Notes: Epicycles and Planetary Orbits

So far you're pretty sure that you're place is the centre of the universe, and that means that everything in the sky is circling you, as well it should, god's own image, Joshua 10:13 etc etc. However you found something that didn't quite agree with that. The strange wandering stars were moving in a way that didn't exactly suggest  a nice clean orbit around us. So you did what anyone who's sense of place in creation was threatened would do. You made it fit your theory.

What you decide is that the planets are still orbiting you, calling that orbit the deferent, however they're also moving in small circles around that deferent. You call these little circles epicycles, literally 'on the circle'. Alright, everything is sorted. These circles account nicely for the changes in direction, velocity and what not that these planets take when orbiting you.

Source

Except they'd go out and observe a bit more and it didn't quite fit. So they'd add more epicycles. Still not quite right. More epicycles! Still no? Just keep changing stuff until it fits our established theory gorramit!

These days epicycles is something of a swearword in science. I can tell you this with certainty because two lecturers in entirely different parts of the world have told me just that. If a theory comes along that builds into something really unnecessarily and ridiculously complicated it may well be compared to epicycles. Then someone gets punched.

Incidentally, this is where one of those fables I keep writing about come in. In fact this is the first one in that first lecture series where I got the whole idea. Basically the idea that they kept making things more complicated is true, but they didn't so much keep adding epicycles as they did arbitrarily change the velocities of the planets, or make the epicycles move side to side, anything that might help get it to work. The end result is the same though. An arcane mess of a theory that you just want to curl up and ignore.

Kitten break.

So you do. You decide you're fed up with this nonsense. Clearly something is wrong, and a new theory is needed. So thought a fellow named Copernicus, who had a look at the data and thought "Ok, this needs some work". So he proposed Heliocentric cosmology, and published his theory in a book called De revolutionibus orbium coelestium, On the Revolutions of the Heavenly Spheres. Initially it didn't sell so well. Copernicus has made it really rather technical, so that only the most learned of astronomers could really understand it. This allowed it to disseminate into their ranks before it roused any of the more zealous geocentric types. Eventually however it did become fairly popular, enough so that the pope had it put on the Index of Forbidden Books in 1616. Copernicus didn't really mind so much at the time, though mainly because he was dead. Probably best. If he was still alive when it was banned he might have been taught the error of his ways, as it were. And then died.

Now this theory works, you think, though probably only in your head, lest you be put on trial for heretical thinking or whatever. It fits the data. The planets all orbit in the same direction, the outer planets take ages to get anywhere, everything fits. What this also means is that we can take a decent stab at working out how far away the other planets are:

I'm tired, hungry, and have been at this all day. You be happy with my illegible scribbles.

So finally, we have some proper idea of our universe. There's us orbiting the sun, along with other planets, and the fireflies that got stuck up on that big bluish black thing.

Next time, the uneventful adventures of Tycho Brahe.

Not that one.

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Notes: Stars and Planets

So far we have made some basic observations, and come to a conclusion about our place in the universe that, as far as we're concerned, is flawless, and frankly kind of gratifying. Centre of the universe huh? Who'd have guessed it. Enough back patting for now though, we have more looking at stuff to do.

For example, the fathomless depths of my eyes.

You may have noticed that while the moon is floating about, it's joined by a bunch of other tiny points of light. To save you the trouble of counting I will tell you now that there are roughly 4000 stars visible to the naked eye. Almost all of these move across the sky in a fixed pattern that, if you were of a type, you might want to sort into patterns and what not.

I am momentarily amused that iTunes, in an act of solidarity has just shuffled in Metallica's 'Orion'. Simple things. Excellent track though.

Alas, things are not as perfect as you might have liked. There are 5 points that don't seem to want to stay in place with the rest. And because you're an ancient Greek, you go ahead and call them astēr planētēs which sounds lovely until you realise it literally means 'Wandering star'. You decide to stick with 'planets' because you're English now and frankly we seem to have a properly hard time not nicking other cultures' words. They are named:

• Mercury
• Venus
• Mars
• Jupiter
• Saturn

Now I'd like to point a little something out. It's not quite so obvious in English where our days of the week are fairly Germanic in origin (There is something quite enjoyable about going to lectures on 'Thor's Day') but some of you may know the more Latin based, French  Check out their names for the days of the week starting on Monday:

• Lundi
• Mardi
• Mercidi
• Jeudi
• Vendredi

Now switch back to English for the weekend and we have:

• Saturday
• Sunday

It all has the same kind of root which is why I'm being fairly inconsistent with language. Point is that our 7 day week is based on the 7 key objects observable in the sky with the naked eye. Some languages name them with their Germanic roots, some Latin, some Gaelic, but on the whole they're all from the same thing, showing just how far back this astronomy business goes.

Right, enough linguistics¹. Back to the observational SCIENCE! So, these wanderers pique your curiosity, and you devote some time to observing them. What you notice is odd. They really do wander, sometimes completely randomly.

A composite view of Mars from Earth

It looped. Mars bloody looped around in the sky. This is nuts. This completely goes against your world view. Everything is meant to be nicely orbiting us and there is Mars pissing off doing it's own thing. What a wanker.  But nonetheless, you have new data to be interpreted. If it's not circling around us neatly it can only mean one thing.

Epicycles.

[1] If I wasn't a physicist I would absolutely go into studying linguistics and etymologies and what not, and not just so I could make hi-LAR-ious oral sex jokes.

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Notes: The Moon

Back onto the astronomy thing. As mentioned last time, we are moving onto the second most obvious thing in the sky, The Moon.

To begin with, it's worth knowing a little about something called the ecliptic. This is basically the path the sun took during the day. Secondly, you need to know that everything has an angular position. There is a brilliant rule of thumb for this. I urge you to try it, it works for damn near everyone. Simply hold your arm out in front of you, with your hand up straight, like a traffic cop telling you to stop or something. Your finger is roughly 1°. With this in mind, know that the Moon can be found within 5° of the ecliptic.

Incidentally, both the Moon and the sun are roughly 0.5°, meaning you can more or less cover them with one finger, though if you want to test this one I'd recommend trying it on the Moon first. The Sun is very formal, and pointing is quite rude.

Alright, so you see the Moon, you observe it over some time, and you notice it changes shape with a certain regularity. These are called the phases of the moon and proceed like so:

Incidentally, in the same manner as with Dara O'Brien's slip up, I had my reservations about the accuracy of this particular advert that some of you may remember from our youth.

That clearly should be "Full moon, Waning crescent, No moon", but I guess marketing departments have no time for scientific accuracy.

Anyway, distraction aside, this cycle repeats itself more or less every 29 days.

Interpretation of the Data

Ok, so you're a blank sheet of potential human observation. Telescopes and what not have yet to be invented and all you have seen so far is the Sun and the Moon, going around and around in an eternal game of celestial kiss chase, one full of fiery passion, the other kinda turning invisible half the time. I don't know, I never played kiss chase.

Using this data you try to craft a model of the universe, and eventually settle on one that fits your Sun-Moon-Earth data perfectly. Thus came about the Ptolemiac system, from which arose much of Geocentric cosmology, a view that persisted for a good 1400 years, and one that has clouded much of western philosophy, religion and science.

This incidentally is fine. It's all very well to look back and scoff about how uneducated past folk are, but do remember that given the data they had, this view fit perfectly  They were using what we might now call a "non-inertial reference frame", which in this case is kind of a nice way of saying they didn't know the Earth was also moving.

I'm not strictly holding to the lecture by lecture notes thing at this point instead opting to separate them into similar sub-subjects. So, I'll cut these notes half way through and next time I'll say a little about stars and what not.

Now if you'll excuse me, I need to go buy some Jaffa Cakes.

Heaven.

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Notes: Thermometric Properties

A thermometric property is one that varies with temperature. For example, most objects will expand as temperature increases. The volume of the object is a thermometric property.

It is from these properties that we get our temperature scales. Now, we can't just measure every degree between 1 and 100. The problem there is that different materials expand at different rates. An alcohol thermometer will not agree with a mercury one. So what you do is you get two points that are definitely what it says they are, then you just split everything in between evenly. Mostly the two points will be the temperature at which water freezes and boils at 1 atmosphere of pressure. Celsius for example used to be defined as such, putting freezing at 0 and boiling at 100 degrees, then defining a single degree Celsius as 1/100 of the boiling point..

These days things are a little more...precise? It's not changed too much but now Celsius handily ties into the Kelvin scale which has the fixed points as absolute zero and the triple point of water, the triple point being defined as the temperature at which a substance (in this case water) can exist as it's 3 phases (solid, liquid and gas) in thermal equilibrium. These points are given the numbers 0 K (-273.15 °C) and 273.16 K (0.01 °C), with a single Kelvin being defined as 1/273.16 of the temperature of the triple point of water.

Incidentally, avid QI fans like myself will remember this particularly contentious issue:


To be perfectly honest, I may not have actually gotten as far as writing in, but I was definitely bothered that he had gotten points for it the first time around.

I'm sorry Mal, I'm just bit sad like that.

Anyway, that was 2 lectures worth of notes. Christ, this particular module drags on a bit.

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Notes(or not): Dynamics, Algebra and Calculus

The problem with these subjects (more obviously for the latter two) is that they are fairly maths based, not to mention how much of it so far has basically been A Level recapping. As such, they don't really translate into typed format very well, and, to be honest, even if they did it's more about practice than information. So, I will not be blindly pumping out equations unless it's particularly interesting. Complex numbers for example, I might do something on them.

But until then, if there's something you think I might help with, and for some reason you can't ask your own lecturer, give me a shout and I'll see what I can do to assist you. Together we will help us help you help us all.

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Notes: The Sun

Part of what makes science kinda great is that it's constantly being worked on and improved, tempered in the forges of experimentation. Astronomy is one of those odd sciences, in that we can't exactly go out and do that. Going up to stars and measuring stuff poses certain logistical problems. So instead what we do is look at stuff. A whole lot. And would you believe that looking at stuff is really gorram interesting? Think about it, it's one of the oldest sciences and it still has a pretty massive presence. Something about the vast expanse of unknown is still sparking the old human curiosity...thing.

Ok, so let's explore what we can observe with just our naked eyes. I mean let's face it, not everyone has an awesome 8" reflective equatorial telescope. And while that is a shame, it's not the end of the world.

For starters if you look up during the day, and are not in Wales, then you may see an incredibly bright thing. We call this The Sun, or Sol, if you're the kind of person who calls the Earth Terra in casual conversation. If you give it a while, you may also notice that the sun takes a path across, and further careful observation reveals that the path the sun takes is a little different every day. In fact this happens all year around, the path being a little bit shorter each day at this time of year until the 23rd of December, or the Winter Solstice.

Source

Side note: You may notice that that is a fairly familiar date. That is no coincidence. Fun fact, the Bible doesn't actually give a specific date for Jesus' birth. Thing is that at their most expansionist, the Roman Catholics decided they needed a date to celebrate the event of their saviour's birth, and they also wanted to get rid of the pagan celebrations of the solstice. And as my lecturer so put it, you don't get popular by cancelling parties. So, the logical thing to do was to co-opt the existing "unholy" celebrations for their own righteous and godly one.

Ok, so that's one glowy orb seen, how about the other? During the night, when they sky is arguably at it's most stunning we have the bright white disk we call the Moon, and that's what we shall cover next time.

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Notes: Thermodynamics

Posts with the heading Notes:[subject] are more for my benefit than yours, just a little something to reinforce what I've already written down. There is only so much I can do to make dynamics a source of humour, for instance. But by all means read on, and I'll certainly do my best to spice things up a little.

Kicking things off with a bit of basic classical mechanics. This is the part that deals with the energy transfer of stuff on the macroscopic scale, that is to say, things we can measure easily enough in a lab. Key word in this area is systems.

A system has been defined for me as a collection of matter in a boundary, though truthfully I prefer Wikipedia's disambiguation page's suggestion "the portion of the physical universe chosen for analysis". It makes it sound like we are undertaking something fairly special, selecting a single part of the entire universe to study and observe, when in fact we are just considering energy transfer in engines and what not.

There are, generally speaking, 3 types of system; we have open systems, where matter can cross the boundary, closed systems, where matter cannot cross the boundary, and isolated systems, where both energy and matter are unable to be exchanged.

Generally speaking CT deals with systems in thermal equilibrium.

Extensive and Intensive properties

Extensive depends on amount of matter in a system
Intensive does not.

Well that was easy.

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