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Mystery of the starry sphere

Rohit Gupta | Updated on January 23, 2018 Published on October 09, 2015

Too big for the palm: Emperor Jahangir is shown holding a globe in this Mughal-era painting. The globe is believed to have been made by metallurgist Muhammad Salih Tahtawi. Photo: Wikipedia

Rohit Gupta   -  BUSINESS LINE

Astronomers proposed and discarded many fantastical visions of the Earth’s shape and place in the universe before understanding that the universe, as we know it now, would fit in the palm of no earthly emperor

In the largest painting to have emerged from the Mughal period, emperor Jahangir (the name means ‘world-seizer’) is seen holding a globe in his right palm. It is believed that this globe was constructed by the metallurgist Muhammad Salih Tahtawi. He was famed for the impossible feat of constructing seamless hollow spheres, leaving no tell-tale cavity or crease from its making.

Seventeenth century astrolabe makers in Lahore appear to have excelled in this method, called the ‘cire perdue’ (lost wax), a technique which is now lost to history. Emilie Savage-Smith writes in a detailed study that “seamlessly cast globes continued to be made in Lahore up to the mid-19th century. In 1842, Lala Balhumal Lahuri, a Hindu maker of precision instruments made such a globe, inscribed in Arabic and Persian for his Sikh patron.” She adds that “no workshop today, anywhere in the world, knows how to do this and indeed the casting of seamless metal spheres is regarded as technically impossible”.

The purpose of these globes was to create a map of the night sky as it appeared to observers on Earth. Since the planets moved gently through the sky, but the stars remained fixed in their positions every night — it was thought for a long time that they were attached to something solid — like jewels inside a giant hollow sphere. “And we have adorned the nearest heaven with lamps,” says one translation of the Q’uran.

Numerous fantastical visions of Earth’s shape and place in the universe have been proposed and discarded since antiquity. Such as Anaximenes of Miletus (sixth century BC), who held that “the Earth was a cylinder three times as wide as high, and that it was surrounded by three concentric rings carrying the fixed stars, the Moon, and the Sun.” Even when the cylinder was discarded for a sphere, “This system of a spherical Earth surrounded by concentric spheres of water, air, fire, and then the spheres of the heavenly bodies remained the basis for cosmology and physics for the next two millennia.” (Albert van Helden, Measuring the Universe).

As late as 1692, the famous astronomer Edmund Halley erroneously proposed that the Earth was “a hollow shell about 800 km (500 miles) thick, two inner concentric shells and an innermost core, about the diameters of the planets Venus, Mars, and Mercury. Atmospheres separate these shells, and each shell has its own magnetic poles. The spheres rotate at different speeds…”

Great discoveries in astronomy were made despite the fact that these models were utterly wrong. Johannes Kepler found the laws of the planetary orbits even though he believed them to be moving within transparent, crystalline Platonic solids. These nested solids, according to his book Mysterium Cosmographicum (1596), are the scaffold that supports the movement of the orbs, a need which was later dismissed by an understanding of gravity.

Similar models of the solar system came down from the Greeks, and were passed on to the Arabs — who expanded and detailed this worldview. It is through Islamic writers, and not through Kepler — that the idea of solid spheres holding the orbits in place came to India and appears in 17th century Varanasi.

Two astronomers belonging to rival families, who went to war over this theory, are mentioned in Kim Plofker’s Mathematics In India. “The Islamic cosmological notions accepted by Kamalakara’s family or school included the concept of transparent “crystalline” celestial spheres for the physical support and impulsion of the orbiting bodies. Munisvara’s side objected to this idea on the grounds that such a material could not be strong enough for this purpose. If any such spheres existed, they would have to be made of metal, conforming to traditional Indian descriptions of the blue sky as a round metal surface. This debate and related controversies were continued between Kamalakara’s brother and Munisvara’s cousin in two treatises entitled Loha-gola-khandana (“Smashing of the Iron Spheres”) and Loha-gola-samarthana (“Vindication of the Iron Spheres”).”

Unusual here was the discussion about the strength of this material, since aspects of physics are not found often in Indian astronomy. Physically speaking, it could even be pondered whether such a large sphere would not collapse under its own gravity and become a planet itself.

The mystery of the spheres began to finally clear when astronomers such as Christoph Rothmann and Tycho Brahe studied comets that came from outside the solar system. The comet of 1585, observed Rothmann — was beyond Saturn and there was no refraction by any intervening material. The comets were travelling to the Sun completely unhindered by any invisible spheres, right through the planetary orbits — as if nothing at all existed over there, not even glass.

The fixed stars, we know now, are not arrayed like jewels on some finite celestial crown, but scattered like dust in a universe that may be infinitely large — a universe that would fit in the palm of no earthly emperor.

Rohit Gupta explores the history of science as Compasswallah

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Published on October 09, 2015
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