[We don’t spend enough time staring at the night sky. We’re missing a lot. Tonight, go out and find the Big Dipper. Imagine a stick extending from the bottom two points in the cup and follow the line to the brightest star. That’s Polaris, the North Star. It won’t tell you exactly where you are on the planet, but it’s a good start. SB SM]
The History of Astronomy: A Very Short Introduction
by Michael Hoskin
Josh Friedlander‘s review
Reading about the history of astronomy really brings home that we are living in Baudrillard’s world. At most times in human history, the celestial bodies were a fascinating and mysterious puzzle, their movements only roughly predictable, their shape and origins unknown. Time, dates and navigation were the province of experts who relied on precalculated tables.
Today, the situation is reversed: at any moment I can see which stars, planets or comets are visible from my location, and powerful telescopes like the James Webb broadcast images from the origin of time. My microwave keeps perfect time. Yet the night sky is almost entirely blank, hidden by endless streetlights and shop windows. In this hyperreality, only the symbol remains, the liquid crystal signifying a vanished world.
Astronomy began with the ancient Babylonians, and the astrolabe was known to the Greeks. Christianity and Islam created new demands for accuracy, notably the date of Easter (the Sunday after a full moon after the vernal equinox) and times and directions of Islamic prayer.
Copernicus was probably not the first person ever to suggest a heliocentric model of the solar system, but it was a blindingly original idea, going against the Aristotelian consensus. A student added a preface stating (erroneously) that this was just a convenience for calculation, not a physical model. Tycho Brahe, a Danish nobleman, built the first observatory, creating a dataset of unprecedented accuracy. He also detected that stars can appear (novas) and that existing ones can change position (even relative to the celestial background, which moves with earth’s rotation). But soon afterward the telescope was invented and Galileo was one of the first to build one and look through it. For the first time he saw the rough, pitted surface of the moon. He wrote a famous book justifying the Copernican system leading a Dominican priest to one of history’s great puns: “Ye men of Galilee, why stand ye gazing up into heaven” (Acts 1:11).
Johannes Keppler laid down some of the mathematical groundwork behind this system, although he also sought a non-existent symmetry. He designed a geometrical model in which each of the six planets is bound by one of the Platonic solids. With René Descartes, one of the most brilliant and fearless minds of the modern era, astronomy began to merge with physics, and the inherited mistakes of Aristotle were definitively left behind. Newton’s Principia – big chunks of which are given to rejecting Descartes – laid out the force of gravity and the inverse square law of attraction. This also explained the mysterious “precession of the equinox” noted in antiquity: the slight drift each year in the location of the earth, caused by a shift in the elliptical path by which the earth orbits the sun.
Long-distance marine navigation required knowing one’s precise longitude. Britain’s Longitude Act of 1714 offered great riches to anyone who could solve it. After lots of ideas were rejected, two serious ones remained: tables of the relative location of the moon from various places at sea; and a sufficiently accurate chronometer to enable measuring time at sea. Both were accomplished, and John Harrison’s original device can still be seen at the maritime museum in Greenwich.
As science advanced, astronomy gradually became part of physics. Important work is done today by large teams using expensive equipment and often clusters of powerful computers. But it still is accessible to anyone with a sense of wonder, pondering why, if there are infinitely many stars, the sky is not always light (Olber’s paradox), or why we do not feel the earth’s motion. (My daughter asked me this recently, and the answer appears to be that constant motion feels the same as standing still – only change in velocity is detectable.)