Bringing the Sky Down to Earth: Astronomy in Ancient Egypt




Uploaded by techEIU on 07.02.2012

Transcript:
♪ [music playing-- no dialogue] ♪♪
>> Dr. Allan Lanham: This series has
been going on for the last month,
and we're wrapping it today.
Dr. Linton is here in the afternoon, then we have one more
event today at 6 o'clock in McAfee Gym, if you would like to
experience sports and dancing from ancient Egypt.
We hope you will come, there will be live music,
dancers and athletes in addition to a lecture,
so we hope you'll join us there.
But I certainly thank you for all your patience
and expert listening over the several sessions here.
Our friend here has been to almost every one.
Did you miss one--I don't think so--yes, look at that.
So for 24 presentations--I think you deserve an award there.
I will leave you with Dr. Wafeek Wahby, who has expertly gathered
all our speakers for this series.
[audience applause]
>> Dr. Wafeek Wahby: Thank you, Dean Lanham
and thank you all for coming at this time.
At 3 o'clock on Wednesday, you could do something else in that
time slot, but thank you very much for coming, and this marks
the last day of this symposium, the ancient Egypt symposium
popularly known as "A Futuristic Look Through Ancient Lenses".
And it has been a joy to know more about this ancient
civilization that was one of the--it was the United States of
it's time, I think, and they left some things for us to get a
glimpse of their glory.
Well, stars are fascinating and have been fascinating to people
since the dawn of history.
Even at dawn, you can see some stars and you can mention, even
today, the word stars and you'll get millions of responses.
People like to be stars themselves.
Look at Hollywood if you like, or anywhere.
Everybody likes to be a star.
And one wise person said that we have--two days ago--
we have 7 billion stars, the population of the world.
Everybody thinks or likes to think that he is a star.
All the parents like to see their kids as stars.
So we have the 7 billion mark of world population two days ago,
if you like to know that information.
Now, to introduce sciences, stars and our distinguished
speaker, I am thankful for.
Dean would you please give us a hint of what you do in sciences.
My name is Godson Obia, I am the interim
dean of the College of Sciences, and I have missed most of the
presentations because of other engagements on campus, but this
one I made time to come to.
Dave Linton is my faculty member in physics and one of the
well-known professors on campus because of his expertise in
astronomy, am I right?
Okay, so today he's going to apply some of that science to an
understanding of ancient Egypt and Dave, good luck.
>> Dr. Wahby: Now, if you wish upon a
star, here it is.
>> Mr. David Linton: Thank you, thank you
both and thank you all for coming.
I would start off by saying I noticed all of the slides seem
to be shifted that way, so if you'll just
lean maybe it will help.
That's maybe an early indication that--you're going to miss a
little bit off the right edge and if that happens, hopefully I
can remember what it was because I can't see it
on my screen here either.
But the stars, the sky was extremely
important to the Egyptians.
Remember that this was a time when there was no light
pollution on this planet and this was a desert environment
and the skies were just gorgeous--must have been,
we can only imagine if we're here in Illinois
where it's not all that arid, fortunately, I guess.
And we do have some light pollution.
Now before I get going very far, I do want to,
I have three disclaimers.
One, if you're expecting a talk on astrology based on the
mistake that got into the paper yesterday,
you may want to leave now.
That, there is a difference between astrology and astronomy
and I wish to speak on astronomy.
Secondly, I'd have to say I'm not an expert on Egypt at all,
but I have significant interest in the history of astronomy,
as it bears on astronomy itself.
And thirdly, I've never been to Egypt, although it's on my
list--moreso now than when I started
reading up for this talk.
So I guess maybe the next slide to look at is this that was in
the paper yesterday, and I don't want to make fun of this--
it was as much my mistake, probably more my mistake
than anybody else's.
I wasn't careful about communicating over the phone, in
a phone interview, what I should've been alert to as a
very common misconception and confusion--astrology and
astronomy are not the same thing.
There's a lot of--I even missed the punchline in this cartoon,
now that's bad.
"I always get mixed up between astrology and astronomy.
Which is the stupid trivia one and which is the one you get
horoscopes in?"
But astronomy is a science--another one I will just
skip through here--astrology really a pseudo-science.
Really it's an ancient religion.
It was a religion at a time in a variety of parts of the world,
certainly in the Middle East when motions in the sky
were quite mysterious, it was trying to make a sense of life
and looking for correlation.
Certainly there were seasonal correlations to be found in the
heavens, timing of various things such as lunar phases and
seasons as well, with ripening of berries for example, or
patterns of game, and they looked further.
And they came to the conclusion or had the belief system that
where things were--where planets were, where the sun was
amongst the stars--would have a bearing on how,
what one's destiny might be and that sort of thing.
And the predictions of astrology cannot be tested, many of them,
with scientific methods and they don't stand up.
And at that point I guess you stop calling it an ancient
religion and say if you have a current belief in it,
you're having to do some mental gymnastics to get past the
evidence that says that where a star is, or where a planet is,
simply doesn't have any affect.
But as I read that article and then thought about it a
lot--because my initial reaction was just 'oh, my goodness'--
I realized, you know, it really is something that
maybe I should mention here.
Astronomy has matured, we've learned things, which is true in
any science or any discipline, I would hope, and at the time the
Egyptians , the time we're talking about within
ancient Egypt, astronomy was not what it is today.
We didn't have telescopes--a long way from it.
And astronomy and astrology were really one in the same.
The priests were looking at the stars, they were mapping them,
they were timing them, seeing when they set, when they
rose--same thing for the sun and the moon--planets,
where they were in certain constellations,
but also trying to give the king what he was requesting.
Whether this was a good year to go to war perhaps with the
neighboring countries.
So astronomy and astrology,
I'm sure I'm talking about both today.
Now I've never been to Egypt, but I have been to Africa
and I will say I have been to the Sahara Desert,
I've been on a camel.
My wife and I and two of our children,11 years ago for
semester break went to Morocco and we rode camels in
the Sahara Desert, on Christmas day no less,
and spent the night and I even, in the bazaar at Marrakech,
got to hold a cobra.
Check that one off--not going to do it again.
Saw a sign that said "Timbuktu--52 jours"
meaning 52 days, this way by camel, 52 days.
That was in the oasis that we encountered, that I had rented
the camels and we went out into the Sahara, so I seen a western
end, I haven't seen the eastern end of the Sahara.
Now the sky, this part of the sky, was one of the most special
parts of the sky for the Egyptians.
We know this is our winter sky.
These constellations are there in the
early evening in our winter.
You see Orion there--the two knees, the three stars in a row
for the belt, the two shoulders, the star that's red at the top,
one of the brightest stars in the sky.
Beetle juice is how it's usually mispronounced.
Betelgeuse is probably a little bit better.
The knee at the bottom is blue.
These are two stars that are decidedly
different in temperature.
Different in temperature--the cooler star and the warmer,
much hotter star, the blue one.
Over here the brightest star is seen from the Earth.
This is the star, Sirius, S-I-R-I-U-S.
And then, in the upper right, we have Taurus the bull.
We have the face of the bull--it's a
V-shaped face right here.
I'd jump up but probably would not be good for me.
Okay, V-shaped face, the star Aldeberan, the eye of the bull,
and over here Pleiades, also known as "the Seven Sisters".
Now if you look low in the left, you'll see a transitory
object--a meteor passing behind the trees got caught in this
photograph here.
Sirius is in the constellation of the dog, Canis Major--
that's the name it's given now.
To the Egyptians, Orion came to be associated with one of their
gods, Osiris, and Sirius came to be associated with Isis.
I think I've got some more slides here.
Yes, there's Orion.
Better view of it there.
Lot of faint stars, stars that you cannot see from here under
the lighting conditions that we have.
Here is a depiction from somewhere in Egypt at some
time--I don't know what the source of this is, but we have
Osiris being associated with what we now call the hunter, and
Isis, I'm sure that's what this must be.
Right here, remember, in fact you can see here the belt.
Remember from the previous slide that if you go down to the left
past the belt is pointing really to the star Sirius.
Sirius is a star that rises in our Southeast.
It doesn't get real high but it's very noticeable.
It is exceeded in brightness only by the sun and the moon and
by Venus and I think Jupiter at times is brighter than it is.
Jupiter's in our sky right now, in the east if you go out
anytime of the evening after the sun has
set--it will be there for you.
Venus, even brighter, is now entering the
western sky, but very early only.
Isis again, making a trek across the sky.
Now Sirius I'll talk more about, in fact, right here.
The flooding of the Nile River--that was vital to the
survival of the civilization, the survival of the individuals
in that civilization--most important annual event in Egypt.
Timing this, foretelling when it was going to happen, was a
really important task that was given over to the priesthood.
They found an astronomical association with this,
correlation, and that was with the rising of Sirius.
So what happens is as we go around the sun,
the stars that are behind the sun change.
It looks to us as though, if we could see the stars and the sun
at the same time--and that's tough, but you can imagine that
the sun, if I put something in the middle of this oval right
here and I walked around the table, it would look to me
as though that object in the middle was moving in front of
the background individuals here.
The sun seems to move through the stars.
Now, at a certain point in the year, it gets roughly in the
direction of Sirius--not exactly, but enough so that with
all that light, it's going to make Sirius impossible to see,
and then it goes past Sirius.
And if you're watching early in the morning, looking to the
east, before sunrise, the day will come when Sirius can be
seen rising just before the sun--it's separated itself
enough from the sun.
And it was at that time that the Nile was found to be flooding in
the capital city of Memphis--probably flooding
further south earlier.
Now 70 days--for that timespan Sirius cannot be seen due to its
proximity to the sun.
Seventy days.
What you can't see too well is this slide off to the
right--this is Osiris.
A green-skinned god.
A god that came to be associated with Orion and loosely with
Sirius as well, and remember these
constellations disappear for a while.
Remember that Osiris or--I haven't mentioned it,
but you may know--Osiris is the god of the underworld.
This is mythologically associated with the passage from
life, gone to the underworld, and this is one god from Egypt
religions that actually was resurrected, came back to life,
but life was now being placed in charge
of the underworld, the afterlife.
The calendar is associated very strongly with Sothis which was
one of the names that was used for Sirius.
Sothis or Sopdet, I believe.
Trying to pronounce some of the words, I forget.
But what they did was to start the year initially
with the flooding of the Nile.
It started with the rising of Sirius just before the sun.
They created a calendar that had twelve 30-day months in it.
The months were 30 days, the lunar cycle was 29 1/2 days for
the cycle of phases, so they were doing pretty much the same
thing we do today in terms of lengths of the months.
But that would just give you 360, they had
5 days of feasting at the end--not fasting, but feasting.
That "e" makes all the difference.
Three seasons of four months each.
The first season was the season of the flooding of the Nile, the
rise of the waters, the [unclear dialogue]
and the subsiding.
The next season was the season of cultivation
and the last season was the season of harvest.
Now the five day feasting was said to be unlucky for
any work to be done.
And we have a 365 day year--now, how long is our year?
Any astronomy students around?
Three hundred sixty-five and a quarter
is a whole lot better, yes.
So the day, the year is off by about six hours--365.2422 days,
that is, is the length of the year as we now understand it.
So if they had 365 days in it, they were about a quarter day
off, six hours, and so every four years they were going to be
a day out of sync--their calendar was, with the flooding
of the Nile if the Nile is that regular--and eventually any
variation that it had was swamped by the difference
between the calendar and the flooding.
This quarter day was adding up.
Over 1,460 years--the rising of the
Nile cycled through the seasons.
The priests knew about the quarter day discrepancy but they
didn't care--the calendar had been created.
Maybe they couldn't think of what to do, but they did notice
that the stars were better, a better predictor of the rising
of the Nile than their own calendar.
Fourteen hundred and sixty years.
I think it's a testament to the duration, the longevity of the
Egyptian civilization that they got to see this cycle through
their calendar twice after they created the calendar in about
3000 BC, I think.
I think that's about when it was put together.
Eventually, 46 BC, we have Julius Caesar modifying the
calendar by adding that February 29 every 4 years, but if you
paid attention to the news lately, it was in 1582, much
more recently, Pope Gregory VIII--that's 13 isn't it--XIII,
okay, he modified the calendar again because adding six hours
on the average, adding that one day
every four years is too much.
That would make it at 365.25 and really it's just slightly less,
so the century years are leap years only if they are divisible
by 400--2000 was a leap year, probably none of the rest of us
need to worry about any more of those, but come 2100 you can
warn your kids or grandkids it's going to be different.
I think I've mentioned all of this.
Yes, the rotation of the Earth is very
steady--just summarize it by that.
Now it's an interesting note that the priests were watching
the sky--I'm going to be focusing on one more thing that
they were doing especially--they're keeping
records, but there are certain things that they didn't notice.
Things that their neighbors to the east, the Babylonians, did,
over the course of several thousand years.
They noticed the Saros Cycle--18 years, 11 days, 8 hours.
Now this wasn't actually noticed by the Babylonians until
the reign of Nabû-Nasir, I believe it was, in the
Eighth century BC, where he really promoted science.
It was said by Claudius Ptolemy some thousand years later
almost--a little bit under that--that that was really the
beginning of real astronomy right there.
He asked his astronomers to pore through the records of old--
they had been keeping records, but now take a look at them,
see what you can find.
And what they found was that eclipses happen in cycles and,
for example, if you mark in your calendar August 21 of 2017,
head to Carbondale because that's going to be
on the center line of the next solar eclipse
in this part of the world and 18 years, 11 days later--
that would be 2035-- we have another one
and I believe it is this one right here.
I think that's it, but I think it is off the screen
in terms of the labeling.
Why is it in another part of the world?
Because of the extra 8 hours--the Earth gets another 8
hours to rotate, so that puts it further west by
a third of a rotation of the Earth.
And then in 2053, September 12--again advancing forward
11 days, although it may seem like only 10 in some cases,
it depends on how many leap years are in between these
particular dates as to whether the dates really
seem to be 11 days apart--but we're going to have another
one in the same cycle,
and this one actually passes apparently right through Egypt.
There are other cycles going on at the same time.
We don't have to wait 18 years between eclipses,
other cycles are happening as well.
They discovered this by looking at the data.
For example, if we go to 2024, we get to see another solar
eclipse and if you happen to be in Carbondale, you can just wait
for, from 2017 to 2024.
Just sit there and wait and you have the shadow of the moon
passing across you.
And others happen too, but this is just a different Saros Cycle.
Also, the Babylonians were paying attention to the planets
and discovering some things about the planets.
The planets for example, are changing directions.
This is Mars at probably about a one week interval, photographed
against fixed stars and obviously the stars
moving across the sky, but if you freeze those in your frame
or on your print, then Mars is a wanderer,
and that's really what planet means--wanderer.
They didn't know what the planets were,
they associated them with gods, goddesses.
Mars and Venus for example, the Roman names for god of war and
goddess of love, but this changing of direction like this
was really very difficult to explain and they worked on the
timings trying to understand that.
The Egyptians, though they were aware of these phenomena,
didn't pore into the data to find the cycles,
didn't seem to be that interested in this phenomena
neither and probably the reason was that it didn't correlate
with the flooding of the Nile at all.
That was survival.
When I talk about bringing astronomy down to Earth,
bringing the sky down to Earth, their focus was on survival,
focus was on that flooding of the Nile, keeping the king
happy--that's always a good idea.
By the way, up here you see the Pleiades
again--looks like a little dipper.
Anybody know what Pleiades means in Japanese?
Yes you do.
Some of you do.
Next time you see a Subaru vehicle,
look for the stars on it.
That's the emblem and that's what that means.
From the African continent, further south than Egypt,,
we get a glimpse, perhaps an idea, of what the skies of old
must have been like.
This is the Milky Way photographed from Botswana,
and the Southern Milky Way as well.
You have the dust lanes that lie between the stars, the dust from
dead stars--its buildup there--and dims the more distant
objects in the sky.
Really the dust lanes are the most,
the densest parts of the sky.
Take a look at this glyph, I would call it I guess
is general, from Egypt.
What you have here is the sky goddess and her name is spelled
N-U-T, and I believe it's pronounced nute,
and what does that look like to you?
Maybe I shouldn't ask it in such open terms, but I'm trying to
correlate it with the Mily Way arching overhead.
What you've got also is the earth god Geb, separated from
the heavens by the god of the air--he's holding up
and keeping the two apart.
Other things are in there and I don't think I'll go into those.
Another one that I would suggest to you is this one.
Many times you see the goddess Nut symbolized with star
representations along her body.
That's, same thing.
Okay, now let's turn our attention again in Africa and
look to the south.
And south point in the horizon, right below the
center of these circles.
This is a two hour exposure of the southern sky from south of
the equator and what you find is that the stars are rising in the
east--well, the ones that do at least.
This is the south, so east is over here, so some of the stars
out here are rising in the east, going around the pole--the point
that's overhead, the south pole of the Earth--and then setting
west of due south.
They're moving in clockwise circles.
They do a similar sort of thing in the northern hemisphere.
if you look toward Polaris, they are moving in circles but
they're moving again from east to west but now,
because you're looking in the opposite direction, it's
counter clockwise, and the stars within this circle are the stars
that would be circumpolar as seen from roughly Alexandria.
Alexandria is at a latitude of about 31 degrees,
we are closer to 40 degrees.
Consequently, the stars that are always overhead, always above
our horizon more correctly, are the stars that come right down
to the bottom of the screen.
The Big Dipper skims the northern horizon at it's lowest
point and gets up to an altitude, it's almost straight
overhead, about 80 degrees tops when it's highest in the sky.
The point Polaris, or right close to Polaris, is the point
amongst the stars that lies exactly overhead the North Pole
of the Earth, and as Earth rotates, we now understand,
the stars look like they're moving.
Really we're turning, but that turning, and along this axis,
makes that point seem motionless.
If you're at the North Pole pointing straight up
and the Earth turns, you keep pointing straight up to
the same spot amongst the stars.
That's less than a degree away from Polaris,
so that is our north star.
Okay, to the Egyptians, the northern stars
gave a permanence.
A sense of permanence, they're always there.
They're north of the hemis--north of the equator.
So their attention is going to be drawn much more to the
northern sky than to the southern sky
for any sense of that.
For the pharaohs, the belief arose that once they would die,
they would have a chance at immortality through being
transported to the northern sky, where you'd always be up there,
you'd become one of those stars--one of those 7 billions
stars--except at night you don't quite see 7 billion,
but there's a lot of them out there on a clear night.
Now we've got the two pointer stars that help us
in the Big Dipper, that help us to find Polaris.
The problem is that the pole star is wandering--not the pole
star, but the pole is wandering.
Why is it wandering, because the Earth is wobbling.
If you--and I think maybe I'll just look ahead here--if you
take a top and you spin it on the kitchen table or the kitchen
floor--some hard surface--spin it with it leaning, it's going
to spin, it's axis doesn't keep pointing in the same direction.
If you don't spin it, it falls over, but if you spin it you get
this precession right here.
The Earth is spinning like a top and it's not sitting on the
table, but gravity is pulling on it.
Gravitational pull of the sun and the moon are trying to
get it to fall over.
It's got an equatorial bulge, the equatorial diameter is about
70 kilometers more than the polar diameter.
Trying to get it to fall over,
but the spinning causes it to do this.
It takes 26 thousand years for the pole star to switch from
Polaris to Vega, and back to Polaris for example.
But we're looking at a time when the sky was a bit different.
We look back to 3000 BC and the north celestial pole, the point
directly overhead the North Pole of the Earth, was very close to
the star Thuban in Draco--I think
it's also known as Draconis.
Since then it has moved along.
Finally, we get to Polaris and about now, close to Polaris.
For the pharaohs, entombed in the pyramids or in other burial
sites, they had, according to their beliefs, they had to
prepare to go north.
So what priests did was to line up the buildings along
north-south axis, and of course the opposite sides, the adjacent
sides, would be east-west.
How do you that?
Well, the technique in about 2500 BC was to focus on the star
Kochab and the star down here at the bend of the handle of the
Big Dipper known as Mizar, M-I-Z-A-R,
because the pole was directly between these two points.
And this is 3000 BC but as you move along right here as the
pole does, it's right here, so they could find that, they knew
by watching during that time that that was due north,
but these two stars flanked the pole star perfectly--they're
equidistant--and they're kind of like, I use a phrase that's
actually applied to a couple of the other stars,
the guardians of the pole.
They were the guardians for the pharaohs really.
Aligned up for this.
What happens?
They keep doing this over time, this works perfectly
and I believe the year was 2467 BC, yes, 2467 BC, that
worked fine for finding north, but after a little bit of time,
a few years, a few centuries--there's plenty of
centuries to the Egyptians in that civilization.
The pole has wandered so instead of a point right in between
being motionless in the sky and marking the point directly over
the north point on the horizon.
If you find that point in the sky and line your building up
with it, this point over here is due north--maybe you've not
done your pharaoh any favors.
And so we can look at the buildings now and you can tell
when they were built by how much the sides deviate from the
north-south line because of this wandering.
So astronomy and archaeology have benefited from each other's
contributions., and that has now been dated, the great pyramid
has been dated by this method to have been constructed in
2480 BC, plus or minus 10 years based on
this alignment consideration.
Let's see, let's look in here.
This is a more detailed view of Kochab over here.
This is Beta Ursae Minor, second brightest star in that
constellation, and then we've got Mizar right in here--
it's actually two stars together, it's a binary star.
They're far enough apart that it's been a test of good vision
since at least the time of the Romans if you
could see them separated.
Right between this star and this star, you've got Thuban almost
right between it, but the pole was moving this way and I know I
turned the slide so I played around with doing this,
but I'm not real happy with that, for obvious reasons.
Trying to read it.
But each age seems to have its way to find the pole.
We have the means of finding the two stars in the Big Dipper and
drawing a line out of it--almost a perfectly straight line.
About five times the separation here lead you to Polaris.
It's not [unclear dialogue] bright star, but it is
motionless, it helps you find directions.
For a point about 400 to 500 years ago, find this star in the
bend of the handle of the Big Dipper, find this star--which is
the second brightest star, Ursa Minor--and half way in between
them you've got the point that once you drop your gaze straight
down to the horizon, you're looking due north.
One speculation, and I don't know enough to be convinced of
this yet--some claim it's true and some dispute that--is that
the three small pyramids here are representative
of the belt of Orion.
And certainly there is a connection between the
gods--you've got Osiris who's also
identified as the first pharaoh.
Whether that is a mythological characterization or not, I'm not
sure but certainly that was very important and perhaps that's
what this was supposed to represent.
Major buildings in Egypt were built to align
with stars or with the sun.
Here we have portions in this slide--and I think just one more
slide that I ended up including--from the temple of
Amun-Ra at Karnak.
Immense columns.
I, this morning, almost snatched up another picture of him on the
internet and put it on there, because it had some people in
the picture and it, I couldn't believe how tiny they were
compared to the height of these columns.
These columns are about 100 feet tall--just a little under it,
29 meters, you do the math.
They're tall.
This arrangement of pillars permits the rising sun to enter
only on one day of the year to the inner sanctum, and that day,
the first day of--well, that's curious that it's blacked out
because I had two sources that disagreed as to what day it was.
One was the first day of winter and the other source said the
first day of summer and I have not had my chance to track down
which that was, but the projector alignment has taken
care of that for me.
I'm not sure, but it was a significant day and it took some
engineering to get the pillars in just the right way or the
corners of doorways, the edges of doorways in just the right
position so that this shaft of light could make it down a very
long hallway to the sanctuary.
Not to be overlooked is the fact that they
did have these great clear skies.
And one thing that I would comment on actually from my
experience in Morocco--I went to Morocco with my family at the
time of Ramadan.
Ramadan ended quite coincidentally on Christmas day
that particular year.
And the Islamic calendar is a lunar calendar that also does
not synch with the seasons.
It's way out of synch compared to what the Egyptians had.
The Egyptians were off by 6 hours, this is out of synch by
well 29 1/2 days per month per lunar cycle times 12 months.
The months all start when they sight the
crescent moon in the evening.
Where do they sight it--in Cairo,
that's where the official place is.
That would be 354 days, so it's going to be about 11 and a
quarter days off every year, and now, what, 11 years after we
were there--that's close to 4 months earlier, and eventually
you get to the point where you're celebrating Ramadan not
in the winter time, but you're celebrating in the summer and
you're supposed to go, you're supposed to fast during
the daylight hours.
Well, that's a longer time come June than it is in December, and
it's much more of a challenge, but it doesn't matter, it's not
important to them, to the practitioners, the followers of
Islam, that the calendar be synched to the seasons.
They simply have, I imagine, in the modern day they would have
calendars that carry both dates--planners that have
both calendars, religious activities as well as
activities that conform to the calendar that the
modern business world was following.
I want to talk about one of the greatest achievements, perhaps,
by a scientist of more than 2000 years ago.
This was about 2200 BC, the man's name was Eratosthenes,
he was a librarian.
Here we are in the library, how can I pass up the opportunity to
talk about a librarian.
He was nicknamed Beta.
He said that he was second-best in the world in everything.
He was a cartographer, he was a mathematician,
he was really good but wasn't tops in any field.
But his job was to acquire information and one day from far
up the Nile--and that's where the modern high dam, Aswan is,
those of you who were here, that's where it is.
Syene was the name of the little town there.
Out came a report to Alexandria that the sun was straight
overhead at noon on the first day of summer.
Sunlight went all the way to the bottom of the wells,
the tall poles cast no shadows.
Now the idea was already established
that the world was round.
If you've heard, as many of us were taught, that Columbus set
sail at a time when the populus understood the world to be flat,
that's a flat out falsehood--that ain't so.
This was established long before that.
Aristotle, 150 years before Eratosthenes had taken the
reports of travelers who had gone to the north and said 'hey,
the north star is higher' and those who had gone to the south
and said 'hey, the north star is lower' and said oh, the Earth
must be round--and he wrote that and Aristotle's word was taken
as the authority in science.
Eratosthenes, when he reads this, says--I don't know what he
said for sure, but I really imagine that he checked the sky,
the sun on the first day of summer in Alexandria,
and he did not find that it was straight overhead.
Now in a flat Earth, if it's straight overhead Syene,
it's going to be straight overhead in Alexandria,
but on curved Earth it can go down the well there and cause
the poles here to cast shadows.
And he didn't stop there.
He thought about it, realized that he had a means here of
going further.
If he could measure the, how far an angle the sun was away from
being straight overhead, the Zenith.
If he measured that difference he would have the same angle
that these two lines, vertical lines would intercept at the
center of the Earth.
And it turns out to be just the difference in latitude--7.2
degrees approximately.
So he measured the shadow angle, the deviation from the state
overhead, and then what else does he need to go further?
Well what's he after?
He's got this distance, and he's got the
whole distance around the Earth.
This angle right here is 7.2 degrees, what's the entire
angle, it's 360.
Whole distance around the Earth, certainly I don't know that if
I'm living in Egypt 4500 years, well, 2200 years ago.
But maybe I don't even know how far it is to Syene.
Several stories come about here, one of them that he paid for
survey to be conducted, paid for someone who was a pacer and a
counter to hike the distance which was 5000 stadia.
This was the distance unit used by the Greeks at the time.
About 5000 stadia, and 7.2 degrees is exactly 1/50 of a
complete circular angle so he was looking at that distance.
If you can measure it to be--
that equation's wrong, isn't it?
Not 1/50 times S, but S divided by 1/50.
Fifty times S.
Take the distance S and multiply it by 50.
How embarrassing, I got one of my equations wrong.
And how close did he come?
The value that he found was about 45,000, maybe closer to
45,500 kilometers in modern units.
The accepted value today is a little bit over 40,000
kilometers--about 40,080 around the equator, 40,075.
But I put a question mark and an asterisk over on the right there
because there is doubt about transferring, converting his
units of stadia to kilometers because the stadion as a unit of
length was the length of the Olympic stadium and by this
point in time there had been several, and they weren't all
the same length, so his worst results are right here.
This is as far off as he could've been apparently.
If you give him credit for the, using the stadion that would've
given him the best results, he was off by maybe 1 percent.
In any case, how much of the world is known in Egypt, or in
Greece or in the Mediterranean at that time?
It's the Mediterranean, it's maybe as far as Babylonia, and
then beyond, maybe touching India a little bit, and maybe
there's a sense of just how little of the world they know
when they can see the size of the world there.
When Columbus goes before the College of Sciences, prior to
1492, to argue his case for being given a grant to
sail westward to India and Japan, they said 'you're out of
your mind, look how big the world is, look how far that is.
'You can't carry enough provisions to get there'.
He tried other arguments but this measurement was cited,
this measurement had been reproduced in many ways
and the size of the world was known, as well as its shape.
I leave you here with one more look at the Milky Way from
a very dark location.
I think it's a beautiful view, and we have gained greatly in
our modern society from--and certainly in our science of
astronomy--from the dark, clear skies of the Middle East.
I thank you very much for coming.
[audience applause]
>> Dr. Wahby: Thank you.
Any questions?
This microphone is not for sound but for taping, so if you have a
question, I'll give you this to tape it.
Questions about stars.
I have a question, just general one--when you see all these dots
in the sky, why is it that people say connect this and this
and this and make this shape, not this and this
and make the other shape?
>> Mr. Linton: That's a very good question.
Your eyes tend to be drawn to the brighter stars and I will
offer a supposition, not a certain answer, but if you have,
in your culture, some stories to tell and those stories are about
heroes and villains, and you're sitting around the camp fire and
telling that story, you probably don't have an easel and a marker
to draw it out but you can get creative with dots that are just
up there in many different places, and you can maybe find
some creative ways to illustrate your story.
And then that gets handed down around the camp fire
and on to an age when maybe it's written down.
>> Dr. Wahby: And became time-honored
or something.
Any other questions?
Wish upon a star.
Okay, since we have no questions,
that means we have all the answers.
[audience applause]
>> Mr. Linton: Thank you
[no dialogue]