From realizing the truth about orbits, to
understanding the size of the moon, and more!
Join me as I reveal to you amazing astronomical
discoveries from ancient Greece!
You might think it odd that we're focusing
solely on a certain culture in regards to
ancient astronomy because as we all know there
were MANY nations that went and did various
forms of astronomy themselves.
Including the Babylonians, the Chinese, and
more.
But the Greeks were ones who helped figure
out certain things over time and put certain
standards in place that would allow us to
be where we are today.
For example, the name "planet" comes from
the Greek term "planētēs", meaning "wanderer",
as ancient astronomers noted how certain lights
moved across the sky in relation to the other
stars.
Five extraterrestrial planets can be seen
with the naked eye: Mercury, Venus, Mars,
Jupiter, and Saturn, the Greek names being
Hermes, Aphrodite, Ares, Zeus and Cronus.
S
ometimes the luminaries, the Sun and Moon,
are added to the list of naked eye planets
to make a total of seven.
Since the planets disappear from time to time
when they approach the Sun, careful attention
is required to identify all five.
Observations of Venus are not straightforward.
Early Greeks thought that the evening and
morning appearances of Venus represented two
different objects, calling it Hesperus ("evening
star") when it appeared in the western evening
sky and Phosphorus ("light-bringer") when
it appeared in the eastern morning sky.
They eventually came to recognize that both
objects were the same planet.
Pythagoras is given credit for this realization.
In classical Greece, astronomy was a branch
of mathematics; astronomers sought to create
geometrical models that could imitate the
appearances of celestial motions.
This tradition began with the Pythagoreans,
who placed astronomy among the four mathematical
arts (along with arithmetic, geometry, and
music).
The study of these four arts was taken upon
by many, including Plato who used it as part
of his own philosophical teachings, and even
advised some of his students to do the same.
According to a story reported by Simplicius
of Cilicia (6th century), Plato posed a question
for the Greek mathematicians of his day: "By
the assumption of what uniform and orderly
motions can the apparent motions of the planets
be accounted for?"
(quoted in Lloyd 1970, p. 84).
Plato proposed that the seemingly chaotic
wandering motions of the planets could be
explained by combinations of uniform circular
motions centered on a spherical Earth, apparently
a novel idea in the 4th century.
The problem though was that many of their
ideas and notions about how the solar system
worked as a whole still was flawed.
One of which was the Eudoxan System, which
was considered great by some, but not by others
because it was flawed in terms of being accurate.
In the 2nd century BC, Hipparchus, aware of
the extraordinary accuracy with which Babylonian
astronomers could predict the planets' motions,
insisted that Greek astronomers achieve similar
levels of accuracy.
Somehow he had access to Babylonian observations
or predictions, and used them to create better
geometrical models.
For the Sun, he used a simple eccentric model,
based on observations of the equinoxes, which
explained both changes in the speed of the
Sun and differences in the lengths of the
seasons.
For the Moon, he used a deferent and epicycle
model.
He could not create accurate models for the
remaining planets, and criticized other Greek
astronomers for creating inaccurate models.
Hipparchus also compiled a star catalogue.
According to Pliny the Elder, he observed
a nova (new star).
So that later generations could tell whether
other stars came to be, perished, moved, or
changed in brightness, he recorded the position
and brightness of the stars.
Ptolemy mentioned the catalogue in connection
with Hipparchus' discovery of precession.
(Precession of the equinoxes is a slow motion
of the place of the equinoxes through the
zodiac, caused by the shifting of the Earth's
axis).
Hipparchus thought it was caused by the motion
of the sphere of fixed stars.
Still though, their thoughts on the solar
system at large were wrong, and for a very
basic reason, they didn't really understand
what was at the center of the solar system.
In the 3rd century BC, Aristarchus of Samos
proposed an alternate cosmology (arrangement
of the universe): a heliocentric model of
the Solar System, placing the Sun, not the
Earth, at the center of the known universe
(hence he is sometimes known as the "Greek
Copernicus").
His astronomical ideas were not well-received,
however, and only a few brief references to
them are preserved.
We know the name of one follower of Aristarchus:
Seleucus of Seleucia.
Aristarchus also wrote a book On the Sizes
and Distances of the Sun and Moon, which is
his only work to have survived.
In this work, he calculated the sizes of the
Sun and Moon, as well as their distances from
the Earth in Earth radii.
Shortly afterwards, Eratosthenes calculated
the size of the Earth, providing a value for
the Earth radii which could be plugged into
Aristarchus' calculations.
Hipparchus wrote another book On the Sizes
and Distances of the Sun and Moon, which has
not survived.
Both Aristarchus and Hipparchus drastically
underestimated the distance of the Sun from
the Earth.
Nevertheless it is a jawdropping finding,
especially when you consider that it wasn’t
rediscovered until the 16th century, by Nicolaus
Copernicus, who even acknowledged Aristarchus
during the development of his own work.
Think about that, we could've have a much
greater understanding of the universe if the
Ancient Greeks believed in Aristarchus and
his findings.
But, not unlike many events that would happen
between and after the time of Copernicus,
anyone who didn't have a certain viewpoint
of the universe (meaning that it was the "center"
of the universe and that it was the plan of
the gods to make it that way) were put on
blast.
Because it didn't 'conform' to the larger
will and beliefs of the Greeks.
The irony of this is rich, obviously.
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So EVENTUALLY they realized that the sun was
the center of the solar system, but what else
did they figure out?
Well, remember what I said about the two astronomers
Aristarchus and Seleucus trying to figure
out the size of the sun and moon?
Well it's a lot more complicated in figuring
that out than you might think.
At the instant when the Moon is at first or
third quarter, Aristarchus reasoned that the
Sun, Earth, and Moon would form a right-angled
triangle.
As Pythagoras had determined how the lengths
of triangle’s sides were related a couple
of centuries earlier, Aristarchus used the
triangle to estimate that the distance to
the Sun was between 18 and 20 times the distance
to the Moon.
He also estimated that the size of the Moon
was approximately one-third that of Earth,
based on careful timing of lunar eclipses.
Obviously he was wrong about the sun as we
noted earlier, but the moon bit wasn't too
far off.
To be technical, the size of the moon compared
to the Earth is just over a fourth.
Or .27 the size of Earth.
But given that that's only about .06 off from
what he noted, that's still a pretty accurate
guess given all that he had to work with.
This is one of the reasons why it's so incredible
that astronomers like Aristarchus was able
to do at least somewhat accurate interpretations
of the solar system and the universe as a
whole in some cases hundreds of years before
anything SHOULD'VE been noted accurately.
And yet, they did it, and while not everything
was right, a lot of things hit the nail on
the head, or was pretty close.
Much of what the Greeks did set a tone or
a standard (or learned to be a standard) so
that others could take up what they learned
and adjust, get better, and more.
And that wasn't the only thing that the Greeks
basically got right, they also made some correct
predictions about the Earth itself which was
pretty spectacular at the time of its learning.
Eratosthenes (276BC to 195 BC) was chief librarian
at the Great Library of Alexandria, and a
keen experimentalist.
Among his many achievements was the earliest
known calculation of the circumference of
the Earth.
Which you might not think of as something
that would be Earth-shattering if you will,
but in fact it was a key thing to determine.
Pythagoras is generally regarded as the earliest
proponent of a spherical Earth, although apparently
not its size.
Eratosthenes’ famous and yet simple method
relied on measuring the different lengths
of shadows cast by poles stuck vertically
into the ground, at midday on the summer solstice,
at different latitudes.
The Sun is sufficiently far away that, wherever
its rays arrive at Earth, they are effectively
parallel, as had previously been shown by
Aristarchus.
So the difference in the shadows demonstrated
how much the Earth’s surface curved.
Eratosthenes used this to estimate the Earth’s
circumference as approximately 40,000km.
This is within a couple of percent of the
actual value, as established by modern geodesy
(the science of the Earth’s shape).
Later, another scientist called Posidonius
(135BC to 51BC) used a slightly different
method and arrived at almost exactly the same
answer.
Posidonius lived on the island of Rhodes for
much of his life.
There he observed the bright star Canopus
would lie very close to the horizon.
However, when in Alexandria, in Egypt, he
noted Canopus would ascend to some 7.5 degrees
above the horizon.
Given that 7.5 degrees is 1/48th of a circle,
he multiplied the distance from Rhodes to
Alexandria by 48, and arrived at a value also
of approximately 40,000km.
Do you want to know the exact circumference
of the Earth?
That would be 40,075 km.
Yep, they were just 75 kilometers off the
exact size.
And they did this LONG before it should've
been done.
All they did was use basic science and the
various tools and math that they had available
to them, and they made it work.
Just goes to show you that sometimes the most
complicated of things can be figured out using
the basics.
Of course, the Greeks weren't above making
complicated things as well.
Let me ask you a question, do you know what
the Antikythera Mechanism is?
The amazing device was discovered in an ancient
shipwreck off the Greek island of Antikythera
in 1900, and it is in fact the worlds' oldest
mechanical calculator.
If you were to look at it now, you wouldn't
be impressed by it, that's what happens when
you're underwater for many, many years.
But once upon a time it would've been one
of the most advanced and complicated devices
in all the world, and it had a very special
function, to help people understand where
everything was in the sky based on the date.
When manually rotated by a handle, the gears
span dials on the exterior showing the phases
of the Moon, the timing of lunar eclipses,
and the positions of the five planets then
known (Mercury, Venus, Mars, Jupiter, and
Saturn) at different times of the year.
This even accounted for their retrograde motion
– an illusionary change in the movement
of planets through the sky.
Think about that for a moment.
Think about how one had to know an extreme
amount of things about the solar system and
how everything worked to get this device to
happen.
Then, I want you think about how it was very
likely this device was made all the way back
in the 3rd or 1st centuries BC.
Exactly, someone made this thousands of years
before they reasonably should've.
Examiners of the device noted that something
of this caliber, of this machination was not
found for another thousand years.
So for the Greeks to make it, and be accurate
about it?
That was quite a feat of engineering.
Though no fully intact Antikythera Mechanism
has been found, that doesn't mean we can't
learn from it, and many are studying to try
and figure out more about how it worked.
As well as any clues as to who made it.
The prevailing theory is Archimedes, but that's
just that, a theory.
It also should be noted that aside from the
discoveries we listed here, that Greek Astronomy
had a major impact on other parts of the world,
including helping inspire the people of India
to take it up themselves and learn from their
models.
And it's more than fair to say that the full
extent of the reach and understanding of the
Greeks and their dives into astronomy will
never be known.
Mainly because many texts and book (some outlined
earlier) have been lost to time or were destroyed
because of their contents and views.
But that's not to say that their impact isn't
felt to this day.
In fact, for many centuries and millennia
to come the Greeks influence on astronomy
is felt.
From the naming of planets and stars after
their pantheons, to the constellations having
various connects to Greek mythology, and more.
Today, astronomy and the exploration of space
is one of the most important things in the
world, including the act of trying to get
us onto other planets.
But imagine how far behind we would be if
the ancient cultures like Greece didn't go
and start everything off all those centuries
ago...
Thanks for watching everyone!
What did you think of this look at Greek Astronomy
and how they helped discover or understand
various parts of the solar system?
Which of these discoveries were you most surprised
about in terms of their finding?
Can you believe how good or accurate the Greeks
were in some of their analysis?
Let us know in the comments below, be sure
to subscribe, and I'll see you next time on
the channel!
