Today, cutting-edge astronomers use space-based observatories to gain a sharp view of the stars and advance our understanding of the cosmos. But appreciation for celestial bodies dates back to ancient times. Many cultures built structures in ways that suggest they were in tune with Earth's annual trek around the sun. Other structures appear to take constellations and planets into account. Click the "Next" arrow above to learn about 10 of these ancient observatories. Each page includes an image taken by GeoEye's Ikonos satellite, shown in this artist’s conception, as it flew 423 miles above Earth at an average speed of 17,000 miles per hour.