Long before Galileo turned his crude telescope toward the sky, humans built observatories. It’s all about tracking the passage of time; these structures were built in an effort to track the Sun, Moon, planets and stars, giving ancient cultures a calendar to know when to plant, when to harvest and more. This “technological edge” allowed cultures such as the Incas and Egyptians to flourish. Such privileged information allowing the ancients to predict the seasonal shifts must have seemed to come from divine inspiration. Even thousands of years later, achaeoastronomers still marvel at the celestial knowledge displayed by some of these cultures. Here are some of the greatest astronomical observatories of the ancient world.
10. Machu Picchu
Situated high in the Andes Mountains in Peru, Machu Picchu wasn’t even discovered by western archaeologists until Hiram Bingham stumbled upon it in 1911. Many of the structures throughout the complex have alignments corresponding with the June solstice position of the rising and setting Sun; this is actually the winter solstice, as Machu Picchu sits in the Southern Hemisphere. The Sacred Plaza and the Temple of the Three Windows are all open and face the solstice sunset. A stone within the Torreon, known as the Temple of the Sun, is also struck by sunlight during the June solstice.
9. Easter Island
It is a mystery why people known as the Rapa Nui erected hundreds of stone statues, or moai, on remote Easter Island. The Rapa Nui began building these statues, hewn from volcanic rock, around 1200 AD. Any astronomical alignments intended by the original builders are unclear, although seven of the statues located at Ahu Akivi face the direction of sunset during the equinoxes. These are also unique as the only statues on the island facing out to sea, rather than inland.
8. The Ring of Brodgar
Located on the Orkney Islands in Scotland, the nearly complete Ring of Brodgar has a diameter of 300 feet. The ring, along with the nearby Stenness Stones, is believed to have been built during the Bronze age, between 3000 to 2000 BC. Alignments between the rocks and nearby hills correspond with ancient-period equinox, solstice and cross-quarter dates. These have shifted slightly during the intervening years, as the Earth’s axis makes its once-every-26,000-years wobble known as the precession of the equinoxes.
7. Chichen Itza
The Pyramid of Kukulkan on Mexico’s Yucatan Peninsula rings in the year’s two solstices in dramatic fashion. At sunset during the solstice, the alignment of the stones projects a luminous serpent seen “slithering” down the steps of the temple toward a huge serpent’s head carved at the bottom of the stairway (see above photo). Built by the Maya between 1000 and 1200 AD, numbers incorporated into the construction of the temple are also significant, such as 365 steps on four sides (for the number of days in the year). The nine terraces are divided into two, representing the eighteen months in the Maya calendar.
This large tomb in Drogheda, Ireland, was discovered in 1699 and dates to around 3200 BC. The tomb is surrounded by a ring of stones decorated with solar motifs, and a larger ring of large boulders spanning a diameter of 340 feet. But it’s the inner passageway alignment that makes Newgrange special. Right around the winter solstice from December 19-23, sunlight pierces the entrance to the 58-foot-long passage to light up the inner chamber during sunrise. The entire light display lasts for about 17 minutes.
5. Gaocheng Astronomical Observatory
Built in 1279 AD in China’s Henan province, the large Gaocheng Astronomical Observatory stands on a site used for astronomical measurements for thousands of years. The complex serves as a large transit instrument, measuring the exact time the Sun stands highest to the south at local solar noon. Also known as Dengfeng Observatory, the structure served to refine the Chinese calendar, and accurately measured the length of the tropical year three centuries before Europeans achieved that feat. Like many of these other ancient observatories, the United Nations has designated Gaocheng a World Heritage Site.
4. Chaco Canyon
Located in the northwestern corner of New Mexico, Chaco Canyon civilization reached its zenith around the 10th century AD. The ancient Pueblo inhabitants of Chaco Canyon were obviously interested in celestial events, as illustrated by several alignments. One, known as the “Sun Dagger,” causes a beam of sunlight to pierce a spiral rock engraving, and records solstice and equinox cycles. Chaco Canyon’s astronomers also went one step further, and knew how to record the 19-year cycle of the Moon measuring the period of minor and major lunar standstills.
3. Angkor Wat
The ancient Khmer temple complex of Angkor Wat in Cambodia is a sprawling, amazing sight. Although built for religious purposes, in 1976 researchers uncovered what may have been astronomical alignments in Angkor. From one nearby hilltop shrine, an observer can see the Sun setting over the main temple at Angkor during the winter solstice. Six months later, an observer standing at the southwestern corner of Angkor Thom can see the Sun rise through the eastern gate during the summer solstice.
The Egyptians were highly accomplished astronomers, and the Karnak temple complex may have been their ultimate astronomical observatory. Early 20th century astronomer Norman Lockyer noted that at least four temples at Karnak match stellar alignments that were present at the time the temple was built. Lockyer also pointed out that Karnak could be used to calculate the length of the year with great accuracy. Millions of tourists visit this site in Luxor each year.
Constructed over a period of a millennium starting around 2950 BC, modern archaeoastronomers have identified many celestial alignments at Stonehenge. The most famous of these occurs on June 21 on the summer solstice, when the rising Sun is seen to balance on the Heel Stone as it shines down the long, wide lane known as the Avenue. It’s worth noting that scientists debate whether all of the celestial alignments found at Stonehenge and other ancient observatories were intentional, or merely a coincidence noted by modern man. For example, in Manhattan, the Sun shines down east-west aligned streets during the equinoxes, in a modern phenomenon known as “Manhattan-henge.”