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In this episode of NASA Connect, learn how ancient cultures observed seasonal cycles

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and how the sun played a part in their observations.

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We'll also conduct a cool hands-on activity measuring shadows created by the sun and a

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gnomon.

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Stay tuned for another exciting episode of NASA Connect, Ancient Observatories.

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Kamae toau, or welcome to NASA Connect.

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I'm Jennifer Foley and this is the National Museum of the American Indian.

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And I'm Dr. Stan Odenwald at an archeological site in Mexico.

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Hola.

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This is NASA Connect, the show that connects you to math, science, technology...

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And NASA.

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On today's program, you will see how ancient cultures found a connection to the stars.

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You will also learn how many of these societies were very sophisticated when making celestial

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observations.

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You'll also learn about the mathematics and geometry used by these ancient peoples to

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make their observations.

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What you will learn today will absolutely astound you.

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But first, Jennifer, tell us about that building that you're in.

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Stan, this is the newest museum in our nation's capital.

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As you enter the museum, hundreds of written and spoken words meaning welcome in native

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languages throughout the Americas are projected onto this wall.

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These people, not only here in the Americas, but also their brothers and sisters in Africa,

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Asia, Europe, and the Pacific, looked at our starry skies.

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All of these people had a connection to the sun.

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In the museum, this room celebrates the sun.

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From this circle, the four cardinal directions, north, south, east, and west, extend out of

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the building.

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The angles of solstices and equinoxes are mapped on the floor.

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A light spectrum is cast by the sun, which shines through the prisms set into the south-facing

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wall.

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Each prism is sighted to the sun for a particular time of day and season.

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The dramatic designs in this modern museum show the connection between astronomy, nature,

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and people.

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That connection is the key to understanding how the ancients looked at our universe, which

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is the theme of today's program.

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Today, we will talk to Native American astronomers.

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Dr. Stan Odenwald will treat us to the foundations of astronomy as we know it today.

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And he will fill us in on the celestial accomplishments of the Mayans.

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Throughout the program, you will be asked to answer several inquiry-based questions.

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After the questions appear on the screen, your teacher will pause the program to allow

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you time to answer and discuss the questions.

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This is your time to explore and become critical thinkers.

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Now, let's learn more about ancient observatories.

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The science of interpreting the relationship between the sun and the daily lives of primitive

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people is called archaeoastronomy.

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Archaeo meaning archaeology, and astronomy meaning the study of stars.

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Observing celestial phenomena is the one constant that unifies humankind throughout space and

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time.

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Ancient man knew celestial events followed cycles, circles, and these events could be

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recorded.

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Approximately 5,000 years ago, they devised a way to place stones in certain positions

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to align for lunar and solar events.

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Events like seasons were noted and found to recur regularly with certain positions of

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the sun and stars.

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The Earth spins on its axis once every day and gives us the familiar experience of daytime

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and nighttime.

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For thousands of years, humans have used this cosmic cycle to regulate their work day, their

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meals, and their sleep.

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The Earth orbits the sun once every year, and from this we get the familiar 365-day

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cycle.

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Earth's orbit around the sun is an ellipse.

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Basically, that means an oval with the sun offset from the center of the ellipse.

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Does this mean that we have summer when the Earth is closest to the sun and winter when

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the Earth is farthest from the sun?

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The surprising fact is that the distance from the Earth to the sun has absolutely nothing

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to do with the changing seasons.

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Our northern hemisphere is closest to the sun in January and farthest from the sun in

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July.

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So what is causing the change in temperature?

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Earth's axis is tilted by 23.5 degrees from a line perpendicular to Earth's orbit.

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What does this mean?

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To understand this tilt, we have to use a bit of basic geometry.

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An angle has two sides and a vertex.

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The sides are rays that share a common endpoint called the vertex.

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The angle formed by two rays can be named in a variety of ways.

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For example, the angle formed by ray AB and ray AC can be named angle BAC, angle CAB,

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or angle A for short.

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Notice that A must be the middle letter in both three-letter names because it's the vertex.

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You can measure angles using a protractor.

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The unit of measure is degrees.

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Angles can be classified by their measures as acute, right, obtuse, and straight.

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If the Earth rotated on its axis perpendicular to or at a right angle to the orbit, there

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would be no changes in temperature.

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The Earth rotates at an angle 23.5 degrees from this perpendicular line.

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It's a very small tilt, but enough to affect the sun's rays hitting the Earth.

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This is a great time to pause the program and think about the following questions.

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Why is the area near Earth's equator hotter than the areas near the poles?

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If the tilt of Earth's axis measured 33 degrees rather than 23.5, how might seasonal changes

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and temperature ranges differ?

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Teachers, it's now time to pause the program.

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The tilt of the Earth's axis gives us our seasons.

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And because of the extremes in heat and cold, it's very important to keep track of the changing

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seasons if you're growing food.

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This seasonal cycle is important to ancient and even modern people.

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In some parts of the world, like the arid climates of the southwest states of the USA,

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the growing season was so short that people could not waste much time getting the seeds

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in the ground at the start of spring.

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But how do we predict when the growing season will begin in the spring?

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For that matter, how can we tell when the other seasons begin and end?

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It turns out that just by keeping track of how high up the sun gets over the horizon

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at noon, you can determine the start of the seasons exactly.

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Almost all ancient people that relied on planting times discovered this little relationship.

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The start of the four seasons, summer, fall, winter, and spring, are noted by what astronomers

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call the summer solstice, the fall equinox, the winter solstice, and the spring equinox.

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At the start of summer around June 21st in the northern hemisphere, the sun is at its

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highest point above the horizon at noon.

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As the sun begins its movement back away from its maximum height, the number of daylight

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hours has declined to an equal number of daylight and nighttime hours.

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This is the fall equinox near September 21st.

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A few months later, the path of the sun arrives at its lowest point at noon.

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The sun spends very little time above the horizon of the northern hemisphere, and the

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night is much longer than day.

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Welcome to the winter solstice, or start of winter, around December 21st.

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After a few more months, the path of the sun works its way higher in the sky, eventually

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arriving at a path where day and night are equal.

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This happens March 21st at the spring equinox, a vital time for planting crops.

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Archaeoastronomers have found three types of early observatories.

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Simple markers, circles of stone and wood, and temples.

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Early on, markers were used to create sight lines to the horizon, so that during the equinox

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or solstice, the sun would appear to rise exactly on the sight line.

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Stonehenge in England was set up this way, as were a number of ancient Native American

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buildings, such as the ones at Chaco Canyon in New Mexico and Hovenweep in Utah.

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England's Stonehenge is one of the earliest examples of an observatory in Europe.

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Stonehenge is a large calendar, capable of predicting the equinoxes and the solstice.

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Before Stonehenge, in 3000 BC, the ancient Egyptians had devised a solar calendar of

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365 days, the starting point of which hinged on the helical rising of the star Sirius,

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which also happened to coincide with the summer solstice and the annual flooding of the Nile.

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By being in touch with celestial phenomenon and their natural surroundings, the ancient

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Egyptians were able to predict events of great significance in their desert environment.

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At Abu Simbel, massively carved statues of Ramses the Great face east to greet the sun

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god Ray, the bringer of light.

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As the sun rises each day, the statues are illuminated again, perhaps a sign of rebirth

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for Ramses.

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But the most compelling is a passage to the temple's inner sanctuary, which is aligned

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so that on October 18th, the sun filters into the sanctuary, illuminating a statue of Ramses.

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While October 18th doesn't mean much to us in the Western world, this October date corresponds

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to the beginning of the Egyptian civil year and the celebration that occurred during the

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time in which Ramses lived.

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It was the Greeks, however, that created the first portable cosmological tool for keeping

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track of these motions, a stick.

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The Greeks actually called it a gnomon, and it was used to keep track of the shadow of

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the sun.

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Actually, it's a little bit more difficult than that because the shadow depends on your

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latitude.

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Again, if you are not near the equator, the shadow will be shortest during the summer

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solstice and longest during the winter solstice.

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For the spring equinox and fall equinox, the shadow will be halfway between the shadow

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lengths at the solstices.

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In the southern hemisphere, the shadows will be reversed, just as you all know the seasons

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are reversed.

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When it's summer in the United States, it's winter in Argentina.

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This all works pretty well if you're not at the equator.

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At the equator, the summer solstice sun casts a shadow in the southerly direction, and the

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winter solstice sun casts a shadow in the northerly direction.

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During the equinox, at the equator, the shadow disappears.

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Oh, and another thing that they were used for is sundials, and it looks to me like it's

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time to go back to Jennifer.

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Okay, guys, let's take a look at how a gnomon works and see the angle of the sun at certain

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times during the day.

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Students from Newcomb Elementary School in Newcomb, New Mexico, will preview this show's

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hands-on activity.

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Yá'át'ééh, hello!

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We are students from Newcomb Elementary School.

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We are located on the Navajo reservation in the Four Corners region of New Mexico.

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Tracking the passage of the sun in the sky continues to play a very important role in

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the life of our Navajo culture.

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Traditional Navajos still use this system of tracking the sun's shadows to tell time

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and to tell the changing of the seasons.

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For example, when my grandfather herd sheep, he does not wear a watch like this.

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He uses the sun's shadow to tell time.

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It also helps him to tell when to take the sheep back home in their corral.

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It also helps him to tell when to plant corn and watermelon on his farm.

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NASA Connect asked us to show you this program's hands-on activity.

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In this activity, the students will make sun shadow plots every half hour, marking the

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ends of the shadows made by the sun and a gnomon.

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You can download a copy of the Educator Guide from the NASA Connect website for directions

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and a list of materials.

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Turn a cardboard box upside down.

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Tape a large piece of paper to the cardboard box.

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Draw two lines that are perpendicular to each other, from top to bottom, and the other from

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left to right across the paper.

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Mark its center with a dot.

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And make a very small hole in the center of the box using the point of a scissors.

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Stick the gnomon through the dot and the hole in the cardboard.

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Secure it with tape so that 10 centimeters is sticking straight up out of the box.

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Use a protractor to make sure the gnomon is perpendicular to the box.

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On a clear, sunny day, find a large, flat area.

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Tape the box to the ground on all four sides.

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Starting as early in the morning as possible, mark the end of the gnomon's shadow every

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half hour until the end of the day.

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Next to the dot, label the time of the day it was marked.

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You will analyze the data you collect by measuring angles and length.

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Remove the gnomon and draw a straight line from each dot to the hole that the gnomon

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was placed in.

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Measure and record the angle between the horizontal line drawn through the center of

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the paper and each marked shadow.

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Then, measure and record the length of each shadow.

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Using geometry, find and label true north on your sun-shadow plot.

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Verify local solar noon using shadow length times and sunrise-sunset times.

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How do the lengths, positions, and angles of the shadows change?

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What do the changes tell you about the position of the sun throughout the day?

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Would the curve change if you used a different-sized gnomon to cast the shadow?

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And don't forget to check out this cool web activity for this program.

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You can download it from the NASA Connect website.

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Great job, you guys.

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All right, let's review.

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We've seen how ancient cultures used the sun-earth connection to mark the season.

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And you've seen an activity which uses the placement of shadows to record the

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movement of the sun across the sky.

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Research regarding Native American astronomy has recently begun to gain

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headway in archaeoastronomy.

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Let's look at the ways native cultures in the Americas use the sun-earth connection.

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Nancy Maryboy and David Begay are two indigenous astronomers from the Navajo Nation.

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Yá'át'ééh. Hello.

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We're here in Hovenweep National Park in southern Utah.

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I'm a Cherokee Navajo.

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I live not far from here.

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And I'm an educator on the Navajo Nation.

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A cultural astronomer means you deal with the astronomy of your own culture.

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And we put things within the context of a native worldview.

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Right behind me on the boulder, you can see an indication of a solar phenomena.

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On the boulder, there's two images.

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One's a concentric circle.

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One's a spiral.

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As the sun begins to rise, shafts of light come in from each direction.

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And as the sun continues to rise, the lights meet in the center.

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This only happens once a year.

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This phenomena occurs on the longest day of the year and is a very appropriate way to mark time.

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This can be a very harsh environment to live in.

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It can be hot, it can be cold, and it can be very dry.

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In order to survive, people had to live in accordance with the natural environment.

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And that meant the natural cosmic environment, the sun, the moon, and the stars.

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It was very important to track the path of the sun and the moon and certain constellations.

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And to do that, people used natural markers like petroglyphs and sun and moon alignments.

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Remember, there was no watches, there was no timekeepers, there was no calendars.

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My name is David Begay.

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I am a cultural astronomer.

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I've been living out here for many years.

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My clan is Maidishkeezhnee.

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This clan is a descendant from the Jemez Pueblo people.

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And here is one of the structures at Hovenweet National Monument.

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This structure had many purposes, one of which was an observatory.

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The ancient had a profound respect for the movement of the sun and the stars.

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On the longest day of the year, the sun shines through an opening and the light falls on a marker.

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What people experience here is really a cultural experience.

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It's a whole life experience.

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People felt the movement of the sun, people felt the movement of the moon.

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It was a daily experience.

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Among the Navajo people, for the sun, when it reaches summer solstice, it's a total life experience.

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People used to talk about the solstice being a four-day phenomenon.

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People used to say,

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The sun spent four days before it starts moving back the other way.

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So it's really something that was experienced, it was talked about, it was a part of the culture,

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it's been passed down through the generations.

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I think people talk about these movements in terms of days.

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I'm not sure if you can really call it special math.

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I don't think tracking the sun down to the second was important at that time.

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These buildings and boulders are remnants of ancient civilizations,

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much like the ruins in Rome, the ruins in Greece.

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And today, they're still very relevant to us out here in the southwest.

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We still see the same sky, and we're in awe of the technology that was employed

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to build these buildings and capture these solar and lunar alignments.

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Today, we look in the sky, we use some of the same knowledge that the ancestral Pueblans used.

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We use it for planting, we use it for setting ceremonies, and we use it to keep the earth in order.

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The balance between earth and sky is still very important to native peoples.

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Thanks, Nancy, and thanks, David.

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You know, guys, one of the earliest Native American structures to observe the sun and the stars is Casa Rinconada,

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located in the Chaco Cultural National Historical Park.

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Casa Rinconada is a large kiva.

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Kivas are large, circular rooms used for ceremonies by Native American cultures.

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Like Hovenweep, on the day of the summer solstice, a beam of light from an opening in the kiva

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precisely illuminates a niche in the far wall.

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For years, Chaco Canyon was primarily seen as a trade center,

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but with the advent of archaeoastronomy, Chaco is beginning to be seen as a center of astronomy and cosmology.

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So far on today's program, we have seen how the relationship between the sun and the earth

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weaved a connection between all ancient cultures.

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Now, much of the information from those cultures has been lost to us.

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However, other cultures have recorded that information, and now that information is being interpreted.

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For a look at one of these ancient cultures, let's return to Dr. Stan Odenwald.

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Thanks, Chen.

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Perhaps the greatest ancient astronomers were the Mayans, who lived right here where I'm standing.

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The Mayans inhabited the Yucatan Peninsula in Mexico and Guatemala.

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These people made astronomical and seasonal observations which rivaled anything seen in Europe

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during the Roman Empire or the Dark Ages.

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These amazing people mapped the heavens, they evolved the only true writing system native to the Americans,

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and they were masters of mathematics.

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They invented calendars that are still accurate today.

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And without metal tools, beasts of burden, or even the wheel,

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they were able to construct vast cities with an amazing degree of architectural perfection and variety.

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The largest structure at this site is El Castillo, the castle.

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That these temple builders were mathematically precise in their architectural designs

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is borne out by the natural phenomena which occurred during the fall and spring equinoxes.

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In the spring, as the sun rises, the shadow cast on the steps appear to form the body of a serpent

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which slithers down the stairs.

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Here at Chichen Itza, there is a structure unlike anything else ever created by the ancient Mayans.

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It's called El Caracol, and it actually looks like a modern observatory.

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Its design didn't function the same way as our modern observatories.

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Instead, its walls contain many windows.

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Inside the dome, stones could be removed, enabling the Mayan astronomers to observe different parts of the sky.

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The Mayans looked at the sky differently from any other civilization.

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Being near the equator, the equinox passages were easier and more accurate to determine

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because the sun cast no shadow at local noon during this time.

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They also had great veneration for the Milky Way.

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They called it the World Tree.

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The star clouds that formed the Milky Way were seen as the tree of life from which all life came.

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The Mayans also had their unique constellations.

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Like today's zodiac, they had their scorpion.

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Gemini, which appears to us as twins, however, was seen as a peccary,

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a nocturnal animal in the pig family.

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Other zodiac symbols were a jaguar, a bat, a turtle, the tail of a rattlesnake, and a sea monster.

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Because they looked at things differently, perhaps it's not surprising that the Mayans had a different mathematics as well.

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We use a numbering system based on 10 digits, but the Mayans used a system based on the number 20.

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Sounds a little bit complicated, but in fact it was more efficient for counting

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than some of the older systems used in Europe a long time ago.

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The Mayan counting system required only three symbols,

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a shell representing 0, a dot representing a value of 1, a bar representing 5,

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and a shell with a dot representing the base number 20.

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There are two advantages to the Mayan counting system.

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The first of these is the idea of zero, which many civilizations at that time did not have.

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Second, they only used three symbols to represent lower and higher numbers.

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In Rome, multiple symbols were used.

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I's for 1, V for 5, X for 10, L for 50, C for 100, and M for 1000.

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Mayan numbers were written from bottom to top,

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so the number 19 becomes bars of 5, 5, 5, with four dots above the bars.

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To complete the first set of 20, a dot was raised over a shell-like symbol.

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To get 21, the elevated placement of the dot remained to represent 20,

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and a dot was added underneath to represent 21.

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Then the counting cycle for the next 20 began again.

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So what do you think the number 40 or 41 would look like?

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In Europe at this time, people still struggled with the Roman numeral system.

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That system suffered from two serious defects.

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First, there was no zero.

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And second, Roman numbers were entirely symbolic,

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having no direct connection to the number of items represented.

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So, are you ready for a challenge?

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Okay.

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Working together, try adding 21 and 33 using the Mayan system.

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Then try adding 21 and 33 using Roman numerals.

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This is a good time to pause the program.

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So how did you do?

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Let's check your work.

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In Mayan, the number 21 is represented as dot, dot.

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33 is two bars equaling 10, three dots for units,

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and an elevated dot representing 20.

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Adding together, you get 54, which is two bars, four dots, and two elevated dots.

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Easy to decipher.

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In Roman, you have XXI plus XXXIII equals LIV.

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Unless you actually know what the Roman symbols stand for,

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you have no idea what you are seeing.

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In Mayan, you can actually add up the dots, bars, and shells.

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Mayan merchants often used cocoa beans, sticks, and shells to do these calculations.

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From these three symbols, the Mayans could do everything

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from the simplest arithmetic needed for trade

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to keeping track of astronomical events, both past and future.

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Speaking of astronomy, remember how I said the Earth's axis was tilted at 23.5 degrees?

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If you round that to 24, how would you write that in Mayan?

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The Mayan system of counting using dots, bars, and shells

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can be compared with the ones and zeros used by modern computers,

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and it was all done 1,500 years ago.

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With all the advances that the Mayans made,

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it's interesting to speculate what would have happened

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if the Mayans had sailed east to discover Europe

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instead of the Europeans sailing west to discover the Americas.

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To learn more about Mayan mathematics, go to the following websites.

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Back to you, Jennifer.

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Thanks, Stan.

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Well, guys, that wraps up another episode of NASA Connect.

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We'd like to thank everyone who helped make this program possible.

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Got a comment, question, or suggestion?

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Then email them to connect at lark.nasa.gov.

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I'd like to leave you guys with a thought and a challenge.

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What is impressive about these sites is the accuracy of their observations

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and the time and effort they put into building these observatories.

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Looking back at these buildings and places,

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we see that the ancients had a natural connection to their environments

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and that they were also capable of high-tech accomplishments in their own times.

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So now here's my challenge.

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How do you think people 300 or even 1,000 years from now

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will see us through the artifacts that we leave behind?

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Until next time, stay connected to math, science, technology, and NASA.

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Goodbye for now.

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NASA Jet Propulsion Laboratory, California Institute of Technology

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It revolves in different positions.

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It will tell us if it's fall, spring, or summertime, wintertime.