- TED Talks
TOEFL Quiz 11: The astrolabeQuiz #: 12234
Listening Comprehension from TED
Quiz by: Danielle_BIA
This transcript is copied from the Ted website.
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As technology progresses, and as it advances, many
of us assume that these advances make us more
intelligent, make us smarter and more connected to
the world. And what I'd like to argue is that
that's not necessarily the case, as progress is
simply a word for change, and with change you gain
something, but you also lose something.
And to really illustrate this point, what I'd like
to do is to show you how technology has dealt with
a very simple, a very common, an everyday
question. And that question is this. What time is
it? What time is it? If you glance at your iPhone,
it's so simple to tell the time. But, I'd like to
ask you, how would you tell the time if you didn't
have an iPhone? How would you tell the time, say,
600 years ago? How would you do it?
Well, the way you would do it is by using a device
that's called an astrolabe. So, an astrolabe is
relatively unknown in today's world. But, at the
time, in the 13th century, it was the gadget of
the day. It was the world's first popular
computer. And it was a device that, in fact, is a
model of the sky. So, the different parts of the
astrolabe, in this particular type, the rete
corresponds to the positions of the stars. The
plate corresponds to a coordinate system. And the
mater has some scales and puts it all together.
If you were an educated child, you would know how
to not only use the astrolabe, you would also know
how to make an astrolabe. And we know this because
the first treatise on the astrolabe, the first
technical manual in the English language, was
written by Geoffrey Chaucer. Yes, that Geoffrey
Chaucer, in 1391, to his little Lewis, his 11-
year-old son. And in this book, little Lewis would
know the big idea.
And the central idea that makes this computer work
is this thing called stereographic projection. And
basically, the concept is, how do you represent
the three-dimensional image of the night sky that
surrounds us onto a flat, portable, two-
dimensional surface. The idea is actually
relatively simple. Imagine that that Earth is at
the center of the universe, and surrounding it is
the sky projected onto a sphere. Each point on the
surface of the sphere is mapped through the bottom
pole, onto a flat surface, where it is then
So the North Star corresponds to the center of the
device. The ecliptic, which is the path of the
sun, moon, and planets correspond to an offset
circle. The bright stars correspond to little
daggers on the rete. And the altitude corresponds
to the plate system. Now, the real genius of the
astrolabe is not just the projection. The real
genius is that it brings together two coordinate
systems so they fit perfectly. There is the
position of the sun, moon and planets on the
movable rete. And then there is their location on
the sky as seen from a certain latitude on the
back plate. Okay?
So how would you use this device? Well, let me
first back up for a moment. This is an astrolabe.
Pretty impressive, isn't it? And so, this
astrolabe is on loan from us from the Oxford
School of -- Museum of History. And you can see
the different components. This is the mater, the
scales on the back. This is the rete. Okay. Do you
see that? That's the movable part of the sky. And
in the back you can see a spider web pattern. And
that spider web pattern corresponds to the local
coordinates in the sky. This is a rule device. And
on the back are some other devices, measuring
tools and scales, to be able to make some
You know, I've always wanted one of these. For my
thesis I actually built one of these out of paper.
And this one, this is a replica from a 15th-
century device. And it's worth probably about
three MacBook Pros. But a real one would cost
about as much as my house, and the house next to
it, and actually every house on the block, on both
sides of the street, maybe a school thrown in, and
some -- you know, a church. They are just
But let me show you how to work this device. So
let's go to step one. First thing that you do is
you select a star in the night sky, if you're
telling time at night. So, tonight, if it's clear
you'll be able to see the summer triangle. And
there is a bright star called Deneb. So let's
select Deneb. Second, is you measure the altitude
of Deneb. So, step two, I hold the device up, and
then I sight its altitude there so I can see it
clearly now. And then I measure its altitude. So,
it's about 26 degrees. You can't see it from over
there. Step three is identify the star on the
front of the device. Deneb is there. I can tell.
Step four is I then move the rete, move the sky,
so the altitude of the star corresponds to the
scale on the back. Okay, so when that happens
everything lines up. I have here a model of the
sky that corresponds to the real sky. Okay? So, it
is, in a sense, holding a model of the universe in
my hands. And then finally, I take a rule, and
move the rule to a date line which then tells me
the time here. Right. So, that's how the device is
So, I know what you're thinking: "That's a lot of
work, isn't it? Isn't it a ton of work to be able
to tell the time?" as you glance at your iPod to
just check out the time. But there is a difference
between the two, because with your iPod you can
tell -- or your iPhone, you can tell exactly what
the time is, with precision. The way little Lewis
would tell the time is by a picture of the sky. He
would know where things would fit in the sky. He
would not only know what time it was, he would
also know where the sun would rise, and how it
would move across the sky. He would know what time
the sun would rise, and what time it would set.
And he would know that for essentially every
celestial object in the heavens.
So, in computer graphics and computer user
interface design, there is a term called
affordances. So, affordances are the qualities of
an object that allow us to perform an action with
it. And what the astrolabe does is it allows us,
it affords us, to connect to the night sky, to
look up into the night sky and be much more -- to
see the visible and the invisible together. So,
that's just one use. Incredible, there is probably
350, 400 uses. In fact, there is a text, and that
has over a thousand uses of this first computer.
On the back there is scales and measurements for
terrestrial navigation. You can survey with it.
The city of Baghdad was surveyed with it. It can
be used for calculating mathematical equations of
all different types. And it would take a full
university course to illustrate it. Astrolabes
have an incredible history. They are over 2,000
years old. The concept of stereographic projection
originated in 330 B.C.
And the astrolabes come in many different sizes
and shapes and forms. There is portable ones.
There is large display ones. And I think what is
common to all astrolabes is that they are
beautiful works of art. There is a quality of
craftsmanship and precision that is just
astonishing and remarkable.
Astrolabes, like every technology, do evolve over
time. So, the earliest retes, for example, were
very simple and primitive. And advancing retes
became cultural emblems. This is one from Oxford.
And I find this one really extraordinary because
the rete pattern is completely symmetrical, and it
accurately maps a completely asymmetrical, or
random sky. How cool is that? This is just
So, would little Lewis have an astrolabe? Probably
not one made of brass. He would have one made out
of wood, or paper. And the vast majority of this
first computer was a portable device that you
could keep in the back of your pocket. So, what
does the astrolabe inspire? Well, I think the
first thing is that it reminds us just how
resourceful people were, our forebears were, years
and years ago. It's just an incredible device.
Every technology advances. Every technology is
transformed and moved by others. And what we gain
with a new technology, of course, is precision and
accuracy. But what we lose, I think, is an
accurate -- a felt sense of the sky, a sense of
context. Knowing the sky, knowing your
relationship with the sky, is the center of the
real answer to knowing what time it is.
So, it's -- I think astrolabes are just remarkable
devices. And so, what can you learn from these
devices? Well, primarily that there is a subtle
knowledge that we can connect with the world. And
astrolabes return us to this subtle sense of how
things all fit together, and also how we connect
to the world. Thanks very much. (Applause)
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