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China Adventure

Journey to the Center of the Earth

Thursday, August 13, 2009

OK. As a science teacher I feel duty bound to post at least one science lesson for you guys, so here it goes :)

Yesterday we visited another amazing historically significant place on our journey- Gaocheng Astronomical Observatory in the Heneng Province- the oldest surviving observatory in China.

China has a history of astronomical observation and record keeping dating back more than 4000 years. Many cosmic objects and events have been observed, noted and interpreted by Chinese astronomers centuries before they first appeared in European records. In fact, China has a longer unbroken history of astronomical study than any civilization that has ever existed!

Ancient Chinese astronomy has proven very accurate over the years. NASA's Jet Propulsion Lab even recently used ancient Chinese eclipse timings (accurate to about 25 minutes) to learn more about the Earth' rotation.

Chinese astronomers are also credited with the earliest known map of the stars. Created sometime around 700 AD, it includes precisely drawn representations of over 1000 constellations.

One especially important astronomical tool in early Chinese astronomy was the gnomon- an object whose shadow is used to record the changing position of the sun. Many people feel that the gnomon we visited at Geochang is the most remarkable one ever constructed. It was created by the famous Chinese scientist, Guo Shou in 1279 AD to help determine the calendar dates associated with the four seasons and to help verify that Luoyang City (next to Geochang) was the center of China. He was assigned that duty by the Emperor who wanted Luoyang to become China's capitol city- a request that many around him did not agree with, so he had to establish a VERY good reason to support his desire. Since the Chinese at that time regarded China as the only country in the world, if Luoyang could be determined the center of China it would also, by default, become the center of the Earth- a very holy bestowal.

At noon on a clear day the gnomon's horizontal bar casts a shadow on a low stone wall that extends out from the center of the base of the gnomon tower. The wall was designed so carefully that it even has troughs carved throughout so well water could be added to check for levelness!

As the sun's path through the sky changed over the year, the location of the bar's shadow shifted along the wall. At the winter solstice, when the sun's path across the sky is as low as it's going to get all year, the shadow reaches out to its farthest point on the wall- vice versa for the summer solstice. When the shadow falls mid-way between these two points, the Autumnal and Vernal (Spring) Equinox can be determined. Guo Shou used the gnomon, along with other tools at the observatory, to mark the beginning and end of all four seasons AND to give the Emperor proof that Louyang was indeed the true epicenter of China.

That's it- lesson over! Now for you test...

1. Can you find the gnomon bar in the picture above? Where is it?

2. What is your favorite season? Why?

3. Was Guo Shou' assertation about the center of China correct? How do you know? Please explain.

Everyone who answers the above three questions in a reply to this post will be entered in a raffle for a special gift from China. I will announce the winner in one week. Good Luck!!!

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Changing Connections said...


As luck would have it, I had just finished a time consuming post giving a thumbnail sketch of all the teachers' posts....when I checked in on the China blog to find two more posts. You can read the post here: I am working on one that highlights the students for a bit later.

I am totally non-scientific, so please do not laugh at my answers. I'll try, though, because I have so enjoyed reading all the posts.

1. The gnomon bar is in the upper center of the photo, about 1/2 inch down from the roof's top crenelation. The gnomen bar is above what appears to be a line dividing two connected towers separated by the open space allowing the light to move through the gnomon. It looks like a chinning bar. (can you see why I do not teach science...)
2. My favorite season is a hybrid: late autumn and early spring. Both are equally excellent "seasons" for "the girls," since they are Andean mountain girls and the other seasons are much too warm for them. Their care is also easiest during these months.
3. I am totally out of my comfort zone here, but I think Guo Shou" proved his assertion with the perfect positioning of the sun to support the equinoxes by the position on the wall determined by the gnomon bar.

RJ Stangherlin
PA DEN LC Blog Coordinator

Karen Wells said...

From what I have learned about the Chinese from the blogs, it is no surprise that their star maps are as accurate as they are. As far as the are my answers:
1. The gnoman bar is located in the open space between the two towers. It is positioned slightly below the windows.
2. My favorite season is spring. Life is beginning, the flowers in my garden are bursting on the scene, and there is such promise in the air. I love the colors of fall but there is a sense of decline in this season.
3. I think Guo Sho was correct because he could prove by the equal shadows on the wall that all 4 seasons were exactly the same length thus this must have been the center of the world.

cavalava said...

Hi Heather! I have been following you all and wow! how exciting!I guess you now know why Wasser was so enthusiastic when he came back from China.
The bar is found across the top of the building in front of the space allowing light to pass through and create a shadow on the wall below.
My favorite season is summer because there is more time for friends,family,travel and most of all being outdoors!
If the city was not at the center of China ,the shadows would fall at an angle,not into the grooves Guo Shou created.Therefore his theory was correct.

viagra online said...

the journey to the center of the earth if it were real I would love to go, places where almost anyone to come! said...

it's really good i get the info about that earth middle or center point through this blog.....

Essential Programs Details

Duration 15 days
When August 1st - 14th, 2009
Focus History/Culture
Martial Arts
Modern/Ancient Architecture