The Sumerians were well aware that our solar system was Heliocentric. Moreover they show 11 celestial bodies or planets. The above picture taken from a Sumerian cylinder seal cleary shows that they not only knew the number of bodies in the solar system, but the relative size as well. There is a twelfth body shown away from the solar system. This would be Nibiru. Naturally this seal has led to major contraversy from both sides of the issue, though the old addage "A picture is worth a thousand words" applies quite well to this image. We will leave the contraversy to others, we only present the evidence

Editors Note: The position of the planets in the above picture also allows for the interpretation that there are nine planets and two moons, judging by the position of two of the bodies. If one remembers that the word "planet" literally meant "wanderer" and as such was used to describe any celestial body that moved through the heavens.

Websters Dictionary:
Etymology: Middle English planete, from Anglo-French, from Late Latin planeta, modification of Greek planEt-, planEs, literally, wanderer, from planasthai to wander ...
1 a : any of the seven celestial bodies sun, moon, Venus, Jupiter, Mars, Mercury, and Saturn that in ancient belief have motions of their own among the fixed stars b (1) : any of the large bodies that revolve around the sun in the solar system (2) : a similar body associated with another star c :
 

Bible Reference - Old Testiment:

In the Story of the family of Jacob...

Genesis 37 Verse 9

He dreamed yet another dream, and told it to his brothers, and said, "Behold, I have dreamed yet another dream: and behold, the sun and the moon and eleven stars bowed down to me."

Though this was from a dream, it still clearly shows that the people at the time of Jacob accepted the fact that there were11 planets or "wandering stars"

Zecharia Sitchin

This seal is the centerpiece of Sitchin’s theory that the Sumerians had advanced astronomical knowledge of the planetary bodies in our solar system. This knowledge was allegedly given to the Sumerians by extraterrestrials, whom Sitchin identifies as the Anunnaki gods of Sumero-Mesopotamian mythology. In the upper left-hand corner of the seal, Sitchin argues, one sees the sun surrounded by eleven globes. Since ancient peoples (including the Sumerians according to Sitchin) held the sun and moon to be “planets,” these eleven globes plus the sun add up to twelve planets. Of course, since we now know of nine planets plus our sun and moon, part of Sitchin’s argument is that the Sumerians knew of an extra planet beyond Pluto. This extra planet is considered by Sitchin to be Nibiru, an astronomical body mentioned in Mesopotamian texts. Sitchin’s works detail his contention that Nibiru passes through our solar system every 3600 years, and so some believers in Sitchin’s theory contend that Nibiru will return soon. Some followers of Sitchin’s ideas also refer to Nibiru as “Planet X”...  by Michael S. Heiser

Editors Note:  Michael S. Heiser disagrees with Sitchin's theory and has a website with both a counterview to Sitchin's theaory as well as one of his own : published  in "Facade". He does however have a well written page with many looks into Biblical translations of Ancient Hebrew and Aramaic texts. Of most interest to our research is Heiser's language evidence that clearly shows that Nibiru is a "gateway" not a "planet"

Related Links:

• Michael S. Heisers Website
• Zecharia Sitchin's Website

Blossom of Mesopotamian astronomy falls on the I thousand of years B.C. In 612 B.C. the capital of Assyria (Nineveh) was ruined by the Babylonian troops. Later an archaeologists found a lot of earthenware "books" of Assyrians priest-astronomers in the ruins of the palace of the last Assyrian tzar Ashurbanipal. There was a result of all fore coming development of astronomy. Apart from catalog of stars and constellations and their morning rise data list those "books" included a list of" constellation in the Moon way", that is 18 constellations - a prototype of modern zodiac.

Mesopotamia was covered by the net of temples, where they carried astronomical investigations. From the VIII-th century B.C. astronomers began to register the dates of observed Moon eclipses in special lists. Just the knowledge about ancient eclipses allowed Gipparch, Ptolemei and Copernicus calculate with more accuracy the year duration.

These ancient scientists observations are actual even nowadays but there is understatement of lack of accuracy in their measurement in detecting distance between the Sun and the "basic" stars. There main astronomical tool was a water watch. Mesopotamian astronomers divided a day (24 hours) into 12 hours and every hour was divided into 30 "time degrees". One time degree had four our minutes.

Zodiac circle of Assyrians. The most outstanding achievement of Mesopotamian astronomy became the development of mathematical theory, helped to fore measure the Moon and the planet moving with exactness enough for the naked eyed measurements.

During this epoch on a basis of long time observations it was discovered saros (Greek "repetition") i.e. 18-year period of the repeated Moon eclipses. It was also found the periodical law-governed nature of the planet movement. The classical scientists used the achievements of Mesopotamian science.

Source - Translation on Russian Think Quest Site