A solar eclipse occurs when the moon passes between the sun and the earth. However the moon can also eclipse a star which is called a lunar occulation. These can be used to measure the size of a large star. When a bright star passes behind the moon astronomers can measure the time it takes the moon to start to cover the star to the moment when the star is completely eclipsed. This time will be a small fraction of a second but with knowing how fast the moon is moving it is enough to calculate the size of the star.

(The Great Courses – The Life and Death of Stars)

People nowadays use the terms vellum and parchment interchangeably to describe medieval writing surfaces but in fact it appears that vellum was from calves and parchment was from goats. After the skins were processed for writing and laid out for a book there was an attempt to make the pages appear uniform so the skin side was always facing the skin side of the opposite page and the same for the non-skin side. In some books you can still see where hair was removed and some scribes would complain about those poorly processed pages and how difficult it made their job of writing.

(The Great Courses – The Medieval World)

The light detectors in telescopes record light in a linear fashion. That means that if the light is twice as bright it will appear as twice as bright in the detector. This is not how light is detected in our eyes. Light detection in our eyes is recorded in a logarithmic way. If a light appears to be 5 times as bright it is in fact 100 times as bright. This allows us to visualize a large variety of brightness in objects.

(The Great Courses – The Life and Death of Stars)

How can we tell the temperature of a distant star? it turns out that there is a relationship between the color of a star and it’s temperature that is called Wien’s law. The wavelength of light at which a star most strongly emits is inversely proportional to the temperature.

(The Great Courses – The Life and Death of Stars)

In ancient Rome it was believed that important events happened for every man at each seventh year of his life up to his sixty third year. The celebration of the third of these cycles is one of the reasons for the importance placed in modern world on the 21st birthday.

(Book – Hadrian and the Triumph of Rome – Anthony Everitt)

The first Gothic Cathedral was the church of Saint-Denis which was built in 1140 CE. The Gothic Cathedral was not a matter of new building techniques, just a matter of combining already existing techniques in new ways. The difference between a Cathedral and other churches is that the ‘seat of a bishop’ is in a Cathedral.

(The Great Courses – The Medieval World)

Many maps in the Middle Ages showed East at the top of the map instead of North and Jerusalem was in the center since it was the goal of many people to make a pilgrimage there.
(The Great Courses – The Medieval World)

Weather cycles bring El Nino events in the Pacific along the coast of Peru. These can occur every few decades but also super large events can occur every few hundred years. These can bring warm water that kills fish and they can bring floods and droughts along the coast and even inland. It appears that these events destroyed many cities in at various times in the past. The Moche (800 CE) and Chimu (1000 CE) civilizations had cities that were destroyed. There was also a large event in 1100 CE that appears to have destroyed cities of the Sican who were known as the goldsmiths of the north coast.

(The Great Courses – Lost Worlds of South America)

In the Middle Ages millers had a very bad reputation like the one portrayed by Chaucer in ‘The Canterbury Tales’. They made their living by grinding grain and taking part of it that was called the ‘soke’. They got their bad reputation from taking more than their fair share and this is how we got the current term called ‘getting soaked’.
(The Great Courses – The Medieval World)

Traditional western views of the Amazon says that large civilizations could not exist there and since the people in this region had perishable building items instead of stone it is hard to find evidence of these civilizations. In recent decades there is evidence that there were large numbers of people who lived in this area. Large mounds, canals, causeways and ringed ditches around moated cities have been found. Pottery in Brazil has been found and dated to 6000 BCE which is older than any pottery found in the Americas, The dates of pottery in South America seems to indicate a movement from Brazil to Guiana to the west coast of South America. Hunter gatherer evidence has been found as far back as 9200 BCE. The fact that these sites do not seem to correspond to the Clovis civilizations in North America is making it difficult to explain how the Americas were actually populated since the original theories of movement across the Bering strait down through North, Central and then South America aren’t necessarily supported by the evidence found so far.

(The Great Courses – Lost Worlds of South America)