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The oldest known lens was found in the ruins of ancient Nineveh and was made of polished rock crystal, an inch and one-half in diameter. Aristophanes in "The Clouds" refers to a glass for burning holes in parchment and also mentions the use of burning glasses for erasing writing from wax tablets. According to Pliny, physicians used them for cauterizing wounds.

Around1000 A. D. the reading stone, what we know as a magnifying glass, was developed. It was a segment of a glass sphere that could be laid against reading material to magnify the letters. It enabled presbyopic monks to read and was probably the first reading aid. The Venetians learned how to produce glass for reading stones, and later they constructed lenses that could be held in a frame in front of the eyes instead of directly on the reading material.

The Chinese are sometimes given credit for developing spectacles about 2000 years ago

The first spectacles had quartz lenses because optical glass had not been developed.

The first recorded example of astronomy is around 3,500 years old and comes from Mesopotamia. Babylonian writings and star charts mapped out the sky, as well as making constant reference to the names of stars given to them by the Sumerians, suggests these people were probably observing the night sky back in the early Bronze Age.

Confirmation of the earliest astronomers is tricky to find, as we believe that people have always studied the sky in one way or another. Archaeologists have found solar observatories from 5,000BCE built in central Europe. These henges are designed to line up with the position of the Sun and sometimes the Moon at various times of the year, usually the seasonal solstices.

The Akkadians are among the first people credited to have kept astronomical records, and the earliest date from around 2500 B.C. They lived in the northern part of what was later called Babylon. The astronomer-priests that lived later in Babylon were able to use the records of the Akkadians to predict some of the motions of the sun, Earth's moon, and stars.

The Egyptians were one of the first to create an accurate calendar. Unlike most cultures', their calendar was based upon the sun and stars rather than on the moon. This was due to the Nile River. With a calendar, they were able to make accurate estimates of when to plant crops, and when the Nile's annual flooding would occur. Since the first calendars, there have always been seven days in a week, to match the quarter cycles of the Moon, and always twelve months in a year, to match the twelve complete cycles of the Moon per year.

Besides the calendar, Egyptians used astronomy to help build some of the most impressive architecture on Earth: The Pyramids. By using knowledge of the sun and constellations, Egyptians were able to align the pyramids and shafts within the pyramids with the cardinal directions, as well as with star groupings that held spiritual significance.

The Chinese have been observing the sky for several millennia, making them the oldest civilization with a continuous astronomical record. Some of the amazing records that the Chinese hold is the first documented solar eclipse - over 4000 years ago in 2136 B.C. The first recording of any planetary grouping was made by the Chinese in 500 B.C. In the 400's B.C. they made the Book of Silk, the earliest known atlas of comets, and it was discovered in a tomb in 1973.

One of the most important - and infamous - contributions of the Greeks was the geocentric model of the universe. The geocentric model means that the Earth, "geo," is at the center, "centric," of the universe, and that all other bodies move around it with the Earth at a fixed location. This idea was based upon the teachings of Aristotle (384-322 B.C.).

This view held so much sway because of many of the philosophies of the ancient Greeks, including Pythagoras and the Pythagoreans. They believed that the circle is the perfect form, and that the simplest model that made sense must be the correct one. Since the heavens were perfect, everything must move upon a circle, and since the simplest model was that the Earth stood still and everything moved around it, then that must also be true. After all, we can't feel the Earth moving, so why should be believe that it does without any extraordinary evidence?

However, evidence against this system was obvious even to the Greeks 2500 years ago. It had to do with the motion of the planets. For periods of time, the planets seem to orbit in an eastward direction across the stars. However, for brief periods of time, they switch and go in a westward direction. This is called retrograde.

The explanation for this now is simple, and is discussed in the Scientific Revolution section. However, back then, philosophers added extra little circles to the orbits of the planets. The planets now orbited on a little circle, whose center orbited on the larger circle that was around the Earth. This circle upon a circle was called an "epicycle," and the larger circle was called a "deferent."

PtolemyThe Greek Aristarchus of Samos (310-230 B.C.) was one of the first to actually present the heliocentric - sun-centered - model of the solar system. However, Aristotle's views were too wide-spread and well-known, and he had too many followers for anyone to listen to an idea that didn't put our egotistical race at the center of the universe.

Around A.D. 140, the Greek astronomer Ptolemy (left) solidified the geocentric model, elaborating and formalizing the view in a manner that closely approximated the movements of the sun and planets. In Ptolemy's model of the universe, Earth was the center sphere, surrounded by eight other spheres, which were, in order, the moon, Mercury, Venus, the sun, Mars, Jupiter, Saturn, and then the "fixed stars."

Every major civilization had their own type of calendar: China, India, and Rome, just to name a few. Most were based upon the cycle of the moon (about every 27.3 days); many days were skipped from our 365-day year. In Ancient Rome, if the calendar was too far off (judging by the seasons), the Emperor at the time would declare that the next day would be "x" days sooner or later than normal (e.g. if today was July 12, tomorrow might be August 2).

Some calendars based upon the rotation of stars. For example, the Ancient Egyptians used the movements of Sirius (AKA The Dog Star) to tell when the floods of the Nile would come.

Persian astronomer Abd al-Rahman al-Sufi (903-986), known as Azophi to Westerners, made the first known observation of a group of stars outside of the Milky Way, the Andromeda galaxy.

The manufacture and properties of lenses were known since the time of the Greeks. Islamic scholars such as the Egyptian physician Alhazen (born in the 10th century) made important contributions to the study of optics. However, lenses were not introduced to Europe until around the 13th century.

Early astronomers used many kinds of instruments to study the heavens. All were basically tools for measuring or calculating the positions of objects in the sky. With them astronomers mapped the stars and made tables to predict the future positions of the Sun, Moon, and planets. This knowledge was important, for the sky served as a clock, a calendar, and a navigational aid to help seafarers find their way. It was used by priests to set the time for religious observances and by astrologers to cast horoscopes.

The ancient Greeks learned to make precise instruments, crowned by the ingenious astrolabe. This hand-held device had a moveable arm to measure the angle of a bright star above the horizon — the star's "altitude." Rotating a metal map of stars to match engraved curves, the user could determine time and direction, locate stars in the sky, determine when the sun would rise or set, and make other calculations. Astrolabes reached their standard configuration by the fourth century, having been first developed in the first or second century near the Egyptian city of Alexandria.

The example shown here is Islamic and dates from the 11th century. Astrolabes were especially important to Muslims who used them to determine the proper hours for prayer and the direction of Mecca. This astrolabe has several interchangeable plates, each engraved with the celestial coordinates for a different latitude. The pointers on the top plate indicate the positions of twenty-two bright stars. The top plate can rotate to show where those stars will appear at different times or dates, much like a modern paper or plastic star finder. The instrument could also be used to predict when the Sun or certain bright stars would rise or set on any date.

Islamic astronomers made careful observations to improve Ptolemy's planetary and stellar positions. Notable observatories include those at Maragha, in north-west Persia (Iran), constructed in 1259 and staffed with renowned astronomers who came from as far as China and Spain, and at Samarkand in central Asia, built around 1420. The bigger such a structure was, the more accurately an observer could measure the positions of planets and stars.

The earliest devices for "sighting the stars" were crude sticks. Seamen improved these, arriving at a quarter-circle ("quadrant") marked off in degrees, with a sighting arm to measure a star's altitude. Eventually the quadrant was replaced by the sextant (named after one-sixth of a circle, it is actually one-twelfth, doubled with the aid of a mirror). A sextant was the inseparable companion of every navigator until the invention of electronic positioning systems in the late 20th century. Astronomers also used quadrants to map the positions of stars and planets.

The larger the naked-eye instrument, the more precisely it could measure angles. A mural ("wall") quadrant was a large 90-degree arc attached to a north-south wall, with a sighting tool to measure the altitudes of stars and planets.

The most famous mural quadrant in Europe was built by Tycho Brahe in the 16th century as part of a grand observatory supported by the King of Denmark. In this picture, an observer at far right slides a sighting device to line up with a star that he sees through a slot in the opposite wall. At the moment the star is seen due south, he announces its altitude angle. An assistant below him announces the time, and another assistant, sitting at left, writes down the numbers. Behind the quadrant is a painting of Tycho and his assistants at work elsewhere in the observatory.

With his mural quadrant and other naked-eye instruments, Tycho recorded the positions of hundreds of stars and followed the motions of planets over decades. His mass of data was invaluable for later astronomers. Tycho's measurements were the most accurate ever made until telescopes came on the scene.


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