Ancient Astronomy: Babylon

SO before making this video I knew
that Greek astronomy was, to put it kindly, “inspired” by Babylonian astronomy.
But I didn’t realise how much of an influence it had on modern astronomy. Really a lot of concepts and research techniques that are still used today
were developed in ancient Babylon. But the first thing we really need to get
out of the way is the fact that in ancient cultures astronomy and astrology
were not separate things like they are in the modern era. The reason for
this being that being born so long before even the telescope was invented
there were really only a handful of reasons that somebody would actually
want to track the night sky. Those mainly being: navigation, the
creation of calendars, and to track omens. And Babylonians actually kind of did
omens backwards to how everyone else did. So instead of observing an omen,
deciding what was going to happen based on the omen; they would write down what
they had observed say if there had been a meteor shower or something, and then
they would look later on at things that had happened afterwards and come back to their
initial observation and say what it had been a prediction for. And in doing
this they were able over time to develop the ability to predict beforehand easily
predictable events. And they stored these in a special kind of – not a book because
they were tablets – but like a book called the Enuma Anu Enlil and kind
of… one of the big ones was eclipses. Because they occurred really regularly,
and were one of the easier things to predict. And the big reason that they
actually wanted to make these predictions in the first place is
because it was a fundamental belief of the culture that astronomical
events were actually intentionally put there by the gods to be observed by
humans, so they could predict the future. So certain things ended up having a
certain specific interpretations associated with them over time. An eclipse was associated with the Gods being angry with the king; so what
they would do is whenever they knew that an eclipse was coming they would
switch out the king with a fake king, and they would put that King just on the throne for
that day, and they would make a nice self-fulfilling prophecy by ending the
ceremony with killing the fake king. And we do actually have a lot of the
documents that they kept, which we’re going to come back to, but in terms of
how astronomers were actually implemented into society we really only
have Greek records remaining, we don’t have any sort of first hand Babylonian
accounts. So Strabo of Amasia writes about the Babylonian astronomers: So Strabo tells us that
the Chaldeans, which was just the Greek name for these astronomers, all
studied more or less the same thing, but there’s a bit of variation depending on
which city they lived in, and as evidenced by the fact that he talks
about the importance of their research to mathematicians; there is a lot of
maths involved in what they’re doing. They recorded their research down and
three different types of documents: star catalogues, astronomical diaries, and almanacs.
So the star catalogues are the bit that varies by location: because different
city-states put importance on different sets of stars. And so those stars could
be used for predicting omens within that city-state, but they wouldn’t
have those associations within a different city-state. The astronomical
diaries are really the bread and butter of the work of the Chaldeans.
They’re pretty much exactly what they sound like: every single night
they go out and make observations about the night sky they, record down the
positions of the moon and of the planets, and they report any noteworthy events
that they observed so eclipses, obviously, very important… meteor showers, anything that was out of
the ordinary and then they were to keep that information written down they would
wait to see what events occurred and then they would come back and they would
determine what things were associated with those events. But then we kind of
have the flip side of what they were doing with all their research and
gathering it up because idea together and making into almanacs
which was to create calendars. As you might be aware creating calendars
was very difficult for every single ancient society because there’s kind of
this need to manage the year by the Earth’s position around the Sun, because
that governs the seasons (and that’s kind of the major thing that they want to
track) so that they can keep track of when harvests happen, and things like that.
But a year obviously is a very long chunk of time, and there’s a need to break
it down. And pretty much everyone goes for breaking it down with lunar months.
But lunar months don’t even come close to fitting in perfectly into years. Which
is why and the modern Gregorian calendar months are just
standardised sets of time that don’t change. And it’s just every year; this
month is this number of days, and it doesn’t change (except for when we have a
leap year). Because your choices are: basically to have a really complex
system or to do that. And not include the moon in your months at all.
But what the Calvin’s managed to actually figure out with all their
gathering the research ,and doing all their maths, and building this kind of
profile of how everything works is that’s the difference between 235 months and 19 years was just 2 hours, and
that sounds great, right? Because that means that every 12 sets of 19 years – or
every 228 years – you gain an extra 24 hours so you have an extra day and that should
be it, right? Every 228 years a leapday. But it doesn’t really work like that.
Our Gregorian calendar can work like that because it’s basically set up so
that a cycle of years and a year are the same length of time, but because the
cycle of years for the Babylonians was 19 years that meant that every 19 years
the start of the year would be on the same day, but for the years in between
it would move around. So they had to conduct a complex system of adding in
months on specific years within the cycle, so that they could adjust the
position of New Year’s Day to be as close as possible to the spring equinox.
And they did actually update this sometime in the 4th century BC. They
came up with a better system that was 76 years long, and the start of year moved
around a lot less in it and it was obviously a lot easier for them to
manage. And this calendar was so advanced, and so accurate for its time that it
ended up spreading to other cultures: as you recall from what Strabo said the
Chaldeans were spread out but they weren’t just in the heart of Babylon – they were
with Arabic people and other people. So even actually the modern Hebrew calendar
is still based on this ancient Babylonian calendar. On top of having a
cycle for years, they actually also had a cycle for eclipses, because they managed
to figure out from all the gathering of data that there’s actually a
specific pattern that eclipses followed. That repeats every 18 years and
11.3 days, so they were able to quite easily track this because
they would just move along the cycle and see where they were so they always knew
if an eclipse was coming up. And the cycle actually worked for both lunar and
solar eclipses. And as you probably figured out at this point they were very
good at tracking the lunar month, but they were also good at tracking what’s called
an anomalistic month. which if you think about how the Moon cycles
around the Earth it travels along an ellipse, and it’s closest to the earth at
one point. And and an an-om-a-list-ic cycle is the time it takes for the Moon
to…from its closest point travel along the ellipse and then come back to that
closest point again. And they originally had a system for this (system A) where they mapped
out the speed that the Moon was travelling at by just using 2 speeds to
approximate the Moon; so when it was travelling along the kind of longer paths
of the ellipse it would be travelling at the highest speed, and when it was kind
of travelling along the little curved paths at each end it would be travelling
at the slowest speed. And at some time and the late 5th century they replaced
this with system B where the speed of them would change as a function of
the time so it would change like a sinusoidal wave. This is really
impressive and it really speaks volumes for the quality, and the accuracy of the
measurements they were taking because the size of the Moon in the night sky only
changes by about 11%. What’s more they actually also developed the
notation measuring out a circle by dividing it into 360 degrees, and
having 60 minutes of arc between each degree. And this is obviously still used
to this very day by astronomers to map out the position all the stars, and other
objects in the night sky, And obviously 360 degrees is still the system that
we most commonly use for measuring out circles. So that’s really you know an
understatement to say that without the Chaldeans, and their research, and
development that they made science really wouldn’t be the same at all.
I hope you enjoyed this video I personally enjoyed making it. I have
plans to make a more of these about other ancient cultures and their astronomy. Next week I’m gonna be
returning back to a regular astrophysics video, but as usual at the meantime I do
have like this in the description below if you would like to read more about the
Chaldeans and how they worked, and of course feel free to ask any questions
you might have in the comments below, and I’ll be seeing you next week. Bye!

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