Throughout history, humans have watched the stars in the night sky. Observatories were built to aid in the study of celestial objects as a means of measuring time. Many calendars are based upon the information gathered through these observations, including the Julian and Gregorian calendars. Different cultures and countries built observatories of different kinds to study the skies and track their calendars.
Prehistoric and Early Observatories
Arguably the most well-known prehistoric observatory is Stonehenge in Wiltshire, England, a circle of massive stones arranged to align with certain celestial events. Stonehenge was used as a way of tracking the moon, stars, and eclipses. There are a number of other Neolithic structures throughout Europe similar to Stonehenge in design and serving a similar purpose.
Native Americans built rock pattern structures called medicine wheels, or spiritual healing sites, that are strongly connected to the night skies. The three most notable medicine wheels are located at Big Horn, Wyoming, in the United States and at Moose Mountain in central Saskatchewan and east of Calgary in Majorville, Alberta, Canada. Most medicine wheels are created of stones located on top of hills or mountains, and they consist of a central stone from which spokes radiate toward a rim.
The Mayans have written records of astronomical observations, and several of the Mayan buildings were architecturally designed around the heavens or for the purpose of observing the skies. One such building is the Caracol Tower in Chichen Itza, which has three windows used by Mayan astronomers for observations. The Mayan people used the information gathered through these observations as a source for creating the Mayan calendar.
In medieval Islam, there existed a desire to retain and elaborate upon the knowledge created by the ancient Greeks. Constructed in Baghdad, in what is now Iraq, during the Abbasid era of Islam, the House of Wisdom, a research center with observatory, enabled astronomers to create updated charts of planetary motion based on Ptolemy’s research.
Many observatories were destroyed or abandoned due to superstition or political conflict. One such research facility, also known as the House of Wisdom, was constructed in Cairo, Egypt early in the 11th century CE. The observatory was destroyed 100 years later due to the superstition held by the populace toward planetary observation and political strife. The Istanbul Observatory, built 500 years after the Egyptian House of Wisdom, met a similar fate for similar reasons.
Not all Islamic observatories met such ill-fated demise. The two most successful observatories in the Islamic world were located at Maragha, in modern- day Iran; and at Samarkand, in modern-day Uzbekistan. The Maragha observatory was originally constructed with astrological, rather than astronomical, intent. The major accomplishment associated with the Maragha observatory is the Ilkhanic tables charting the motion of the planets, the moon, and the sun. Fifteenth century astronomer Ulugh Beg used the ruins of the Maragha observatory as a model for the observatory at Samarkand built in the 15th century CE, where a sextant with a 120-foot radius was constructed. This instrument allowed for a resolution of arc seconds in its measurements, which was not to be surpassed until the invention of the telescope 200 years later. Astronomers at the Samarkand observatory recorded a list of nearly 1,000 stars visible from their location. Today, a crater on the moon is named after Ulugh Beg.
The Beijing observatory, built in the 15th century CE, was occupied by astronomers charged with watching the night skies. Over the course of 3,000 years, these astronomers had recorded data on hundreds of astronomical activities, including lunar and solar eclipses, meteor showers, and comets. The Chinese, in the 1st century CE, were the first to build automated instruments to measure celestial objects. The Chinese used a water clock as the timer for these devices, creating the first known clock drive. In the 1670s, Jesuits convinced Chinese astronomers to add Western instruments to the Beijing observatory. Observational activities were limited due to a conflict of interests. The Chinese astronomers’ interests in observations were only in revising the current calendar. The church’s stance against any activities associated with heliocentric ideas, and the Jesuits’ strict adherence to this position, also prevented further contribution.
India’s most notable observatories were constructed in the 18th century under the direction of the Hindu prince Jai Singh. He constructed the largest instruments he could to increase accuracy. One tool he commissioned to be built was an 88- foot-tall sundial. Updating Ulugh Beg’s star data, Singh added 4 degrees, 8 arc minutes to the ecliptic longitudinal measurements to accommodate the earth’s precession for the past 300 years.
Bernard Walther built the first notable European observatory in Nuremberg, Germany, in the mid- 1470s CE. Observational data collected at this observatory noted a slight discrepancy in the Alfonso Tables, the most popular star tables in Europe from 1300-1500.
Galileo is often credited with inventing the telescope, which was in fact created in 1608 by the Danish spectacle maker Hans Lippershey. Galileo, however, was the first, in 1609, to turn the device to the skies, using the invention as an astronomical observational device and making a number of improvements to Lippershey’s model. Galileo’s observations through the telescope changed the study of astronomy. Galileo’s most notable observations include the surface features of Earth’s moon and four of the moons of Jupiter. Galileo noted the surface of Earth’s moon was abundant with mountains and dark spots believed to be large bodies of water, which he named maria, or seas. Galileo also observed the phases of Earth’s moon and those of Venus.
Tycho Brahe’s 16th century observatory, built on the Danish island of Hven, was named Uraniborg and housed a number of instruments used in observations. Brahe is credited with recording the most accurate observational data of his time, prior to the invention of the telescope. Johannes Kepler assisted Brahe, and after Brahe’s death, Kepler used the data gathered by Brahe to create his laws of planetary motion.
The Paris Observatory, built in 1667, became a model for national observatories. National observatories, such as the Paris and Greenwich observatories, were dedicated to gathering observational data for national interests, including improving navigation and calendars. By creating accurate tables of star positions, and with the invention of the chronometer, seafaring vessels were capable of determining their geographical location at sea.
Private observatories were also constructed, usually by wealthy individuals or organizations. In 1781, William Herschel’s discovery of Uranus won favor with King George III, and Herschel was soon appointed as the king’s astronomer. Herschel built his own telescopes, creating them with a high-enough resolution to open the field to galactic astronomy. Inspired by Herschel, Johann Schröter built the largest observatory of its time in Europe in the small town of Lilienthal, Germany. Schröter sketched the surfaces of the moon and of Mars, creating an interest in the studies of planetary astronomy.
Following in the footsteps of early national observatories, younger nations also built their own modern observatories, some shaped by the field of astrophysics. One such nation, the United States, erected the United States Naval Observatory in 1839.
While attending the Massachusetts Institute of Technology, George Hale invented a device known as a spectroheliograph, which is capable of photographing the sun. Hale built a solar observatory in his parents’ backyard, located in a Chicago suburb. Hale accepted a position at the University of Chicago, and the construction of the university’s Yerkes Observatory in Wisconsin was completed in 1897. The Yerkes Observatory was one of the first observatories constructed for the purpose of studying astrophysics rather than average celestial observations. Hale also planned the construction of the Mt. Wilson Observatory in California in 1904.
After the success of the Mt. Wilson Observatory and the Palomar Observatory in California, it was recognized that mountaintop locations near the ocean were ideal for observatories. Most observatories are now constructed upon higher elevations in an attempt to observe above, rather than through, the atmospheric interference. Today, observatories use not only optical telescopes but also radio telescopes and X-ray and gamma-ray telescopes. These telescopes allow us to “see” wavelegths outside of visible light. While radio telescopes can be used on Earth, most X-ray, gamma-ray, infrared, and ultraviolet wavelengths are blocked by the atmosphere and are best observed from space, through spacebased observatories such as the Hubble Space Telescope. Optical telescopes also capture their best images from space, due to the lack of interference from the atmosphere.
Mat T. Wilson
See also Calendar, Gregorian; Calendar, Julian; Galilei, Galileo; Light, Speed of; Planetariums; Sundials; Telescopes
Aveni, A. F. (1977). Native American astronomy. Austin: University of Texas Press.
Heilbron, J. L. (1999). The sun in the church.
Cambridge, MA: Harvard University Press.
North, J., & Porter, R. (1995). Norton history of astronomy and cosmology. New York: Norton.