The Mandate of Heaven:
Astronomy in Ancient China

by Daniele L. R. Marini
Springer, 2026, 485 pages
reviewed by T. Nelson

We keep hearing about how the ancient Chinese developed astronomy before the West. For instance, the Chinese were the only ones who noticed the Crab Supernova, which exploded in 1054 to produce the famous Crab Nebula. They also cataloged many comets and sunspots that Westerners missed, having first documented sunspots in 28 BC.

But as this book shows, they didn’t do much with the knowledge. Chinese astronomy itself covers only 110 pages, most of which consists of brief biographies of Chinese astronomers. Their attention to comets and sunspots reflected how astronomical knowledge was used in China. Unlike the Greeks, who tried to develop abstract mathematical rules to understand the Universe, the Chinese mainly used it for agricultural and traditional seasonal rituals. They never developed any orbital theory or made geometrical calculations. Their predictions of eclipses were far less accurate than those in the West, and their calendars (of which there were many) were quite inaccurate, becoming useless after a few decades. The author says the goal was not understanding, but achieving tianren ganying (天人感应), which means resonance between heaven and man.

Thus, a calendar was essential for planting crops, while a comet, eclipse, or sunspot might be a bad omen, so if the Emperor was weak, reporting its existence would be bad luck for the Dynasty—possibly even indicating that he was losing the Mandate of Heaven (tianming 天命, which means destiny or fate). If he was powerful, reporting bad news would be bad luck (i.e. execution) for the astronomer, and the sunspot or comet went unrecorded.

The ancient Chinese cataloged more stars than Westerners, in some cases recording their positions with remarkable accuracy. But as in the West, they were limited to Magnitude +5 or so, which is the faintest that can be observed without a telescope, a Western invention that made modern astronomy possible.

This book spends a fair amount of space giving us a light overview of the Chinese dynasties, Chinese philosophy (Daoism, Confucianism, Legalism) and details of Chinese mathematics. Their math, like their astronomy, was purely practical, focusing exclusively on elementary computation. Though they discovered the Pythagorean relationship, they never invented the zero and their math never approached the level of abstraction or sophistication achieved by ancient Greece.

Thus, when the Jesuits brought the New Science to China, Chinese astronomy progressed rapidly. Matteo Ricci and Michele Ruggieri studied the language and adopted native customs, which made Xu Guangqi and others scholars more receptive to outside knowledge than they would normally have been. However, there were still misunderstandings. In one incident, a Chinese astrologer named Yang Guangxian accused the Jesuits of selecting an inauspicious date for a funeral. This and other incidents led to many execu­tions of Jesuits and the outlawing of Christianity in China in 1724.

The close connection between the government and astronomy meant that by the time of the Qing dynasty (1664–1912), education had declined to the extent that many Chinese mathematicians could not understand their own math.

Though the author uses the clumsy CE / BCE notation, he also uses a minus sign instead to represent BC dates, as in the sentence “In China, sunspot observa­tions date back to −28 and were documented by Liu Xiang 刘向 (−79 −8), an astronomer and alchemist.” This is a much better system.

apr 21, 2026

Terahertz Astronomy

by Christopher K Walker
CRC Press, 2019, 335 pages
reviewed by T. Nelson

If you’re looking for a nice, clearly written book on radioastronomy or an introduction to terahertz waves, this is the book you need.

Terahertz light (300 GHz–10 THz) falls into the technically challenging region between microwaves and far-infrared. The wavelength is too short for ordinary electronic components and too long for optical components. Much of the THz light is absorbed by the atmosphere. What gets through is contaminated by noise power caused by atmospheric water vapor. So new kinds of detectors and high-elevation observatories (or balloons) are needed to detect a signal.

What is there to observe at THz wavelengths? Hydrogen gas doesn’t have any transitions at THz wavelengths. This means what we would observe is carbon monoxide (CO, multiple transitions around 0.69–1.5 THz); carbon (C⁺, 1.9 THz); dioxygen (O₂, 4.7 THz); and water (especially at 557 GHz) in the interstellar medium (ISM). These line transitions are superimposed on a continuum of thermal emission from dust. The big advantage of THz is that the wavelengths are bigger than the interstellar dust particles, so there is little extinction compared to UV or IR.

Probably the most important emission line is C⁺ (CII), which is ubiquitous in the ISM. It is incredibly bright. The author says the Milky Way radiates ∼70 million solar luminosities just in this one line. It’s narrow enough that its Doppler shift is easy to measure. Physically, C⁺ is a marker of cooling in the vast interstellar space.

The book has a clear, easy-to-understand discussion of radiative transfer—an incredibly important topic in atmospheric studies—followed by a discussion of detector optics, bolometer arrays, observation techniques, and coherent detection systems. Some of the components, like SIS (superconductor-insulator-superconductor) mixers, give us the sensitivity needed for resolving THz transitions, but so far the imaging capability and number of pixels lag behind that of visible optics.

Each chapter includes color images, formulas, and a set of elementary problems. There’s no heavy math, so this book is great for reading while you’re waiting in a doctor’s office.

apr 22, 2026