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Illustration of divergent, convergent and transform plates

Tectonic plate interaction boundaries

Divergent (Mid-Atlantic ridge, The Rift Valley), Convergent (The Andes, The Himalayas) and Transform (San Andreas fault, Dead Sea Transform). There are some sub-varieties but these are the main ones. This makes natural sense, so there’s no remembering to do, when you have two contacting plates: they can either be pushing together, pulling apart or rubbing past each other. Incidentally, the idea that the giant continents move around all the time, enough to pull apart South America and Africa, and thrust up the Himalayas, obvious as it may seem now, was once not at all obvious. And if you stand on the ground in a big landscape, it’s kind of amazing to think of just what an amazing notion it was to propose. I read about it in Bill Bryson’s, A Short History of Nearly Everything for which I found a relevant excerpt online - The Earth Moves (pdf) - should you be interested in the characters that had the courage to seriously propose it.…Divergent (Mid-Atlantic ridge, The Rift Valley), Convergent (The Andes, The Himalayas) and Transform (San Andreas fault, Dead Sea Transform). There are some sub-varieties but these are the main ones. This makes natural sense, so there’s no remembering to do, when you have two contacting plates: they can either be pushing together, pulling apart or rubbing past each other. Incidentally, the idea that the giant continents move around all the time, enough to pull apart South America and Africa, and thrust up the Himalayas, obvious as it may seem now, was once not at all obvious. And if you stand on the ground in a big landscape, it’s kind of amazing to think of just what an amazing notion it was to propose. I read about it in Bill Bryson’s, A Short History of Nearly Everything for which I found a relevant excerpt online - The Earth Moves (pdf) - should you be interested in the characters that had the courage to seriously propose it.

27 May 2015

Sales aren’t always the bargain they seem

This could happen to you. HT: Avraham Byers…

20 May 2015

Prospect theory

Dan Kahneman and Amos Tversky’s behavioural economics theory modeling how we make decisions. It illustrates, among other things, some of the non-rational decisions we make as we are guided by emotion and heuristics in decisions. The sketch points out a few of the key points: Loss aversion - the different shape of the curves as we make gains or losses (either side of the centre) represents how a loss of £100 annoys us much more than a gain of £100 gives us pleasure. Diminishing sensitivity - the levelling off of the curves represents that we’ll enjoy winning £100, if we only have £100, much more than we’d enjoy winning £100 if we had £900. Adaptation level - We don’t evaluate from some absolute level - we evaluate whether something is good or bad from a neutral reference point that we adapt to. So, by the end of a movie the movie theatre doesn’t feel dark, yet walking out feels blinding. Your reaction to the £100 example above was probably affected by whether you think £100 is a lot of money or a little, which is all to do with your adaptation level.…Dan Kahneman and Amos Tversky’s behavioural economics theory modeling how we make decisions. It illustrates, among other things, some of the non-rational decisions we make as we are guided by emotion and heuristics in decisions. The sketch points out a few of the key points: Loss aversion - the different shape of the curves as we make gains or losses (either side of the centre) represents how a loss of £100 annoys us much more than a gain of £100 gives us pleasure. Diminishing sensitivity - the levelling off of the curves represents that we’ll enjoy winning £100, if we only have £100, much more than we’d enjoy winning £100 if we had £900. Adaptation level - We don’t evaluate from some absolute level - we evaluate whether something is good or bad from a neutral reference point that we adapt to. So, by the end of a movie the movie theatre doesn’t feel dark, yet walking out feels blinding. Your reaction to the £100 example above was probably affected by whether you think £100 is a lot of money or a little, which is all to do with your adaptation level.

14 May 2015

The Southern Cross to find South: Star chart showing how to find South in the Southern hemisphere using star groups called the Southern Cross and The Pointers

Use the Southern Cross to find South

Where the Northern Hemisphere simply allows you to find the North Star, around which all the stars will rotate, finding your way in the Southern Hemisphere is a little more involved. Unlike in the North, there’s no obvious star due south in the Southern Hemisphere. Instead, you have to use two handy indicators: the Southern Cross — easily spotted, fortunately — and two stars known as The Pointers. Find where these intersect, as in the sketch, and you’ve found due south. Or, if you prefer, you can follow the direction the Southern Cross is pointing for a distance equal to 4.5x the length of the Southern Cross to arrive at the spot. Incidentally, I wondered about reliable methods of finding south in the Northern Hemisphere and north in the Southern Hemisphere. And I think the answer is to find north or south and turn around.…Where the Northern Hemisphere simply allows you to find the North Star, around which all the stars will rotate, finding your way in the Southern Hemisphere is a little more involved. Unlike in the North, there’s no obvious star due south in the Southern Hemisphere. Instead, you have to use two handy indicators: the Southern Cross — easily spotted, fortunately — and two stars known as The Pointers. Find where these intersect, as in the sketch, and you’ve found due south. Or, if you prefer, you can follow the direction the Southern Cross is pointing for a distance equal to 4.5x the length of the Southern Cross to arrive at the spot. Incidentally, I wondered about reliable methods of finding south in the Northern Hemisphere and north in the Southern Hemisphere. And I think the answer is to find north or south and turn around.

7 May 2015

Find the North star

In the Northern hemisphere you can use this handy technique to find the North star, or pole star, that is always almost due North. Follow the last two stars of the Big Dipper, known as the plough in the UK, to a prominent star. Handy for a navigation sanity check at night. The North star is the star that stays fixed in those neat star trails photos with all the stars rotating in a circle as the earth turns. In the Southern hemisphere you can use the Southern Cross and the Pointers to find South, but it's not quite as simple as in the North. …In the Northern hemisphere you can use this handy technique to find the North star, or pole star, that is always almost due North. Follow the last two stars of the Big Dipper, known as the plough in the UK, to a prominent star. Handy for a navigation sanity check at night. The North star is the star that stays fixed in those neat star trails photos with all the stars rotating in a circle as the earth turns. In the Southern hemisphere you can use the Southern Cross and the Pointers to find South, but it's not quite as simple as in the North.

30 Apr 2015

Pole star

Aligned with Earth’s axis of rotation. Appears largely fixed above the poles. The Northern Hemisphere has a Pole Star that will point you North, and the Southern hemisphere’s Pole Star will point you towards South. Handy. Also responsible for some great photography worth checking out.…

23 Apr 2015

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