Fjordman: A History of Astrophysics — Part 1

Fjordman has published his latest essay — the first part of a series on astrophysics — at the Brussels Journal. Some excerpts are below:

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 founding. 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 of the Pre-Socratic philosophers to live in Athens. He held 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 Greeks still shared the divine associations with the heavenly bodies, but political considerations may have played a part in this, too.

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 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.

- - - - - - - - -

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, 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.

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 in the sixteenth century AD in Mesoamerica, the region usually credited with having 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. A little over 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 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.

Read the rest at the Brussels Journal.