Volunteers at Distributed Proofreaders dedicate their efforts to “Preserving history one page at a time.” On rare occasions while working on a text, one encounters a sudden, remarkable, almost palpable connection to the author’s era.
On June 8, 2004, the sun, Venus, and the earth lined up for a few brief hours. Venus, looking like a perfectly round but otherwise undistinguished sunspot, passed across the face of the sun. Such planetary syzygies, results of the clockwork motion of the inner planets, can be predicted with great accuracy, and for centuries into the future.
In his 1916 book “An Introduction to Astronomy”, published by Project Gutenberg on April 24, 2010, the American mathematician and astronomer Forest Ray Moulton wrote,
The transits of Venus, which occur in June and December, are even more infrequent than those of Mercury. The transits of Venus occur in cycles whose intervals are, starting with a June transit, 8, 105.5, 8, and 112.5 years. The last two transits of Venus occurred on December 8, 1874, and on December 6, 1882. The next two will occur on June 8, 2004, and on June 5, 2012.
If Moulton’s book were to be updated a couple of years hence, the same passage would read:
The last two transits of Venus occurred on June 8, 2004, and on June 5–6, 2012. The next two will occur on December 10-11, 2117, and on December 8, 2125.
Almost a century ago, Moulton’s words must have borne the same force of prognostication, confidently predicting events no contemporaneous reader would be alive to witness. To the retrospect of a modern reader, Moulton’s words bridge the decades–and intervening scientific and technological revolutions–from Moulton’s era to our own.
Today, “An Introduction to Astronomy” is an engagingly readable textbook of elementary astronomy, full of current information on geography, motions of the earth and moon, and star maps; incomplete but largely accurate data on the planets and their larger satellites; and poignantly naive descriptions of the “spiral nebulae”, now known to be galaxies in their own right–as numerous as the stars in our own galaxy and inconceivably remote. Pluto had not been discovered, so ironically Moulton’s planetary count, eight, agrees with the modern one.
In these days of interplanetary probes, space-based telescopes, digital data acquisition, and computer-enhanced images, it is easy to forget how recently astronomers’ knowledge was constrained by the limitations of ground-based, visible-light instruments–refracting and reflecting telescopes–and yet how detailed was their knowledge of the solar system and the cosmos beyond. Moulton’s “An Introduction to Astronomy” is a look back to the cosmology of the early 20th Century: Not a dead history, but a book of living information, and a thread of human connection to the science of decades past.
This review was contributed by DP-volunteer adhere.