SPHERES OF THE HEAVENS - Celestial Globes

Celestial Globe, Isfahan (?), Iran 1144. Shown at the Louvre Museum, this globe is the 3rd oldest surviving in the world

Giuseppe de Rossi Celestial globe, Venice, Museo Correr

Long before there were planetariums or advanced technologies available for studying the sky, people devised ways of depicting the sun, moon, planets, and stars in relation to the Earth. There was a desire to learn about astronomical history and events; people wanted to figure out how Earth fit into the grand scheme of the universe. Globes helped to put objects into perspective, and served as scientific instruments, ornamental showpieces, and physical illustrations of the astronomy beliefs of the day.

Globes have been visual representations of the physical characteristics of Earth and Sky for thousands of years

Celestial Globe at The Franklin Institute

. Generally, there are three types of globes. Terrestrial globes detail geographical features of the Earth. There are also globes that illustrate the physical features of celestial bodies, such as the moon or Mars. Celestial globes, like the one pictured here, are spherical maps of the sky—models of the visible heavens.

There is written evidence that proves that the ancient world was familiar with the scientific principles necessary for depicting the celestial and terrestrial spheres, and the oldest known surviving ancient globe is the Farnese Atlas, now at the National Museum of Naples. The Farnese Atlas is a decorative celestial globe, about 25 inches in diameter, that shows the outline of constellations against a coordinate system. The statue of Atlas is dated 73 B.C.; the position of the constellation figures to the globe's equinox date the globe itself to around 370 B.C. (Naturally, the ancient globes and models were representative of the astronomical ideas held at that period of time.)

Astronomy is one of the longest-studied sciences in history. Scientists have attempted to answer questions that seem far beyond our understanding for centuries. As long as we wonder about heavenly objects, some will try to recreate the nighttime sky with instruments such as the globe, lighting the world as the stars themselves do with their ideas, models, and theories.

Reference: Instruments of Science: An Historical Encyclopedia New York & London, 1998.

Construction of an Astrolabe

Astrolabe of Jean Fusoris (fr), made in Paris, 1400

An astrolabe consists of a disk, called the mater (mother), which is deep enough to hold one or more flat plates called tympans, or climates. A tympan is made for a specific latitude and is engraved with a stereographic projection of circles denoting azimuth and altitude and representing the portion of the celestial sphere above the local horizon. The rim of the mater is typically graduated into hours of time, degrees of arc, or both. Above the mater and tympan, the rete, a framework bearing a projection of the ecliptic plane and several pointers indicating the positions of the brightest stars, is free to rotate. These pointers are often just simple points, but depending on the skill of the craftsman can be very elaborate and artistic. There are examples of astrolabes with artistic pointers in the shape of balls, stars, snakes, hands, dogs' heads, and leaves, among others.[28] Some astrolabes have a narrow rule or label which rotates over the rete, and may be marked with a scale of declinations.

The rete, representing the sky, functions as a star chart. When it is rotated, the stars and the ecliptic move over the projection of the coordinates on the tympan. One complete rotation corresponds to the passage of a day. The astrolabe is therefore a predecessor of the modern planisphere.

On the back of the mater there is often engraved a number of scales that are useful in the astrolabe's various applications; these vary from designer to designer, but might include curves for time conversions, a calendar for converting the day of the month to the sun's position on the ecliptic, trigonometric scales, and a graduation of 360 degrees around the back edge. The alidade is attached to the back face. An alidade can be seen in the lower right illustration of the Persian astrolabe above. When the astrolabe is held vertically, the alidade can be rotated and the sun or a star sighted along its length, so that its altitude in degrees can be read ("taken") from the graduated edge of the astrolabe; hence the word's Greek roots: "astron" (ἄστρον) = star + "lab-" (λαβ-) = to take.

The Astrolabe, East and West

Astrolabes were used in cultures rooted in religious faith and they reflect the sacred character of the cosmos. Examples from Christendom may have calendars with saints' days, and times of prayer were important for Christians and Muslims, but it was in Islam that the astrolabe was particularly adapted to religious observance. It could be used to find the five times of daily prayer and the sacred direction or 'Qibla', so that the faithful could face towards Mecca in prayer. The astrolabe's traditional role in religious observance may explain why it continued to be made and used much later in Islam than in the West. 

Gift to a mosque

An inscription on the back tells us that this instrument was a gift to a mosque in Fez. Inside the mater is a perpetual calendar for the Muslim and Christian years.

Astrolabe, by Muhammad ibn Ahmad al-Battuti, North African, 1733/4 (Inv. 51459)

An inscription on the back tells us that this instrument was a gift to a mosque in Fez. Inside the mater is a perpetual calendar for the Muslim and Christian years.

Times of prayer
 
Curved lines in the top right quadrant of the back of this astrolabe give the times for the beginning and end of the afternoon prayer in the Muslim observance. Inside the mater (not shown) is a gazetteer of the longitude and latitude of 77 places.

Astrolabe, by Muhammad Muqim, Lahore, c.1650 (Inv. 37530)

Astrolabe, by Muhammad Muqim, Lahore, c.1650 (Inv. 37530)

Ancient Navigation: Astrolabe, by Muhammad Mahdi al-khadim al-Yazdi

This astrolabe, by Muhammad Mahdi, is a masterpiece of Safavid metalwork. The profusion of Persian and Arabic inscriptions confer on it a unique semantic character and the dedication on the throne to an important political personality of the Safavid empire confirm its courtly origin.

Astrolabe, by Muhammad Mahdi al-khadim al-Yazdi, Persian, c.1650

The throne, cast in one piece with the mater and rim, is high and triangular in shape and has an elaborately and delicately pierced base. Both sides bear inscriptions to Safi Quli Beg, an Emir at the court of Shah 'Abbas II.

Both sides of this astrolabe have a verse from the Koran and a Shiite invocation around the edge. The inscription in the throne begins "God: there is no god but Him, the Ever Living, the Ever Watchful. Neither slumber nor sleep overtakes Him. All that is in the heavens and in the earth belongs to Him." Inside the mater is a table for finding the direction of Mecca. 

Astrolabe {star- taker} Elaborate inclinomer, by Muhammad Mahdi al-Yazdi, Persian, c. 1660.

The astrolabe represents a mathematical likeness of the heavens and its Greek name is - "Star Taker". This amazing sophisticated scientific instrument has been crafted by Muhammad Mahdi al-Khadim al-Yazdi in brass and was used to solve astronomical problems and to show the positions of stars and planets at different dates, times and latitudes. The Persian calligraphy engraving reads a quotation from the Koran: "The world is decorated with stars".

Ancient Navigation: Sextant

With the sextant for determining latitude and the chronometer for longitude, sailors by the 1800s were able to navigate the high seas with great precision. Photo credit: © Bruno Buongiorno Nardelli/iStockphoto.com

For millennia, as sailors from the Phoenicians to the Polynesians knew, the heavens remained the best way to find one's north-south position. Increasingly sophisticated devices were designed over the centuries to measure the height of the sun and stars over the horizon. The gnomon or sun-shadow disk operated like a sundial, enabling the user to determine his latitude by the length of the sun's shadow cast on a disk floating level in water. The Arabian kamal was a rectangular plate that one moved closer or farther from one's face until the distance between the North star and the horizon exactly corresponded to the plate's upper and lower edges. The distance the plate lay away from the face—measured by a string tied to the center of the plate and held at the other end to the tip of the nose—determined the latitude.

In the Middle Ages, sailors relied on the astrolabe, a disc of metal that one held suspended by a small ring. The disc had a scale with degrees and a ruler for measuring the height of an astronomical body. Other medieval mariners preferred the cross-staff, a T-shaped device whose base was held up to the eye. One measured the sun's height by pulling the slidable top of the T toward one's eye until the sun lay at the top and the horizon at the bottom. Since blindness resulted from frequent use, the explorer John Davis invented the back-staff in 1595, which enabled one to get the same measurement with one's back to the sun. The sextant was the most advanced of these devices, allowing users to determine their latitude to within a sea mile or two, even from a swaying deck.

In the years after the sextant was invented in 1731, many held out hope that it would aid in east-west navigation as well—that is, in finding longitude. Sailors could employ the sextant to figure longitude using the lunar-distance method, but with the astronomical tables of the 18th century, the process could take several hours to work out one's position—not remotely good enough for sea travel. In the end, it was the dogged clockmaker, John Harrison, who solved the longitude problem with his chronometers. And today, the precocious step-child of these highly accurate clocks, the Global Positioning System, has finally proved the Roman dramatist Seneca right, when he wrote in the first century:

 There will come an age in the far-off years
When Ocean shall unloose the bonds of things,
When the whole broad earth shall be revealed....

Read More

Deepest Roman shipwrecks found near Greece - and prove that ancient seafarers were more adventurous than thought ...

Two Roman-era shipwrecks have been found in deep water off a western Greek island, challenging the idea that ancient ship masters stuck to coastal routes.

The merchant ships were sunk nearly a mile deep between Corfu and Italy moving that ancient traders didn't 'hug the shore'. 

Greece's culture ministry said the two third-century wrecks were discovered earlier this month during a survey of an area where a Greek-Italian gas pipeline is to be sunk.

Broken ancient pottery from the 3rd Century AD ship: The merchant ships were sunk nearly a mile deep between Corfu and Italy - proving that ancient traders didn't 'hug the shore'

‘The conventional theory was that, as these were small vessels up to 80 feet long, they did not have the capacity to navigate far from the coast, so that if there was a wreck they would be close enough to the coast to save the crew,’ she said. 

U.S. archaeologist Brendan Foley, who was not involved in the project, said a series of ancient wrecks located far from land over the past 15 years has forced experts to reconsider the coast-hugging theory.

They lay between 0.7-0.9 miles deep in the sea between Corfu and Italy.

That would place them among the deepest known ancient wrecks in the Mediterranean, apart from remains found in 1999 of an older vessel some 3 kilometers 1.8 miles deep off Cyprus.

Angeliki Simossi, head of Greece's underwater antiquities department, said sunken ancient ships are generally found 100-130 feet deep.

Most scholars believe that ancient traders were unwilling to veer far offshore, unlike warships which were unburdened by ballast and cargo.

The ships, from the 3rd Century AD, prove that merchant craft of the era didn't 'hug the shore' and sailed across deep water instead

The remains were located during an investigation that covered 200 square kilometers (77 square miles) of seabed off the islands of Corfu and Paxoi.

A Greek oceanographic vessel using side-scan radar and robot submarines took footage of scattered cargo - storage jars, or amphorae, used to carry foodstuffs and wine - cooking utensils for the crew, anchors, ballast stones and what could be remains of the wooden ships.

The team also raised samples of pottery and a marble vase.

The one ship was carrying the kind of amphorae produced in north Africa, and Simossi said it might have sailed from there and headed for Greece after a stop in Italy.

Foley said deep wrecks are very important because they are almost always more intact than those found in shallow water.

‘So they contain far more archaeological and historical information than other sites,’ he said in an email. ‘As a result, the deep sea floor of the Mediterranean is the world's greatest repository for information about the earliest civilizations.’


Read more at the Daily Mail