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(minor planets; planetoids) Small rocky Solar-System bodies without atmospheres that orbit the Sun but are too small to be considered planets. The distinction between an asteroid, a comet, and a Kuiper belt object is rather blurred: the prevailing view is that most of these minor bodies are remnants of the protoplanetary nebula that failed to become incorporated into the planets during the accretion phase of the Solar System's formation. However, some astronomers have theorized that asteroids resulted from destructive collisions between a handful of Mars-sized bodies in the Solar System's remote past. These bodies would have been prevented from accreting into a planet by Jupiter's gravitational influence. Comets and Kuiper belt objects consist of a mixture of rock, dust, and ice, but asteroids, like meteoroids, are composed of rock and metal.

Most known asteroids (perhaps 95%) orbit in the asteroid belt, or main belt, between the orbits of Mars and Jupiter, at distances of 1.7 to 4.0 astronomical units from the Sun. These main-belt asteroids have periods between 3 and 6 years. The distribution of orbits within the belt is modified by Kirkwood gaps, regions that have been swept clear of interplanetary bodies as a result of orbital resonance with Jupiter. Some asteroids have orbits that are very different from those in the main belt; these include the near-Earth asteroids (i.e. the Amor, Apollo, and Aten groups), and members of the Trojan and Hilda groups. These bodies are thought to be either fragments that have broken away from large main-belt asteroids or else comets that are no longer active. The objects (2060) Chiron and Pholus, whose orbits lie out beyond Saturn, are sometimes considered to be asteroids but are technically classified as centaurs. There are also clusters or families of asteroids with very similar orbital characteristics (see Hirayama families). Like the planets, most asteroids follow direct orbits close to the plane of the ecliptic, although the average orbit has a larger eccentricity (0.15) and a greater inclination (9.7°) than those of most planets. A few objects, however, such as (944) Hidalgo, follow highly eccentric and inclined orbits more akin to those of some periodic comets. Their orbits taking them across the paths of the planets, and some make very close approaches.

Asteroids shine by reflected sunlight but only one, (4) Vesta, is bright enough to be seen with the naked eye. Astronomers believe that there may be several million asteroids in the Solar System, with about 60 000 new ones being discovered every year. Improved observational and photographic instruments and techniques account for this high discovery rate, but as of November 2005, only about 300 000 known asteroids had calculated orbits, and of these, only 120 000 had received permanent numbers. Many more, with less well-determined orbits, have been assigned temporary designations. Many numbered asteroids have also received names, usually bestowed on them by their discoverers, but today subject to strict guidelines issued by the Internal Astronomical Union's Small Bodies Names Committee.

Until the late 20th century, the diameters of even the largest asteroids could only be roughly estimated. Since 1970, however. studies of the polarization of reflected sunlight and of the brightness at visible and infrared wavelengths for a large number of asteroids has led to improved values for their albedos; the diameters have been recalculated from these values and from analysis of the occultation of stars by asteroids. Asteroids vary in size from the largest and first to be discovered – the 933-km-diameter (1) Ceres – to objects smaller than 1 km. There probably exists a continuous distribution down to the size of meteoroids – boulder-size and smaller; but it has been suggested that bodies should be 50 m or more in diameter in order to qualify as asteroids. Most asteroids are thought to be irregular in shape, causing them to vary in brightness as they rotate every few hours. Smaller objects predominate. There are only about 30 asteroids with diameters greater than 200 km.

The total mass of the asteroids is estimated at 2.3 × 1021 kg (about 3% of the Moon's mass). Ceres accounts for more than one-third of this mass.

The composition of asteroids varies somewhat as a function of distance from the Sun. Studies of asteroid spectra and polarizations show that the surface rocks are diverse and are similar to those of meteorites. It is now believed therefore that most meteorites are fragments of asteroids. The majority of asteroids resemble carbonaceous chondrite meteorites, whereas others appear to have a metallic or silicaceous surface; the latter are more common near the outer edge of the asteroid belt (see also C-type asteroids; S-type asteroids; M-type asteroids). This is an important clue to the composition of the pre-solar nebula from which the proto-asteroids condensed.

Before the 1990s, our information about asteroids depended entirely on Earth-based observations. Then in 1991, NASA's Galileo spacecraft, en route for Jupiter, encountered (951) Gaspra and took the first high-resolution photographs of an asteroid. Two years later, Galileo encountered (243) Ida and Ida's satellite Dactyl. Further asteroid encounters have followed, including the Near-Earth Asteroid Rendezvous (NEAR-Shoemaker) mission's visits to (253) Mathilde in 1997 and (433) Eros in 1999. NEAR-Shoemaker became the first human-made spacecraft to land on an asteroid when it touched down on Eros on Feb. 12, 2001, after orbiting it for a year.

See also Table 3, backmatter.


(religion, spiritualism, and occult)

An asteroid (meaning starlike or small star) is one of thousands of small planets, 95 percent of whose orbits lie between the orbits of Mars and Jupiter. Some have irregular orbits that carry them inside the orbit of Mars (the Apollo and Amor groups); some, even inside the orbit of Mercury (Icarus), Earth and Venus (Bacchus and Apollo). Others travel in the same orbital path as Jupiter (the Trojan asteroids). Initially, these planetoids were given mythological names, but as telescopes increased in strength and more and more asteroids were discovered, astronomers began naming them after places (e.g., Pretoria, Toronto, and Arizona) and people (e.g., Jonathan Murray, Rockwell Kent, and Christy Carol). Some of the smaller and more recently located asteroids have been given entertaining-sounding names, such as Bilkis (the Koranic name for the Queen of Sheba), Dudu (the dancing girl in Nietzsche’s Thus Spake Zarathustra), and Mr. Spock (named after the discoverer’s cat).

While most asteroids are no more than a few miles across, many are much larger. Ceres, the largest asteroid, is 620 miles in diameter. The main group of asteroids is located where Bode’s law would lead one to anticipate a planet, and one theory speculates that the asteroid belt is the debris of a former planet that has disintegrated into many pieces. Another theory speculates that at some distant time in the past when the solar system was being formed, the material circulating between Mars and Jupiter failed to coalesce into a cohesive planet, perhaps because of the disruptive influence of Jupiter’s tremendous gravity.

Except for a very few whose orbital paths carry them near Earth, asteroids are invisible to the naked eye. The asteroid belt was not discovered until the nineteenth century, so asteroids were not taken into account in traditional astrology. Even after sufficient information was available to construct ephemerides (tables of positions) of the major asteroids, astrologers chose to ignore them. Alan Leo tried to interest his fellow astrologers in asteroids but was unsuccessful. Perhaps the ongoing disputes over the astrological influences of the newly discovered planets discouraged astrologers from studying the significance of these relatively tiny bodies. The sheer number of asteroids would also discourage such exploration. Whatever the explanation, the astrological study of asteroids did not begin until the last quarter of the twentieth century.

The real founder of asteroid studies was Eleanor Bach, who in the early 1970s published an ephemeris and a set of interpretations for the first four asteroids (sometimes called the Big Four) to be discovered—Ceres, Pallas, Juno, and Vesta. Zipporah Dobyns followed in 1977 with a similar work on the Big Four. Emma Belle Donath also published a set of books dealing with the four major asteroids. In 1986, Demetra George and Douglas Bloch’s Asteroid Goddesses was published. Building on the work of its predecessors, this book quickly became the definitive study of Ceres, Pallas, Juno, and Vesta. It contained everything needed to locate and interpret the four major asteroids in a natal chart. George, the primary author, also integrated the feminist theory of the primordial goddess religion (the notion that all of our more distant ancestors were goddess worshipers) into her discussion, giving Asteroid Goddesses tremendous appeal in a subculture where the idea of a primordial goddess religion was widely accepted. The book enjoyed such success that a new, expanded edition was published four years later. The general availability of Asteroid Goddesses, the basic appeal of the goddess notion, and the integration of asteroid positions into most computer chart-casting software programs all combined to make Ceres, Pallas, Juno, and Vesta easy to use. Thus, the general acceptance and continually expanding use of the four major asteroids by the larger astrological community was ensured.

The focus on Ceres, Pallas, Juno, and Vesta by asteroid advocates has generally eased the anxiety of astrologers who resisted the introduction of hundreds of new points demanding interpretation in a horoscope. Yet, the widespread acceptance of the Big Four only made the question of the significance of the other asteroids more insistent. Those who have studied the astrological influence of asteroids have reached a consensus, which is, to quote from J. Lee Lehman’s The Ultimate Asteroid Book: “1. The asteroids have astrological effects which may be studied. 2. The name of an asteroid has astrological significance.”

The most common way of studying the influence of a new astrological factor is to study people in whose charts the factor is prominent, such as when an asteroid is in very close conjunction with a key planet or with the ascendant. The essential clue is the name of the asteroid, which gives preliminary insight into the asteroid’s astrological “temperament,” because the names astronomers give to newly discovered celestial bodies are not coincidental—by virtue of some nonapparent synchronistic influence, nonastrologically inclined astronomers give them astrologically significant names. For example, with regard to the asteroid Eros, an astrologer would anticipate that it was somehow related to passion, yet its name was assigned by an astronomer for whom asteroids were little more than big space rocks.

In The Ultimate Asteroid Book (1988), Lehman attempted to overcome some astrologers’ resistance to asteroid use by asserting that asteroids have few concepts allocated to them and that their being small and numerous may allow for many very exact meanings. For example, Eros specifically means “passionate attachment,” and so does not have a broad range of meanings. (One can only wonder about the concepts associated with asteroids such as Dudu.) Lehman contrasts this specificity with the multivalent significance of a planet like Venus, which can refer to “love, harmony, magnetic attraction, the veins, diabetes, erotica, potatoes, or a host of other things.”

Beginning with a preliminary clue, such as, in the case of Eros, the idea that this small celestial body is somehow related to passion, the astrologer would place Eros in the charts of acquaintances as well as in those of famous people whose lives are open to public scrutiny. One would anticipate that natives with Eros in conjunction (or in some other close aspect) with the Sun, the ascendant, Venus, or Mars might exhibit more “erotic” inclinations than people with a less prominent Eros. One could not, however, know the specific nature of these inclinations—and how they differed from the passions of Venus, Mars, and Pluto—until after studying many people with Eros prominent in their chart. This approach to the study of new astrological factors is the same methodology utilized by astrologers to uncover the nature of the “new” planets Uranus, Neptune, and Pluto.

There were several reasons for the initial focus on the Big Four. Ceres, Pallas, Juno, and Vesta were the first asteroids to be discovered—in 1801, 1802, 1804, and 1807, respectively—and there was a 38-year gap before other asteroids were located. Thus, they belong together in a fairly natural grouping. Beyond the Big Four, however, asteroid research has not proceeded in a systematic manner. Rather than studying either the next asteroids to be discovered, or the next-largest asteroids, researchers have jumped to the study of asteroids with intriguing names such as Eros and Amor, or asteroids with eccentric orbits, such as Adonis and Icarus. These are all relatively tiny bodies: Eros is 18 miles across at its widest, Amor is approximately 2 miles in diameter, and Adonis and Icarus are both about 1 mile wide. By comparison, Hygiea (personification of health or hygiene), Psyche (personification of the soul), Kalliope (muse of epic poetry), and Laetitia (Latin for “gladness”) are all larger than Juno (150 miles in diameter), but almost no information is available on any of these bodies except Psyche. (Short summary meanings of these asteroids are given in Martha Lang-Wescott’s Mechanics of the Future: Asteroids.)

By sequence of discovery, the next four asteroids after the Big Four are Astraea, goddess of justice; Hebe, goddess of youth who took ambrosia to the gods; Iris, goddess of the rainbow who was a messenger between the gods and humanity; and Flora, goddess of flowering plants. Again, little information on any of these four asteroids is available except for short summaries in Lang-Wescott’s survey. The clues that one would use to research any one of these “concept” or “goddess” asteroids—health, justice, poetry, gladness, and so forth—are all appealing, so the lack of attention they have attracted is surprising. Clearly, the next step in establishing the study of asteroids as a widely accepted branch of astrology will be the systematic exploration of the larger or the earlier asteroids, rather than the current piecemeal study of asteroids with idiosyncratic appeal.

One issue that emerged when astrological asteroid studies was beginning to attract serious interest was the question of sign rulership. It was traditionally held that the Sun and the Moon (the two luminaries) ruled one sign apiece, Leo and Cancer, respectively. The known planets each ruled two signs: Mercury ruled Virgo and Gemini; Venus ruled Taurus and Libra; Mars ruled Aries and Scorpio; Jupiter ruled Sagittarius and Pisces; and Saturn ruled Capricorn and Aquarius. When the “new” planets were discovered, astrologers determined that Uranus ruled Aquarius, Neptune ruled Pisces, and Pluto ruled Scorpio, leaving Saturn, Jupiter, and Mars as the rulers, respectively, of Capricorn, Sagittarius, and Aries. In this modified system, only Mercury and Venus still rule two signs each. The attractiveness of a balanced system in which 12 heavenly bodies rule 12 signs has often led twentieth-century astrologers to speculate that two new planets would eventually be discovered and come to be accepted as the rulers of Virgo and Libra.

Some asteroid-oriented astrologers speculated that the larger asteroids ruled these signs. Bach, the founder of astrological asteroid studies, assigned Ceres and Vesta the rulership of Virgo, and Juno and Pallas the rulership of Libra. Zipporah Dobyns, another pioneer in the field of asteroid research, accepted the Big Four as corulers (with Mercury and Venus) of these two signs. However, spreading out sign rulerships to more than one planet did not strike a favorable chord among nonasteroid astrologers. Not only did multiple rulership lack elegance, but it also made certain astrological procedures, such as identifying the significator in horary astrology, somewhat schizophrenic. Beyond the question of elegance, some of the sign associations were strained. Ceres, which embodies the quality of nurture, for example, is clearly more related to Cancer than to Virgo. Another question one might ask with respect to asteroid rulerships is: Why stop with the Big Four? The asteroid Hygiea, the personification of health and hygiene, is clearly related to Virgo; the asteroid Astraea, the goddess of justice, has definite affinities to Libra; and so forth. The point is, while various asteroids may be associated with the 12 signs of the zodiac, assigning rulerships to asteroids raised more problems than it resolved.

In more recent years, the exploration of the astrological significance of asteroids has been overshadowed, if not derailed, by two developments: the emergence of Jyotish (Vedic astrology) and classical Western astrology as major topics of astrological interest, and the complexification of asteroid studies as the result of the discovery of numerous new objects, including hundreds of large planetoids beyond the orbit of Neptune.

As a result of translation and interpretive activities that matured in the last decades of the twentieth century, both Jyotish and classical astrology emerged as major sources of sophisticated astrological techniques that are simultaneously new (from the perspective of astrologers who matured under the influence of modern psychologically oriented astrology) and time tested. Both of these two traditions are not only rich in astrological insights, but they also completely ignore the modern planets—Uranus, Neptune, and Pluto—as well as the new planetary bodies. Thus, not only have Jyotish and classical astrology diverted interest away from new areas of astrological research, such as asteroid studies, but many of the astrologers who have become involved in this renaissance seem to have acquired an active prejudice against considering anything that was not originally a part of these traditions.

As a result of the exploration of our solar system, particularly since the advent of the Hubble space telescope, astronomers have discovered numerous new asteroids, including a host of large bodies orbiting the Sun beyond Neptune. Some of these Plutolike bodies, referred to as plutinos, are almost as large as Charon, Pluto’s moon, and in at least the case of Ixion, significantly larger than Charon. Beyond adding numerous new planetoids—which further complicates the field of astrology—these newly discovered bodies have even caused astronomers to consider dropping Pluto from the planet category. This hypothetical reclassification of Pluto would, in turn, call into question modern astrology’s use of Pluto and of the other nontraditional planets and planetoids, thus dovetailing with the negative perspective of many traditional astrologers.

Despite this situation, it nevertheless seems almost certain that asteroid studies have a future as a significant field of astrological research. If nothing else, the four major asteroids have become too well established in the mainstream of contemporary astrological practice to ever be dropped. Additionally, the incorporation of asteroids beyond the Big Four into multiple astrological software programs means that the necessary tools are within easy reach of any aspiring astrological researcher. These factors and others provide a solid foundation from which asteroid studies is likely to reemerge as a major field of interest, particularly after the current fascination with traditional astrology peaks.

All major Western astrology software programs allow one to incorporate Ceres, Pallas, Vesta, and Juno into natal charts, progressed charts, etc, and in every way to treat them on par with the planets. Astrolabe and Matrix also market separate report programs for the four major asteroids. Add-on software programs for the other asteroids can be obtained for the Solar Fire calculation program from Esoteric Technologies and for the Kepler calculation program from Cosmic Patterns Software. At this writing, the current (fifth) edition of Kepler allows one to calculate the position of 1000 asteroids for any chart. An add-on program for more than 20,000 asteroids is also available. The asteroid add-on for Solar Fire allows one to calculate the positions of 10,000 asteroids. Additionally, Solar Fire can place any of these asteroids in an extra chart ring—something one cannot do in current editions of most other programs. Mark Pottenger’s freestanding asteroid DOS program can also be used to place a certain number of asteroids in the chart of his CCRS horoscope program—both available through Astrolabe. Finally, one can find the astrological positions of asteroids in a natal chart from online sites such as Astro Deinst at


Brau, Jean-Louis, Helen Weaver, and Allan Edmands. Larousse Encyclopedia of Astrology. New York: New American Library, 1980.
Dobyns, Zipporah. Expanding Astrology’s Universe. San Diego: ACS Publications, 1983.
Donath, Emma Belle. Asteroids in Midpoints. 1982. Tempe, AZ: AFA, 1982.
Donath, Emma Belle. Asteroids in the Birth Chart. 1979. Reprint, Tempe, AZ: AFA, 1991.
George, Demetra, with Douglas Bloch. Asteroid Goddesses: The Mythology, Psychology and Astrology of the Reemerging Feminine. 2nd ed. San Diego: ACS Publications, 1990.
Lang-Wescott, Martha. Mechanics of the Future: Asteroids. Rev. ed. Conway, MA: Treehouse Mountain, 1991.
Lehman, J. Lee. The Ultimate Asteroid Book. West Chester, PA: Whitford Press, 1988.
Press, Nona. New Insights into Astrology. San Diego: ACS Publications, 1993.
Schwartz, Jacob. Asteroid Name Encyclopedia. St. Paul, MN: Llewellyn Publications, 1995.
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