directly on Mercury’s equator.

Mercury’s proximity to the Sun has historically caused astronomers difficulty. Even Copernicus, developing his theory that the planets revolved around the sun, was unable to see Mercury well enough to predict its orbit as accurately as he would have liked. Johannes Kepler determined the laws of planetary motion by using data collected earlier by his colleague Tycho Brahe. Later astronomers and mathematicians continued to struggle with Mercury’s unusual orbiting behavior and speed, even proposing that another planet (dubbed Vulcan) caused these anomalies. The concept of Vulcan was dropped when Albert Einstein resolved the problem mathematically in 1915 by proving that the sun’s extreme gravitational pull was the cause. Satellite Mariner 10 collected photos of Mercury’s battered surface in the 1970’s, and the planet’s unique properties will be closely scrutinized once more by the space probe MESSENGER, scheduled to approach Mercury in 2008. (MESSENGER is an acronym for MErcury Surface, Space Environment, GEochemistry, and Ranging.)

Sobel’s chapter on Venus, titled “Beauty,” offers a roundup of ancient legends and examines a number of reverent poems written by earthbound admirers. There is no doubt that the planet’s prominence in mythology and planetary lore is the result of its frequent, shimmering dominance of the night sky. Its appearance as the “evening star” or “morning star” (a designation it shares on occasion with several other planets) has resulted in generations of endearments. Thanks to his improvements to the telescope, Galileo was able to chart the phases of Venus. Future poets may be more constrained in their portraits of the planet, as it is now known that its surface is washed with sulfuric acid rain.

“Geography,” as Sobel calls the section on Earth, delivers a sweeping summary of the exploration of the planet after presenting an overview of Ptolemy’s use of astronomy in mapping it. In “Lunacy,” a segment on the moon, she replaces the beloved and legendary champion of romance with a portrait of a dry, dark, and dusty satellite whose reflected light is never quite bright enough to engender color within the range of human vision. Also, thanks to intense studies of the red planet, the “sci-fi” vision of Mars has given way to a harsher, if no less exotic, view: It is now known that its iron-oxide surface poses a deadly threat to life and that its solidified iron core is incapable of generating a magnetic field.

The gas planets of Jupiter, Saturn, Uranus, and Neptune stretch outward in space from the terrestrial planets. In the chapter “Astrology,” on Jupiter, the facts, as opposed to planetary lore, prove astonishing. Jupiter’s volume is one thousand times that of the earth, and it retains a cloudy cover made up of countervailing winds and jet streams, visible as dark belts and bright swaths, features that are constantly metamorphosing in centuries-long storms. Its colorful clouds obscure the dense inner sea of liquid hydrogen, so compacted in the depths of the planet that its liquid turns into an electrically charged metallic substance that actually composes the bulk of the planet.

Turning to “Music of the Spheres,” Sobel frames her discussion of Saturn musically, beginning with the English composer Gustav Holst’s 1916 orchestral suite The Planets. In this work, Saturn is characterized as the “Bringer of Old Age,” a role that Holst claimed entailed not only the decline of physical well-being but also a sense of fulfillment. In fact, as Sobel explains, the rings of Saturn incorporate distinct harmonic resonances.

Sobel cites the beauty of the Saturnian ring system as capable of attracting viewers to a lifetime interest in astronomy. Saturn’s resplendent rings (composed of dust and ice crystals) vary in visibility with the planet’s changing position in orbit, being fully displayed to viewers on Earth only every fifteen years. Following Galileo’s unfulfilled study of the rings, Dutch mathematician and astronomer Christiaan Huygens was able to prepare a diagram in 1659 revealing how the planet’s 29.5-year elliptical orbit actually progressed. The rings of Saturn resonate in relationships that accord with the rules of pitch developed by ancient Greek mathematician and astronomer Pythagoras. The resonance effect of the rings separates them, leaving empty spaces between, as proven when the Cassini spacecraft flew between the two rings known as F and G upon reaching Saturn in 2004.

Pluto, which Sobel dubs “UFO,” is now considered by some to be too small to fit planetary criteria, but it remains dominant in its region. Gerard Kuiper first predicted the existence of Pluto’s companions, icy exiles rejected from the inner solar system during its formative period and orbiting in what is known as the Kuiper Belt in honor of its discoverer. Scientists hope to learn more about the early formation of the universe from these planetoids.

Sobel explicates exciting new discoveries about the planets handily in her more straightforward scientific passages, and the celestial residents shine in splendor in her more poetic descriptions. However, her creativity sometimes results in overly cute and potentially misleading features. A Martian meteorite, fallen to Earth near the South Pole during the last ice age, narrates “Sci-Fi.” “Night Air” consists chiefly of a fictional letter from astronomer Maria Mitchell to fellow astronomer Caroline Herschel. Sobel’s previous work as translator of the 2001 volume Letters to Father: Suor Maria Celeste to Galileo, 1623-1633 may lead readers to assume that Mitchell’s letter is likewise authentic; only the “Details” section of seemingly random notes at the end of the book informs them otherwise. In “Astrology,” Sobel’s discussion of Galileo’s horoscope, as well as the inclusion of a natal chart for the space probe Galileo, may lead the unwary to infer that astrology is on a par with astronomy. More sophisticated readers may weary of Sobel’s tendency to anthropomorphize planets, meteorites, and even space probes.

Other readers, perhaps newly enchanted with the solar system thanks to Sobel’s succinct summary of astronomical data, may find such distinctions inconsequential. For many, Sobel’s brief tour of the solar system will provide a wealth of unexpected information concerning the planets’ motion, composition, and moons. Her descriptions of astronomical discoveries and breakthroughs will entertain readers unfamiliar with astronomical history. For better and occasionally for worse, Sobel’s mixture of science, myth, folklore, history, biography, science fiction, music, and astrology exercises its appeal at many levels.