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This essay was originally published in five parts at various sites: Part 1, Part 2, Part 3, Part 4, and Part 5
The introduction of the telescope in Western Europe in the 1600s revolutionized astronomy, but it did not found it as a discipline. Astronomy had existed in some form for thousands of years prior to this. It is consequently impossible to assign a specific date to its beginning. This is not the case with astrophysics. People in ancient and medieval times might speculate on the material makeup of stars and celestial bodies, but they had no way of verifying their ideas.
Anaxagoras of Clazomenae in the fifth century BC was the first Pre-Socratic philosopher to live in Athens. He championed many controversial theories, including his claim that the stars are fiery stones. He allegedly got this idea when a meteorite fell near Aegospotami. He assumed that it came from the Sun, and since it consisted largely of iron he concluded that the Sun was made of red-hot iron. Not a bad guess for his time, yet he had no way of proving his claims. Neither did Asian or Mesoamerican observers. Some sources indicate that Anaxagoras was charged with impiety, as most ancient Greeks still shared the divine associations with the heavenly bodies, but political considerations may have played a part in this process as well.
As late as in 1835 Auguste Comte (1798-1857), the French philosopher often regarded as the founder of sociology, stated that humans would never be able to understand the composition of stars. He was soon proved wrong by two new techniques — spectroscopy and photography.
The English chemist William Hyde Wollaston (1766-1828) in 1800 formed a partnership with his countryman Smithson Tennant (1761-1815), whom he had befriended at Cambridge. Tennant discovered the elements iridium and osmium, extracted from platinum ores, in 1803. The platinum group metals — platinum, ruthenium, rhodium, palladium, osmium and iridium — have similar chemical properties. Osmium (Os, atomic number 76) is the heaviest natural element with a density of more than 22.6 kg/dm3, twice as much as lead at 11.3 kg/dm3.
Platinum (Pt, atomic number 78) and its dense sister metals are very rare in the Earth’s crust. It had been introduced to Europe from South American mines in the 1740s by men such as the Spanish explorer Antonio de Ulloa (1716-1795). Wollaston was the first person to produce pure, malleable platinum and became wealthy from supplying Britain with the precious metal. The Wollaston Medal, granted by the Geological Society of London, is named after him.
The German chemist Martin Klaproth (1743-1817) was born in Wernigerode in Prussian Saxony and worked as an apothecary for years before continuing his career as a professor of chemistry at the newly established University of Berlin. He discovered uranium as well as zirconium (Zr, a.n. 40) in 1789. Uranium (symbol U, atomic number 92) was named for the planet Uranus, which had been discovered just prior to this. Wollaston detected the elements palladium in 1803 and rhodium in 1804. He named palladium (Pd, a.n. 46) after the asteroid Pallas, which had been discovered a year earlier by the German astronomer Olbers and was initially believed to be a planet, until the full extent of the asteroid belt had been grasped.
The birth of spectroscopy, the systematic study of the interaction of light with matter, followed shortly after the creation of scientific chemistry in Europe. William Hyde Wollaston in 1802 noted some dark features in the solar spectrum, but he didn’t follow this insight up. In 1814, the German physicist Joseph von Fraunhofer (1787-1826) independently discovered these dark features (absorption lines) in the optical spectrum of the Sun, which are now known as Fraunhofer lines. He carefully studied them and noted that they exist in the spectra of Venus and the stars, too, which meant that they had to be a property of the light itself.
In the 1780s a Swiss artisan, Pierre-Louis Guinand (1748-1824), began experimenting with the manufacture of flint glass, and in 1805 managed to produce a nearly flawless material. He passed on this secret to Fraunhofer, who worked in the secularized Benedictine monastery of Benediktbeuern. Fraunhofer improved upon Guinand’s techniques and began a more systematic study of the mysterious spectral lines. To the stronger ones he assigned the letters A to Z, a system which is also used today. Yet it was left to two other German scholars to prove the full significance of these unique lines, corresponding to specific chemical elements.
Robert Bunsen (1811-1899) is often associated with the Bunsen burner, a device found in many chemistry laboratories around the word, but the truth is that he made a few alterations to it rather than inventing it. He was born in Göttingen, where his father was a professor of languages. He obtained his doctorate in chemistry at the University of Göttingen and spent years traveling through Western Europe. He eventually settled at the scenic university town of Heidelberg in south-west Germany, where he taught from 1852 until his retirement. In the late 1850s, Bunsen began a new and very fruitful collaboration there with the physicist Kirchhoff.
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Gustav Kirchhoff (1824-1887), the son of a lawyer, was born and educated in Königsberg, Prussia, on the Baltic Sea, now the Russian city of Kaliningrad. He graduated from Albertus University there in 1847 and relocated to the rapidly growing city of Berlin. After 1850 he became acquainted with Bunsen, who urged him to follow him to Heidelberg. Kirchhoff in 1859 coined the term blackbody to describe a hypothetical perfect radiator that absorbs all incident light and emits all of that light when maintained at a constant temperature. His findings proved instrumental to Max Planck’s quantum theory of electromagnetic radiation from 1900. He is above all remembered for his collaboration with Bunsen around 1860.
They demonstrated in 1859 that all pure substances display a characteristic spectrum. Together, Bunsen and Kirchhoff assembled the flame, prism, lenses and viewing tubes necessary to produce the world’s first spectrometer. They identified the alkali metals cesium (chemical symbol Cs, atomic number 55) and rubidium (Rb, a.n. 37) in 1860-61, showing in each case that these new elements produced line spectra that were unique for them, a chemical “fingerprint.” The dark lines in the solar spectrum show the selective absorption of light, caused by the transition of an electron between specific energy levels in an atom, in the gases of various elements that exist above the Sun’s surface. In the first qualitative chemical analysis of a celestial body, Kirchoff in the 1860s identified 16 different elements from the Sun’s spectrum and compared these to laboratory spectra from known elements here on Earth.
The great physicist George Gabriel Stokes (1819-1903) attended school in Dublin, Ireland, but later moved to England and Cambridge University. He theorized a reasonably correct explanation of the Fraunhofer lines in the solar spectrum, but he did not publish it or develop it further. According to the Molecular Expressions website, “ Throughout his career, George Stokes emphasized the importance of experimentation and problem solving, rather than focusing solely on pure mathematics. His practical approach served him well and he made important advances in several fields, most notably hydrodynamics and optics. Stokes coined the term fluorescence, discovered that fluorescence can be induced in certain substances by stimulation with ultraviolet light, and formulated Stokes Law in 1852. Sometimes referred to as Stokes shift, the law holds that the wavelength of fluorescent light is always greater than the wavelength of the exciting light. An advocate of the wave theory of light, Stokes was one of the prominent nineteenth century scientists that believed in the concept of an ether permeating space, which he supposed was necessary for light waves to travel.”
Fluorescence microscopy has become an important tool in cellular biology. The Polish physicist Alexander Jablonski (1898-1980) at the University of Warsaw was a pioneer in fluorescence spectroscopy. Stokes was a formative influence on subsequent generations of Cambridge men and was one of the great names among nineteenth century mathematical physics, which included Michael Faraday, James Joule, Siméon Poisson, Augustin Cauchy and Joseph Fourier. The English mathematician George Green (1793-1841), known for Green’s Theorem, inspired Lord Kelvin and devised an early theory of electricity and magnetism that formed some of the basis for the work of scientists like James Clerk Maxwell.
Astrophysics as a scientific discipline was born in mid-nineteenth century Europe, and only there; it could not have happened earlier as the crucial combination of chemical and optical knowledge, telescopes and photography did not exist before. In case we forget what a huge step this was, let us recall that as late as the sixteenth century AD in Mesoamerica, the region with the most sophisticated American astronomical traditions, thousands of people had their hearts ripped out every year to please the gods and ensure that the Sun would keep on shining.
Merely three centuries later, European scholars could empirically study the composition of the Sun and verify that it was essentially made of the same stuff as the Earth, only much hotter. Within the next few generations, European and Western scholars would in less than a century proceed to explain how the Sun and the stars generate their energy and why they shine. By any yardstick, this represents one of the greatest triumphs of the human mind in history.
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