Chad Orzel

Thanks to Netgalley and BenBella Books for providing an advance copy in exchange for an honest review.

I'm a self-confessed sucker for books titled "A Brief History of.." although my track record of fully understanding the treated topic ranges from fairly appreciable to almost negligible. The latter proved the case when I attempted to read "A Brief History of Time" by Stephen Hawking exactly 25 years ago. With this in mind and in view of the near identical title, it was with slight trepidation that I started out on "A Brief History of Timekeeping" by Chad Orzel. It proved to be a tremendously enjoyable read providing a broader treatment of the topic than I'd initially expected. The evolution of humanity's endeavour to observe and track time is intimately intertwined with the concomitant development of science through the ages. The evolution of science led to ever more precise ways of timekeeping and more precise timekeeping in turn aided the evolution of science. This book tracks the development of the concept of time, which was initially based on the asynchronous rotations of the sun and/or the moon. The corrective modifications each method's imprecisions constantly required were initially solved when timekeeping was divorced from the heavenly bodies and brought down to earth on the influences of Newtonian physics. The birth of Einstein's special and general theories of relativity lead to ever more precise methods of measuring the singular ticking of the concept of time. This book proved to be a wonderful journey through the history of science behind timekeeping and ended with a glance into the future.

I must admit that the astronomy and physics at times can seem a bit overpowering, unless you tackle the characteristics of cesium atoms, and general and special relativity on a frequent basis. Even though all topics are fairly clearly explained and illustrated (or can be glossed over as you get to the general idea of the matter), I think a basic understanding of physics is definitely helpful when tackling this book.

#ABriefHistoryofTimekeeping #NetGalley… (plus d'informations)

Although much of this history is well known, Orzel tells it well, and there are enough good details to make it a worthwhile read.

> The initial introduction of the Julian system required one “ultimus annus confusionis” to bring the calendar back into synch with the seasons: this “final year of confusion” (46 BCE in the modern system) ran to an amazing 445 days. The Julian calendar was officially introduced in 45 BCE, and after a small correction to the leap year implementation under the emperor Augustus in 8 BCE, it was the official calendar for the remainder of the Roman empire and into the post-Roman era of Europe

> the Islamic calendar gives highest priority to the phases of the moon, allowing the months of the year to drift through the seasons. The Julian calendar (immediate ancestor of the modern Gregorian civil calendar) gives the highest priority to the seasons of the year, ensuring that spring and summer always start in the same months, but losing any direct connection to the phases of the moon. The Hebrew calendar represents an attempt to strike a balance between the two, ensuring that the holy days always fall at the appropriate point in the lunar cycle, but inserting the occasional month to keep them in the right general season as well.

> The year 2030 is an interesting example of a Gregorian year in which Ramadan will start twice, first in January and again in late December.

> the months of Quintilius and Sextilius were renamed in honor of the Caesars, the origin of the modern names “July” and “August”; February was also shortened by another day to ensure that Augustus’s month was the same length as Julius’s

> a “lost” period of 11 days. In 1752 in the United Kingdom, September 2 was by decree of Parliament followed by September 14. … The dropping of 11 days was required to bring Britain (and its colonies) into synchrony with the Gregorian calendar that had already been in use in continental Europe for a century and a half.

> In 1517, a German monk named Martin Luther published his 95 Theses, a list of grievances about corrupt practices within the Catholic Church … Luther’s writings kicked off the Protestant Reformation that splintered the Catholic Church into the wide range of Christian denominations we have today, and it was the trigger for more than a century of sectarian warfare. In response to Luther and other reformers, the Catholic Church launched a “Counter-Reformation” to clarify and formalize Catholic doctrine. The centerpiece of this effort was the Council of Trent, formally convened by Pope Paul III in late 1545. Thirty-seven years and six popes later, this led to the adoption of the modern Gregorian calendar. … After he took office as Pope Gregory XIII in 1572, he decided to settle the calendar issue once and for all.

> This shift was accomplished by the same technique later used in Britain: dropping 10 days from the calendar for one year. Thursday, October 4, 1582, was followed by Friday, October 15, with the specific dates to be skipped chosen because no significant feasts or saints’ days fell in that span. … The calendar reform was announced in the papal bull “Inter gravissimus,” dated February 24, 1582, ordering its implementation that fall.

> Experiments with models made from plaster casts of the original suggest that the Karnak clepsydra worked very well at its (presumed) function of dividing the night into equal hours. As an additional refinement, the Karnak clepsydra features not just one hourly scale, but 12, each headed with the name of a month in the Egyptian civil calendar. The spacing between hour marks on these scales varies in a way that tracks the changing length of the night across the seasons. The careful shaping of the Karnak clepsydra is a significant accomplishment for the scientists and engineers of 1500 BCE, fully justifying Amenemhet’s posthumous pride in his invention. There’s a simpler way to ensure a constant rate of water flow, though, namely by keeping the level of the liquid constant. Of course, this can’t be used in an outflow-type clock (by definition), so it requires a transition to an inflow-type water clock

> The two periods of visibility, in the morning and evening, are roughly equal in length, but the two periods when Venus is lost in the glare of the sun have very different lengths. When the two planets are on opposite sides of the sun (“superior conjunction” in astronomy jargon), both planets are moving in a direction that tends to keep the sun between them, like two people in a slapstick comedy chasing each other around a table. Venus’s faster motion eventually makes it pull ahead, but the period in which it’s hidden lasts several weeks. When they’re on the same side of the sun (“inferior conjunction”), Venus’s faster orbit takes it away from the sun in a matter of a few days. This is why the time between Venus’s disappearance from the morning sky and its reappearance in the evening lasts 50 days (90 in the Dresden Codex tables), but its disappearance from the evening sky and return in the morning lasts only eight days.

> The lack of parallax for the new star showed that it was very distant from the earth, much more distant than the moon, which showed observable parallax. This was a clear problem for the Aristotelian worldview, which divided the universe into a variety of spherical zones associated with the various celestial objects located in them. The most distant sphere, containing the fixed stars, was held to be perfect and unchanging, with more transient effects like meteors and comets being essentially atmospheric phenomena confined to the “sublunar” region between the earth and the moon. Tycho’s parallax measurements placed the new star well outside that zone, and thus posed a philosophical problem. … His most famous instrument was the huge mural quadrant, essentially a circular arc a bit under two meters in radius painted on a north-south wall with markings for angles from 0 to 90 degrees (one-fourth of a circle, thus “quadrant”). The observer would move around to sight the object of interest as it crossed the north-south meridian, reading the declination off directly and determining the right ascension from the time (measured by water clocks in the observatory; in Tycho’s heyday, mechanical clocks weren’t up to the level of precision he demanded).

> The better known of the two was from the English clockmaker John Harrison, who developed a mechanical watch that could keep time at sea. The other large award handed out by the Board of Longitude was a posthumous £3,000 to German mathematician Tobias Mayer for a set of tables predicting the position of the moon with sufficient accuracy for navigational purposes. Mayer is far less celebrated than Harrison, but his method was in many ways the more immediately successful of the two, as his tables formed the basis of the Nautical Almanac that was distributed to ships by the British government and remained an essential navigational resource for a century and a half.

> In the third book, De mundi systemate (“On the System of the World”), Newton turned to detailed applications of the principles set forth in the first two, and compared them directly to observational data. A considerable amount of this book was devoted to exploring the orbit of the moon: Newton laid out the basic idea of the three-body interactions between the sun, the earth, and the moon, and showed how the changing magnitude and direction of the sun’s gravity on the moon can give rise to some of the observed perturbations of the lunar orbit. The quantitative calculation, though, does not work out as well as he might have liked: while Newton had the basic conceptual picture of how the force from the sun causes the apsidal precession of the moon’s orbit, his calculation of the rate of precession was half as big as that observed.

> The regular swinging of a pendulum depends on the downward pull of gravity, but on the deck of a wave-rocked ship, the exact orientation of the clock changes constantly, introducing errors in the rate of ticking. Effectively, the rocking introduces extra “circular error,” because each time the pendulum reaches its turning point, it’s at a different angle from the true vertical. Even if this could be countered, a seagoing pendulum clock must also contend with the problem discovered by Richer in Cayenne: the strength of gravity is different at different latitudes, changing the period of a pendulum by enough to introduce errors of a few minutes per day. This manifested as an apparent eastward shift in longitudes measured on the 1687 voyage of Huygens’s marine clock, which ticked slower as it approached the equator.

> In the mid-1860s, the best astronomical determinations of the longitude difference between Europe and North America disagreed with each other, and with measurements based on transporting high-quality chronometers back and forth across the Atlantic, by around four seconds. While that seems tiny compared to the issues that faced navigators in John Harrison’s day, it was embarrassingly huge compared to the precision obtained on land using time signals sent by telegraph. The discrepancy was resolved in 1867, using signals sent between Newfoundland and Ireland on one of the first reliable transatlantic cables.… (plus d'informations)