OFFICIAL23 What is the lecture mainly about?

[00:00.00]NARRATOR: Listen to part of a lecture in an archaeology class.
[00:05.63]FEMALE PROFESSOR: I was talking to one of my colleagues in the physics department the other day, and we ended up discussing how one discovery can change everything. [00:14.47]My colleague mentioned how the theory of relativity completely changed the field of physics.
[00:20.27]At any rate, that conversation got me thinking about archaeological finds that really changed our understanding of ancient civilizations, [00:28.67] so I want to talk about the discovery of the Antikythera Mechanism.[00:33.29]The Antikythera Mechanism was found a hundred years ago, underwater in an ancient Greek shipwreck in the Mediterranean Sea. [00:41.99]It was in extremely poor condition and in many corroded pieces—[00:46.90] but once we figured out what it was and reconstructed it, [00:50.82]well, I simply don't have the words to convey how extraordinary this find was.[00:56.20]The Antikythera Mechanism is a relatively small device—roughly the size of a shoebox—made of gears fitted inside a wooden case. [01:06.50] In its original state, there were rotating dials and other indicators on the top with letters and drawings showing the Sun, the phases of the Moon, and different constellations. [01:18.90] Inside the box bronze gears would've rotated the displays.
[01:23.46]The displays—uh, the indicators of the Antikythera Mechanism would then move to show the motion of the Sun and the Moon relative to the planets and stars. [01:34.07] The device could be used to tell the different phases of the Moon and much more.[01:38.80]Well, scientists have recently analyzed the inscriptions on the mechanism and[01:56.64]What makes that so fascinating is that before we found the Antikythera Mechanism, the earliest device we had that could track the Sun and Moon like this was invented over a thousand years later! [02:09.75]So when this was first found, people literally would not believe it. [02:14.33]Some of my colleagues insisted it had to have been made well after 100 B.C.E., but the physical evidence was conclusive—it was that old.
[02:25.03]Of course, part of what made this find so unusual is that the Antikythera Mechanism is constructed of bronze. [02:32.85]It's not that bronze was all that rare in Greece then—it's just that bronze was valuable and could easily be recycled. [02:40.88]It would have been relatively easy for a person with knowledge of metals to melt down bronze objects and forge them into, [02:48.30]oh, say, coins—[02:50.13]bronze was used to make money back then—[02:52.64]or mold the bronze into anything else of value, for that matter.
[02:57.00]We're very fortunate that the device ended up underwater—because otherwise it probably would have ended up recycled into [03:04.23]who-knows-what.[03:05.67]Now, it was a challenge to figure out the Antikythera Mechanism?[03:10.00]it spent over two thousand years at the bottom of the sea before it was discovered,
[03:14.93]and even after it was discovered, it was still a number of years before we really understood what it was. [03:21.38]You see, the mechanism had corroded under water and many of the gears were stuck together in a mass. [03:28.70] Cleaning it was only partly successful. [03:31.40]We could only get a good look at the structure of the gears after gamma rays were used to see inside?mm, very similar to the way X-rays are used to see your bones.
[03:42.27]Now, once we got a look inside, we saw a really complex device. [03:47.78]The many gears not only moved in a way that could indicate the phases of the Moon, [03:52.70]the Antikythera Mechanism also tracked both the lunar year and the solar year. [03:58.56]Additionally, the gears also moved to match the motions of the planets and predicted eclipses! [04:05.33]But one thing that is particularly notable is that the mechanism was so precise that it even took into account a particular irregularity in the Moon's orbit—which requires some very complex math to replicate in a mechanical device.
[04:22.59]You could say that the Antikythera Mechanism was a very precise calendar. Which stands to reason—calendars were very important to ancient peoples. [04:33.40] Religious festivals had to be held at the right time of year, crops needed to be planted at the right time as well, [04:39.77] and let's not forget that eclipses and planetary motions had important symbolic meanings.