Astronomy in 1909 : A paradox of knowledge

Among my various fascinations in science is the reading of old textbooks and books for the general public, particularly in Astronomy.  Recently I read Curiosities of the Sky by Garrett Putman Serviss, published in 1909.  This was a fascinating time period for this science – large telescopes were becoming more common, and many of the modern methods of astronomical analysis were becoming widespread. 

The first photograph taken through a telescope of a star had taken place in 1840, and by the turn of the century astrophotography of bright objects was commonplace.  The use of a spectrograph to analyze the chemical composition of gases between a source of light and the observer was discovered in chemistry as far back as the 1700s, but the first spectrograph of a star was obtained in 1863.  Spectroscopy had discovered the element helium first in the Sun (hence its name), and only later was helium found on Earth.

This was also a time for rapid advancement in physics – Einstein had published his papers on special relativity in 1905, and would present his revolutionary general theory of relativity in 1916.  Radioactivity was a newly-discovered phenomenon (1896), and Marie Curie had won her first Noble Prize in 1903, to be followed by a second in 1913.  Atomic physics was well known to be the correct description of the building blocks of matter, though the craziness of the theory of quantum mechanics had not yet been established.  (I am no fan of that theory, though that is a discussion for another day).

With the rise of both of these sciences into their “golden eras”, we see the dawn of a new science – astrophysics – the attempt to explain the nature and processes of the objects we observe in the cosmos.  Reading through this 1909 account, we see the progress of that science at a snapshot in time.  The combination of knowledge and misunderstanding is truly fascinating.

For example, it was known that the planet Mercury was far too hot to support life, and that both Mercury and Venus orbited the Sun with the same side facing the Sun at all times – just as the Moon keeps the same face toward Earth at all times.  (This is actually not true of either planet, but the rotation periods are very slow for both, so the inaccuracy of their measurements is very understandable).  The Moon was known to be lifeless and devoid of water, though the craters were thought to be all volcanic in nature (all lunar craters are now known to be caused by impacts).

Mars was conjectured to be populated by intelligent beings who had built an incredible system of canals to transport water from the polar regions into their population centers.  The Martians were believed to be a very ancient species, far older than mankind, based on some confusing hypothesis that the smallness of the planet (1/3rd the size of Earth) indicated that it was much older than Earth, because it had been shrinking longer.  This seems to be the source of the popular opinion in the early 20th century that the Martians had much more advanced technology than ours.

A great deal was known about the relative distances to the various stars, and their sizes, and even the composition of the stars.  The distances were mostly underestimated, but at least the idea that stars were many light years away (each light year is about 6 trillion miles) had replaced earlier estimates of the stars being only a few 100 million miles distant, and all about the same distance from Earth.

The source of energy for the stars was completely unknown.  As a result, the average lifetime of a star was very greatly underestimated.  Lord Kelvin, as late as 1897, had “proven” that the sun could not have been more than 20 million years old, and that Earth had been habitable for only a few million years and could only last a few million more.  His arguments were based on the assumption that all of the heat in the sun was generated only from the gravitational energy of  the collapsing cloud of gas from which it formed.  It would take the advent of nuclear physics in the 1920s to point us to the correct source of the sun’s energy, and extend its lifetime from millions to billions of years.

A very accurate understanding of one of the most puzzling objects in the sky – comets – had been obtained by 1909.  As late as the 19th century, very little was understood about these objects that appear suddenly, seemingly from nowhere, impress mankind with their brightness and size across the night sky, and then fade away from view, usually never to be seen again.  Kepler, Galileo, and even Newton had only wild conjectures about their nature, with a debate as to whether these objects were in Earth’s atmosphere, or between the Earth and Moon.  But in the 1909 account we hear that these are bodies orbiting the Sun, not unlike the planets and asteroids, and that the tails are formed as frozen gas and dust heat up and are pushed by an influence from the Sun (thought to be light itself, but now known to be a flow of protons) into a tail that points away from the Sun at all times.

But on the other hand, the understanding of what we now know to be galaxies was entirely lacking.  Everything that appeared in the telescope as a blurry dim object was called a “nebula” (or cloud).  The term Universe was used to describe what we now just refer to as the Milky Way galaxy.  The Milky Way was known to be finite in size, but it was assumed that everything that can be seen in a telescope lay within its boundaries. 

The presence of “spiral nebulae”, which are the nearer galaxies that appear face one to us, were used to confirm the theory of Laplace for the formation of the Earth – that a large cloud of gas had slowly collapsed to form the Sun, and had thrown off “shells” of gas and rock that had later formed the planets.  Laplace’s theory was roughly correct; the evidence of the spiral nebulae was, however, completely misunderstood.  A few years after this book was published, Sir Edwin Hubble would discover that these spiral nebula were in fact “other universes”, each consisting of billions of stars, at distances so vast that they would forever appear to us as clouds of dim light.

For the very interested, the book is available for free at www.gutenburg.org, and can be downloaded in a variety of formats, including the Kindle format.  I hope you have enjoyed this discussion of the history of my favorite science.