## Monday, 29 May 2017

### My Visiting Scientist talk

One of the fun things I do is to be the "visiting scientist" at a local primary school, and I am to give a talk to stage 3 later this week. What follows is an outline of what I will probably say, though I still need to cut a bit. That said, any savvy adults wishing to chip in with comments, or, in particular, detected errors, go for it.

There are quite a few salient links here, and there is also some additional material, because I will encourage my students to read this, when they are ready.

My basic brief was to show them how other cultures helped us learn about the night sky. If you know me, you will know that I stand up for respect for other cultures.

Really, I am in the school to support all four STEM areas, but if you don't know the jargon, that's Science, Technology, Engineering and Mathematics, and I like to at least give them all a bit of a canter.

I plan to begin my talk by explaining that I turned 21 last month. What I only explain later is that I am counting in base-36. I do explain that mathematicians use notation a lot, and I mention factorial numbers. If you don't know them, factorial 6 is written 6! and that means 6x5x4x3x2x1.

I add that mathematicians use lots of notation, and any mathematician seeing this, would immediately confirm that mine is a correct mathematical statement.

I then move on to observe that STEM is like a four-legged elephant: "Take away one leg and it may fall over." This goes with a pic that is part of my nod to technology: you can find any picture you want on the Interwebs.

That elephant lost its leg to a land mine, a nod to the fact that technology can do bad things, but other technology can fix the harm.

STEM is always about HOW COME? and WHAT IF? and that leads me into a verse that most of those I have ever taught have seen and heard (and the more perceptive reader will note that the elephant theme is still running):
I KEEP six honest serving-men
(They taught me all I knew);
Their names are What and Why and When
And How and Where and Who.
That is from Rudyard Kipling's 'Just So story' called  The Elephant's Child, which most people refer to as How the Elephant Got its Trunk.  In summary, it goes something like this:
•   The Elephant’s Child always asked questions, and people spanked him;
•   He wanted to know what crocodiles eat: each one he asked spanked him;
•   The Kolokolo Bird told him to go to:
•         the great grey-green, greasy Limpopo River, all set about with fever-trees,
Kipling was a delightful writer for children like me, with the elephant's old nose being a mere-smear nose, which got stretched, and mere-smear nose repeats over and over, as does the great grey-green, greasy Limpopo River, all set about with fever-trees, but the bit I always loved was him saying:

'Led go! You are hurtig be!' Why?  Look at the picture above.

As Kiplingites will know, there is more to the story: if you aren't a Kiplingite: go to this link.

Why do I go off on this tangent? Well Kipling's 'Just So' stories tell us one version of how things began, but they may not be entirely reliable, and science has its own Just So stories.

For example, we say that Mendel discovered genetics, but anybody who has read my Not Your Usual Science Quotations will know about an account that Pierre de Maupertuis wrote about a family with six digits: here is an abbreviated version:
Jacob Ruhe had six digits on each hand and foot, as did his mother Elisabeth, and her mother. Four of Elisabeth’s eight children had six digits. Jacob Ruhe, one of the six-digital children … had six children; two boys had six digits …
So clearly, there was genetics before Mendel, and now, you might think I was ready to start on astronomy, but infuriatingly, I move back into numbers:

Thinking about the Ruhe family, if we had six fingers and six toes, would our counting be based on tens or dozens?

Then I demonstrate how we can count in blocks of five, with the help of an assistant, before revealing this truism on the right.

No, I won't explain it here, either but I do mention some reading (left) that they can do when they are older. My point is simply that we can count in other systems, if we wish. And why does this matter? Well, blame the Babylonians.

I filched this pic from Wikipedia (right), but it is just to show why we measure angles and time in a base-60 counting system.

Now, we really are getting close to astronomy, space and all that stuff. We begin with the shape of the Earth, which most of us think is a sort of sphere.

Did Columbus invent the idea of a planet that was round?  No, of course not: that's just a Just So story, made up by people who knew no better, passed on by modern ignorami.

Some 2000 years before Columbus, the old Greeks knew our planet was a sphere (even though they didn't realise that it was a planet). They knew the shape because:
• things always fall towards the centre of the Earth;
• they saw the Earth's shadow on the moon in a lunar eclipse;
• things further away disappear over the horizon; and
• they could measure the size of the globe.
Pythagoras was probably the first to say that our planet is more or less spherical, but most Greek philosophers mentioned the shape at one time or another. Aristotle knew about it, and Archimedes clearly knew it, given his Proposition 2:
The surface of any fluid at rest is the surface of a sphere whose centre is the same as that of the Earth.
Even Herodotus (c. 485-425 BC), the first historian, seems to have had a hint of the evidence. He described a circumnavigation of Africa by Phoenicians, and how they saw the Sun to their north when they passed around the southern tip of Africa.
These men made a statement which I myself do not believe, though others may, to the effect that as they sailed on a westerly course round the southern end of Libya [Africa], they had the sun on their right—to the northward of them. This is how Libya was first discovered to be surrounded by sea...
In the 2nd century AD, an astronomer called Ptolemy summed up the evidence: as you sail north, the Pole Star is higher in the sky; eclipses of the moon are seen at a later hour in the east than in the west, and the differences are proportional to the distances east or west. When you sail toward a mountain, you see the peak first. The Earth always casts a circular shadow on the Moon during a lunar eclipse, and if that isn’t enough, the sphere was the most perfect shape imaginable.

When you put together all of these, the Earth just had to be a sphere, or close to it. Cylinders, flat and concave surfaces just did not measure up. Now all the Greeks needed to put the whole question to bed was a way of measuring the world. The problem was that they could not get a large enough tape measure, and even if they could, trees and mountains would get in the way!

The measuring bit involves another Just So story, because in the official version, Eratosthenes measure an angle of 7°12', which is 1/50 of a circle, but they didn't have protractors then, and we still can't be that precise with just a protractor.

My guess is that Eratosthenes cut out a wedge of papyrus, matching the angle, and then made more copies, and formed them up into a circle: that's how I would do it. Still, here's the way the story is usually told, and how I told it in a book called 100 Discoveries, which is about how we probably discovered things.

Eratosthenes was a Greek astronomer, born in what is now Libya, and he died at Alexandria in Egypt. Being Greek back then was more of a cultural thing than a matter of living in Greece. If you spoke Greek, and especially if you were educated in the Greek way and lived among other Greeks, you were Greek, like Eratosthenes—or Archimedes, as we will see shortly.

Because he had access to the huge library in Alexandria, Eratosthenes learned about a vertical well at Syenê (today’s Aswân on the Nile). There, on a certain day of the year, the sun shone straight down the well at noon. And on the same day of the year, the noon sun was seven degrees and twelve minutes away from the vertical at Alexandria.

Divide 360° by 50, and you will see that 7° 12’ is one fiftieth of a circle so the two places are a fiftieth of the way around the globe. Long before Eratosthenes, the ancient Egyptians had noticed this difference in sun angle, but they thought the earth was flat, so they used the angular difference to estimate distance of the sun from the earth as about 5000 miles.

Eratosthenes knew the sun was much further off, which meant the sun’s rays must all be parallel, so the difference just had to be a result of the curved surface of the earth. Measure the distance from Syenê to Alexandria, multiply by 50, and there would be the circumference of the earth.

The angles were fairly accurate: modern Aswan is at 24° 5’ 23” north while Alexandria is at 31° 13’ north, so the angle was only wrong by about 1%, but the distance estimate was far more questionable. Syenê was not directly north of Alexandria, so they did not lie on the same meridian of longitude, meaning that if the measured distance was accurate, it would be too high. In any case, the estimated distance over land was always open to error.

The biggest snag for us is that Eratosthenes gave the distances in stadia. Back in the days when units were not standardized, this was fine. Sadly, the length varied from city to city and we have no idea exactly how long Eratosthenes took a stadion to be. If we assume the most probable length of the stadion, he was within a few percent of the correct measure of the planet—but he probably got close only because a few compensating errors evened out the rough bits in his method.

In the end, Eratosthenes said: “If the extent of the Atlantic Ocean were not an obstacle, we might easily pass by sea from Iberia to India, keeping in the same parallel.”

Then because we are in Egypt, I turn to Egyptian astronomy and the Nile floods. The Egyptians had no idea that monsoons in Ethiopia caused floods, but they knew when floods would come, based on the heliacal rising of Sirius, which is the time when Sirius is visible in the morning sky, just before the Sun, each August.

That leads me on to records in preliterate societies, and in the bush, not too far from the school, there are some petroglyphs, engravings in the rock made by Aborigines.

I have been seeking and photographing these for 60 years now, so I know a fair amount about them, as an uninitiated Gubba. I know that they were used for teaching, in much the way that I use PowerPoint. I also know that there are right and wrong ways to photograph them, and spilling water on them is now seen as the best way to record them.

Then there are the oral sources: it has been reported this year that the Gugu Badhun people of northern Queensland have a story about a pit with dust emerging and causing fire to run down gullies, and that sounds very like a volcanic eruption that probably happened 7000 years ago!

Working out some of the old stories mean they mean is hard, but some of them must have been reminders for things to do, or teaching legends, like Wirreenun the Rainmaker and Tiddalik the Frog.

(Wirreenun, in particular, has me excited, because it mentions using "ant-bed" [termite nest] to make a solid floor. I knew this as a common practice followed by early white settlers, but this points to their having obtained this from the people whose land they invaded.)

I will also mention a story from Jean A. Ellis's book, From the Dreamtime : Australian Aboriginal legends. This tale, The Two Brothers and the Pointers, explains the danger of fire, and whenever children looked up at the Pointers, two stars near our Southern Cross, they would be reminded to be wary of fire.

Here is a key point: I argue that the Greek legends about the stars are also using the stars as reminders, much the same as the way the original Australians used engravings and the stars — but the original Australians also used the stars as a calendar, just like the Egyptians, as these examples show:

Around Yirrkala, Orion and the Pleiades warn of storms that may upset canoes.
The Pitjantjatjara people lnew that the Pleiades (Kungkarungkara) in the dawn sky indicated the start of the dingo breeding (and hunting) season.
In Arnhem Land, the appearance of Arcturus and Vega was fish trap time.
In Victoria, that is time to look for the pupa of the wood ant.
Around Sydney, the Guringai were reminded when to gather emu eggs in October, by the Emu in the Sky.

Let's jump on this last one, because it relates to an engraving site that I have been visiting for 60 years: I went there first in 1957, but only now, have I found out Barnaby Norris' explanation. His pictures are copyright, and I am using them without permission, but I hope he will excuse my admiring use for educational purposes of one of those pictures. I got it from the link below, but go there for even better stuff.

There is a formation in the Milky Way, known in some Aboriginal cultures as the Emu. Here is Barnaby Norris' version of it:

Now the thing Norris noticed was that there are engravings of Baiame and his emu wife, on sandstone in Kuring-Gai Chase National Park, and in October, the Milky Way emu hovers above the stone one, just at the time when one should gather emu eggs.

In this way, the night sky became a reliable calendar (more reliable than the Julian calendar that was going haywire by the early 1500s when Copernicus began looking at it.

The Greeks had named the constellations and gave them legends that helped people remember them, but they named few stars, and they hardly used the stars for navigation, unlike Captain Bligh, who used something called plane sailing (and please notice the spelling!).

At this point, I launch into ways of making simple measures of angular distances in the sky, using hands, a cross stave and a simple astrolabe. I'll say more about those, some other time.

Then there's the kamal, invented by Arabic traders across the Indian Ocean. This uses a card and a strong with knots, and depending on the knot you use, can tell you if you are in the right latitude. The Arabs, by the way, gave a lot of stars their modern names: I cherry-picked this one from Wikipedia as well.

After a bit of jumping around, looking at early instruments, I come to the planets, and why they are called planets, heliocentric and geocentric models and the influence of printing and books and how, after Gutenberg invented moveable type in about 1460, there was a sudden surge in the 1540s: the titles, all in Latin, are left out here, but look up the author's name and the date if you want to know them.

1541, Paracelsus, medicine;
1542, Leonhard Fuchs, plant science;
1543, Vesalius, human anatomy;
1543, Copernicus, astronomy;
1544, Sebastian Münster, geography;
1546, Georgius Agricola, fossils.

One of those books, the De Revolutionibus Orbium Caelestium (see why I left the Latin out?) of Copernicus, proposed a new model for the solar system, but only to make it easier to correct the calendar that we had been using since the time of Julius Caesar.  he wasn't trying to change astronomy at all: if you think so, that's another Just So story.

Instead, I wrap up with a look at where the star watchers came from:

Aborigines;
Egyptians;
Babylonians;
Greeks;
Arabs.

I have to confess that I know little about any work done by the:

Chinese;
Indians;
Africans; and
Scots.

But I know a few individuals who deserve special credit:

Copernicus (Pole);
Galileo (Italian);
Brahe (Dane);
Kepler (German);
Newton (English).

The thing about science: there's no national science, just human science.

And that's quite enough moralising for one talk!