Transcript: When you think of the calendar that we use every day some questions arise.  Why do you have to count on your knuckles or remember a rhyme to figure out how many days there are in a month?  Why does the year start in January as opposed to any other time? Why is December named after the Latin word for "ten" when in fact it is the twelfth month?  To answer these and other questions about the quirks in our calendar we have to go back to the early Romans.  The calendar we use is based...

Transcript: The early Greek philosophers had none of the tools of modern science.  They did not have the machines with which to probe the atom.  They did not have telescopes. They didn't have modern technology of any kind, and yet with logic and mathematics they were able to make some striking speculations and discoveries about their universe.  They speculated as to the existence of atoms.  They speculated that the Earth was round and imbedded in a large cosmos.  They speculated as to the...

Transcript: A calendar is a way of keeping track of the days in a year or the time it takes for the Earth to go from one place in its orbit to the same place one orbit later.  The first calendars date back 5000 years to the Babylonian and Egyptian Cultures.  The earliest calendars had 360 days, and this fact became the basis for our system of measuring angle and of keeping track of time, the subdivisions of an hour and of a minute.  The Babylonians eventually had a calendar that was accurate...

Transcript: The simplest division of time used by hunter-gatherers was to divide the day into the time when the sun was rising, ahead of the Meridian, and the time the sun was setting, beyond the Meridian.  We still use that terminology.  "AM" means "Anti-Meridian," or before the Meridian. "PM" means "Post-Meridian," or past the Meridian. So the first people divided the day into two, roughly equal parts.  The practice of dividing a day into hours originated 4 or 5000 years ago with the...

Transcript: It is fundamental to how science works, and to our understanding of the everyday world, that events have causes.  This is called Determinism.  Sometimes our belief that events have causes leads us to confuse causation and correlation. Bertrand Russell told the story of a chicken growing up on a farm. Every day the Sun rose and the chicken was fed.  The chicken came to associate the Sun rising with being fed and believed that one caused the other.  One day the farmer comes out...

Transcript: Suppose you have a small particle or a grain of sand and a fine knife and you divide the grain of sand in half, and then in half again, and then in half again.  Is there an end to this process, or must you reach a limit, an indivisible particle?  Democritus, the fifth century BC Greek philosopher, imagined that it was illogical that this process of subdivision of matter could continue without end, and so he proposed that all matter was made of atoms, indivisible, microscopic units...

Transcript: Every human culture has felt the need to subdivide time. In addition to the seasons, which follow from the Earth's motion around the sun, and months, which are tied to the lunar cycle, almost every culture has divided time into weeks. "Week" comes from the old German word meaning "to change." Weeks have had different numbers of days in different cultures through history. The modern tradition of a seven-day week actually dates back to the Babylonian times.  The word “Sabbath” is a...

Transcript: The constellations of the night sky are among the oldest human artifacts.  For thousands of years humans have been noticing patterns and using them to navigate, or to keep track of the sky, or to tell myths and legends.  There are 104 constellations in the modern sky.  Some of them are extremely old. There is evidence that Ursa Major, the great bear, which includes the asterism of the Big Dipper, dates back to at least 10,000 years.  Asian tribes named this constellation, and...

Transcript: The celestial sphere is an imaginary sphere surrounding the Earth onto which are projected the objects of the night sky.  There are several fixed points on the celestial sphere that are important.  The Zenith is the point directly over your head.  The Nadir is the point directly below your feet.  The line drawn across the sky that represents the highest elevation of the sun or any other object as it traverses the sky is called the Meridian.  The sun rises through to its highest...

Transcript: Humans has been anatomically modern for about 40 or 50,000 years.  If you can imagine what life would have been like 30 or 40,000 years ago for hunter-gatherers somewhere in Europe or Africa or the plains of Asia, you can realize that the sky must have been important to them.  The first use of astronomy was not in the modern, scientific sense.  Astronomy and the stars and the sky were a fundamental part of people's lives. The sky was a map, a clock, a calendar, a source of myth...

Transcript: Aristotle, who lived in the fourth century BC, was the most influential and famous Greek philosopher.  He founded a second University, the Lyceum, near Athens. He was a pupil of Plato.  He wrote and lectured on many subjects, including marine biology, botany, anatomy, economics, politics and meteorology.  He developed the tools of logic that are the basis of the scientific method.  He had his own observatory, and he made observations of stars and planets.  In cosmology he...

Transcript: Aristarchus, who lived in the third century BC, was a skilled geometer, and he anticipated the Copernican heliocentric model by over 1800 years.  He deduced by application of logic and geometry that the sun must be 19 or 20 times larger and further away than the moon.  Knowing that the sun was larger than the Earth it made no sense for the sun to go around the smaller Earth.  Rather, Aristarchus supposed that the smaller object went round the larger object.  He used the analogy of...

Transcript: It took a long time for people to figure out the true sizes and distances of celestial objects.  Part of the reason is psychological. It was always difficult for humans to imagine that there might be things so much larger then them or so much larger than the Earth.  The other reason is that when you look at something in the sky all you can really see is its angular extent, and its angular extent tells you nothing about its true distance or true physical size.  For example, when...

Transcript: For tens of thousands of years humans have used the sky, the daytime sky and the night sky, as a map, a clock, and a calendar.  The first astronomy thus is directly tied into human culture, into the needs for hunter gatherers to move around, follow the migrating herds, garnish food sources, and protect themselves from the extremes of climate.  The first astronomers were not scientists in the modern sense of the word; they used careful observations made systematically, in cases...

Transcript: Anaximenes was a student of Anaximander and also from Aletes in Turkey.  He believed that the source of all things was air and that the diversity arose from changes in the primordial substance, that the universe had an underlying homogeneity.  That is also a strikingly modern idea because we believe that the universe today had all of its structure emerge from an initially uniform, hot state. Anaximenes believed that the Earth was flat and that it floated on air.  This is not a...

Transcript: The oldest surviving fragment of philosophy dates back to Anaximander in the sixth century BC. Anaximander wrote that the universe was made of a primordial substance and that this primordial substance was infinite in extent.  This is the first known use of the concept of infinity in science.  He also supposed that the primordial substance had no intrinsic color, odor, or weight, that these were all secondary attributes, another strikingly modern idea.  He also wrote about how the...

Transcript: In the 5th century BC Anaxagoras deduced the true cause of eclipses. He realized that the curved shadow of the Earth on the Moon during a lunar eclipse supported the idea that the Earth was round.  In fact, a sphere is the only three-dimensional object that, whatever its orientation, always casts a circular shadow.  He was aware of a meteorite that had fallen in his native Greece and deduced from it that objects could move between the celestial and terrestrial spheres.  He also...