On the shortest day of the year - Dec. 21 - the shadow of one of the blocks disappears when the sun is directly above it.

"It is this block's alignment with the winter solstice that leads us to believe the site was once an astronomical observatory," said Mariana Petry Cabral, an archaeologist at the Amapa State Scientific and Technical Research Institute. "We may be also looking at the remnants of a sophisticated culture."

Anthropologists have long known that local indigenous populations were acute observers of the stars and sun. But the discovery of a physical structure that appears to incorporate this knowledge suggests pre-Columbian Indians in the Amazon rainforest may have been more sophisticated than previously suspected.

"Transforming this kind of knowledge into a monument; the transformation of something ephemeral into something concrete, could indicate the existence of a larger population and of a more complex social organization," Cabral said.

Cabral has been studying the site, near the village of Calcoene, just north of the equator in Amapa state in far northern Brazil, since last year. She believes it was once inhabited by the ancestors of the Palikur Indians, and while the blocks have not yet been submitted to carbon dating, she says pottery shards near the site indicate they are pre-Columbian and maybe older - as much as 2,000 years old.

Last month, archaeologists working on a hillside north of Lima, Peru, announced the discovery of the oldest astronomical observatory in the Western Hemisphere - giant stone carvings, apparently 4,200 years old, that align with sunrise and sunset on Dec. 21.

While the Incas, Mayans and Aztecs built large cities and huge rock structures, pre-Columbian Amazon societies built smaller settlements of wood and clay that quickly deteriorated in the hot, humid Amazon climate, disappearing centuries ago, archaeologists say.

Farmers and fishermen in the region around the Amazon site have long known about it, and the local press has dubbed it the "tropical Stonehenge." Archeologists got involved last year after geographers and geologists did a socio-economic survey of the area, by foot and helicopter, and noticed "the unique circular structure on top of the hill," Cabral said.

Scientists not involved in the discovery said it could prove valuable to understanding pre-Columbian societies in the Amazon.

"No one has ever described something like this before. This is an extremely novel find - a one of a kind type of thing," said Michael Heckenberger of the University of Florida's Department of Anthropology.

He said that while carbon dating and further excavation must be carried out, the find adds to a growing body of thought among archaeologists that prehistory in the Amazon region was more varied than had been believed.

"Given that astronomical objects, stars, constellations etc., have a major importance in much of Amazonian mythology and cosmology, it does not in any way surprise me that such an observatory exists," said Richard Callaghan, a professor of geography, anthropology and archaeology at the University of Calgary.

Brazilian archaeologists will return in August, when the rainy season ends, to carry out carbon dating and further excavations.

"The traditional image is that some time thousands of years ago small groups of tropical forest horticulturists arrived in the area and they never changed - (that) what we see today is just like it was 3,000 years ago," Heckenberger said. "This is one more thing that suggests that through the past thousands of years, societies have changed quite a lot."

Now a Chinese research team has found some clues. Its findings appeared in the June 26 edition of the U.S. journal the Proceedings of the National Academy of Sciences.

Using functional Magnetic Resonance Imaging (fMRI) to scan people's brains, the researchers found that native Chinese and English speakers treat numbers with different cortical parts of the brain.

In contrast to native English speakers who largely employ a language process that relies on the left perisylvian cortices for mental calculation such as a simple addition task, the researcherssaid, native Chinese speakers engage a visuo-premotor association network for the same task.

In both groups, the inferior parietal cortex of the brain was activated by a task for numerical quantity comparison, but furtheranalysis revealed a functional distinction between Chinese and English groups among the brain networks involved in the task.

The results indicate that different language systems, such as Chinese and English, can shape the way non-language-related content is processed. In other words, number processing differs in those with Chinese and English backgrounds, according to the team led by Yiyuan Tang, a professor at the Dalian University of Technology in China.

The team also noted that the brevity of the Chinese language for numbers allows for a larger short-term memory, and suggest that such faster processing in the language system might mean more efficient cortical activities in the brain.

Although language-specific processing may contribute to those differences, the learning environment and cultural variables may also have an influence on how numbers are acquired and represented in the brain. These factors may result in differential brain processes, the researchers added.

For example, reading and writing squared Chinese characters, which possess a high, nonlinear visual complexity, as well as using an abacus since elementary school, may help build a "mental image" of numbers in the brain.

"Those well formulated learning processes, which are beyond reading systems and are both educationally and socially different, may lead to brain differences during number processing and other cognitive tasks," the researchers concluded.

The initial orbit made possible the ability to obtain the first clues about the Venusian atmospheric dynamics on a global scale, before the spacecraft got closer and started observing the planet in greater detail.

During the spacecraft's orbital adjustment process, mission controllers used some of its instruments to perform the first observations at different distances from Venus - a few hours at a time from six different positions between April 12 and April 19.

Those observations produced images of a huge, double-eye atmospheric vortex over the south pole, not dissimilar from the equivalent structure present at the north pole - the only one previously studied in some detail.

Only glimpses of the stormy atmospheric behavior at the south pole were obtained by the Pioneer Venus and Mariner 10 missions, but such a double-eye structure never has been seen clearly before now.

High-velocity winds are known to spin westwards around the planet, and to take only four days to complete a rotation. This super-rotation, combined with the natural recycling of hot air in the atmosphere, would induce the formation of a vortex structure over each pole.

The question is why Venus is exhibiting two vortices.

"We still know very little about the mechanisms by which the super-rotation and the polar vortexes are linked," said Hakan Svedhem, ESA's Venus Express project scientist.

"Also, we are still not able to explain why the global atmospheric circulation of the planet results in a double and not single vortex formation at the poles," Svedhem added. "However the mission is just at the beginning and it's doing fine; we expect this and many other long-standing mysteries to be addressed and possibly solved by Venus Express."

Atmospheric vortexes are very complex structures that are very difficult to model, even on Earth. Thanks to these first pictures, it has also been possible to observe the presence of a collar of cold air around the vortex structure, possibly due to the recycling of cold air downwards.

Views of the Venusian southern hemisphere, taken in visible and ultraviolet light, show interesting atmospheric stripe-like structures. Spotted for the first time by Mariner 10 in the 1970s, they may be due to the presence of dust and aerosols in the atmosphere, but their true nature remains unexplained.

"Venus Express has the tools to investigate these structures in detail," Svedhem said. "Studies have already begun to dig into the properties of the complex wind fields on Venus, to understand the atmospheric dynamics on local and global scales."

Venus Express also made use for the first time ever from orbit of the so-called infrared windows present in the atmosphere of Venus - if observed at certain wavelengths, it is possible to detect thermal radiation leaking from the deepest atmospheric layers, revealing what lies beneath the dense cloud curtain situated at about 60 kilometers altitude.

The first infrared images making use of these windows show complex cloud structures, all revealed by the thermal radiation coming up from different atmospheric depths.

Venus Express also has compiled preliminary data about the chemical composition of the atmosphere. The planet's atmosphere is composed mainly of carbon dioxide. The incoming solar radiation dissociates this molecule into carbon monoxide (and oxygen in the upper atmospheric layers.

Venus Express already has spotted the presence of an oxygen airglow high in the atmosphere. However, the spacecraft's instruments have revealed the presence of carbon monoxide as low as the cloud-layer top.

Scientists will continue the data analysis and retrieval to understand the phenomenon, which is very important to clarify the complex chemical processes and cycles at work in the atmosphere of Venus under the influence of solar radiation.

Since May 7, Venus Express has been circling the planet in its final 24-hour orbit, ranging between 66,000 kilometers and 250 kilometers (40,920 miles and 155 miles), so it is now closer to the planet that during its capture orbits.

Venus Express scientists are now analyzing the new data, which already show what seem to be exciting new features. "We have never seen Venus in such great detail so far, Svedhem said. "We are eagerly waiting for these new data to be available."