A vast, shadowy circle sits in a flat wheat field near Goseck, Germany. No, it is not a pattern made by tipsy graduate students. The circle represents the remains of the world's oldest observatory, dating back 7,000 years. Coupled with an etched disk recovered last year, the observatory suggests that Neolithic and Bronze Age people measured the heavens far earlier and more accurately than scientists had imagined.

Archaeologists reported the Goseck circle's identity and age this past August. First spotted by airplane, the circle is 75 meters wide. Originally, it consisted of four concentric circles--a mound, a ditch and two wooden palisades about the height of a person--in which stood three sets of gates facing southeast, southwest and north, respectively. On the winter solstice, someone at the center of the circles would see the sun rise and set through the southern gates.

Although aerial surveys have demarcated 200-odd similar circles scattered across Europe, the Goseck structure is the oldest and best preserved of the 20 excavated thus far, and it is the first circle whose function is evident. Though called the German Stonehenge, it precedes Stonehenge by at least two millennia. The linear designs on pottery shards found within the compound suggest that the observatory was built in 4900 B.C.

Perhaps the observatory's most curious aspect is that the roughly 100-degree span between the solstice gates corresponds with an angle on a bronze disk unearthed on a hilltop 25 kilometers away, near the town of Nebra. The Nebra disk, measuring 32 centimeters in diameter, dates from 1600 B.C. and is the oldest realistic representation of the cosmos yet found. It depicts a crescent moon, a circle that was probably the full moon, a cluster of seven stars interpreted to represent the Pleiades, scattered other stars and three arcs, all picked out in gold leaf from a background rendered violet-blue--apparently by applying rotten eggs.

The two opposing arcs, which run along the rim, are 82.5 degrees long and mark the sun's positions at sunrise and sunset. The lowest points of the two arcs are 97.5 degrees apart, signifying sunrise and sunset on the winter solstice in central Germany at the time. Likewise, the uppermost points mark sunrise and sunset on the summer solstice. The sun's position at solstice has shifted slightly over the past millennia, notes Wolfhard Schlosser of the Ruhr University in Bochum, so that the angle between sunrise and sunset is now slightly farther apart than when the Nebra disk and the Goseck circle were made (by 1.6 and 2.8 degrees, respectively).

Nearby excavations of wood-and-clay houses have turned up a variety of grains and evidence of domesticated goats, sheep, pigs and cows. Farmers reached this part of the world some 500 years before they built the solar observatory. Although these earliest Neolithic agriculturists most likely measured only the sun's movements, over millennia they came to quantify the lunar cycle and the positions of constellations. The Pleiades, which depart the northern sky in spring and reappear in the fall, still mark crop cycles for many farmers around the world. The Nebra disk may have been a ritual object or, more likely--given its precision--a calculational tool used with observations at Goseck or a similar site to determine planting and harvest times.

The third arc on the disk, believes Francois Bertemes of the University of Halle-Wittenberg, is the stuff of legend. The ancients did not understand how the sun could set in the west and end up in the east the next morning. Representations of a disk in a ship, from Bronze Age Egypt and Scandinavia, reveal an age-old belief that a ship carried the sun across the night sky. The Nebra disk is the first evidence of such a faith in central Europe. That the land-bound cultivators knew of ships is no surprise: Bertemes points out that travelers spread the latest in Bronze Age technology as well as mythology.