the movement up or down of the sunspots (and hence, of course, of the *the Sun itself*) have become significantly noticeable.
What we have just described is a little thing called "the seasons".
We don't notice the change every day, but over six months we certainly notice that the day is much longer or much shorter, and this is *all that the author's experiment shows*!