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Subido el 28 de mayo de 2007 por EducaMadrid

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Second segment of NASA Connect Ancient Observatories explaining how the height of the sun relates to the growing seasons and the length of daylight. This segment describes how Ancient Egyptian and Greek cultures used astronomy in their lives. The segment also contains an activity for exploring how a gnomon works. In the activity students must track the shadows made by a gnomon in 30 minute intervals. The activity will teach students how the length of the shadows and the angles created by the gnomon are related to the position of the sun.

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Archeoastronomers have found three types of early observatories, simple markers, circles 00:00:00
of stone and wood, and temples. 00:00:08
Early on, markers were used to create sight lines to the horizon, so that during the equinox 00:00:12
or solstice, the sun would appear to rise exactly on the sight line. 00:00:18
Stonehenge in England was set up this way, as were a number of ancient Native American 00:00:23
buildings such as the ones at Chaco Canyon in New Mexico and Hovenweep in Utah. 00:00:28
England's Stonehenge is one of the earliest examples of an observatory in Europe. 00:00:35
Stonehenge is a large calendar, capable of predicting the equinoxes and the solstice. 00:00:41
Before Stonehenge, in 3000 BC, the ancient Egyptians had devised a solar calendar of 00:00:46
365 days, the starting point of which hinged on the helical rising of the star Sirius, 00:00:52
which also happened to coincide with the summer solstice and the annual flooding of the Nile. 00:01:00
By being in touch with celestial phenomenon and their natural surroundings, the ancient 00:01:06
Egyptians were able to predict events of great significance in their desert environment. 00:01:11
At Abu Simbel, massively carved statues of Ramses the Great face east to greet the sun 00:01:18
god Ray, the bringer of light. 00:01:25
As the sun rises each day, the statues are illuminated again, perhaps a sign of rebirth 00:01:28
for Ramses. 00:01:35
But the most compelling is a passage to the temple's inner sanctuary, which is aligned 00:01:36
so that on October 18th, the sun filters into the sanctuary, illuminating a statue of Ramses. 00:01:42
While October 18th doesn't mean much to us in the Western world, this October date corresponds 00:01:50
to the beginning of the Egyptian civil year and the celebration that occurred during the 00:01:57
time in which Ramses lived. 00:02:02
It was the Greeks, however, that created the first portable cosmological tool for keeping 00:02:04
track of these motions, a stick. 00:02:08
The Greeks actually called it a gnomon, and it was used to keep track of the shadow of 00:02:11
the sun. 00:02:15
Actually, it's a little bit more difficult than that because the shadow depends on your 00:02:16
latitude. 00:02:20
Again, if you are not near the equator, the shadow will be shortest during the summer 00:02:21
solstice and longest during the winter solstice. 00:02:26
For the spring equinox and fall equinox, the shadow will be halfway between the shadow 00:02:29
lengths at the solstices. 00:02:34
In the southern hemisphere, the shadows will be reversed, just as you all know the seasons 00:02:37
are reversed. 00:02:41
When it's summer in the United States, it's winter in Argentina. 00:02:42
This all works pretty well if you're not at the equator. 00:02:46
At the equator, the summer solstice sun casts a shadow in the southerly direction, and the 00:02:49
winter solstice sun casts a shadow in the northerly direction. 00:02:54
During the equinox, at the equator, the shadow disappears. 00:02:58
Oh, and another thing that they were used for is sundials, and it looks to me like it's 00:03:02
time to go back to Jennifer. 00:03:06
Okay, guys, let's take a look at how a gnomon works and see the angle of the sun at certain 00:03:11
times during the day. 00:03:17
Students from Newcomb Elementary School in Newcomb, New Mexico, will preview this show's 00:03:19
hands-on activity. 00:03:23
Yá'át'ééh. 00:03:24
Hello. 00:03:25
We are students from Newcomb Elementary School. 00:03:26
We are located on the Navajo Reservation in the Four Corners region of New Mexico. 00:03:31
Tracking the passage of the sun in the sky continues to play a very important role in 00:03:38
the life of our Navajo culture. 00:03:43
Traditional Navajos still use this system of tracking the sun's shadows to tell time 00:03:45
and to tell the changing of the seasons. 00:03:50
For example, when my grandfather herd sheep, he does not wear a watch like this. 00:03:53
He uses the sun's shadow to tell time. 00:03:58
It also helps him to tell when to take the sheep back home in their corral. 00:04:01
It also helps him to tell when to plant corn and watermelon on his farm. 00:04:06
NASA Connect asked us to show you this program's hands-on activity. 00:04:11
In this activity, the students will make sun shadow plots every half hour, marking the 00:04:17
ends of the shadows made by the sun and a gnomon. 00:04:22
You can download a copy of the educator guide from the NASA Connect website for directions 00:04:27
and a list of materials. 00:04:32
Turn a cardboard box upside down. 00:04:34
Tape a large piece of paper to the cardboard box. 00:04:37
Draw two lines that are perpendicular to each other, from top to bottom, and the other from 00:04:41
left to right across the paper. 00:04:47
Mark its center with a dot. 00:04:50
And make a very small hole in the center of the box using the point of a scissors. 00:04:52
Stick the gnomon through the dot and the hole in the cardboard. 00:04:57
Secure it with tape so that 10 centimeters is sticking straight up out of the box. 00:05:02
Use a protractor to make sure the gnomon is perpendicular to the box. 00:05:08
On a clear, sunny day, find a large, flat area. 00:05:13
Tape the box to the ground on all four sides. 00:05:17
Starting as early in the morning as possible, mark the end of the gnomon's shadow every 00:05:21
half hour until the end of the day. 00:05:26
Next to the dot, label the time of the day it was marked. 00:05:29
You will analyze the data you collect by measuring angles and length. 00:05:33
Remove the gnomon and draw a straight line from each dot to the hole that the gnomon 00:05:38
was placed in. 00:05:44
Measure and record the angle between the horizontal line drawn through the center of the paper 00:05:45
and each marked shadow. 00:05:51
Then, measure and record the length of each shadow. 00:05:54
Using geometry, find and label true north on your sun-shadow plot. 00:05:59
Verify local solar noon using shadow length times and sunrise-sunset times. 00:06:05
How do the lengths, positions, and angles of the shadows change? 00:06:12
What do the changes tell you about the position of the sun throughout the day? 00:06:17
Would the curve change if you used a different sized gnomon to cast the shadow? 00:06:22
Don't forget to check out this cool web activity for this program. 00:06:28
You can download it from the NASA Connect website. 00:06:32
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Idioma/s:
en
Materias:
Matemáticas
Niveles educativos:
▼ Mostrar / ocultar niveles
      • Nivel Intermedio
Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
659
Fecha:
28 de mayo de 2007 - 16:54
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
06′ 36″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
480x360 píxeles
Tamaño:
39.72 MBytes

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