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Space Digest                Mon,  7 Jun 93       Volume 16 : Issue 693

Today's Topics:
      Electronic Journal of the ASA (EJASA) - June 1993 [Part 1]

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Date: Sun, 6 Jun 1993 19:09:46 GMT
From: Larry Klaes <[e-mail]>
Subject: Electronic Journal of the ASA (EJASA) - June 1993 [Part 1]
Newsgroups: sci.astro,sci.space,sci.misc,sci.classics,sci.archaeology,alt.sci.planetary

                           THE ELECTRONIC JOURNAL OF
                   THE ASTRONOMICAL SOCIETY OF THE ATLANTIC

                       Volume 4, Number 11 - June 1993

                         ###########################

                              TABLE OF CONTENTS

                         ###########################

          * ASA Membership and Article Submission Information

          * Marcus Manilius and Ancient Astronomy - Ian Bacon

          * Perseids 1993: Shower or Storm? - Peter Brown

          * Cometary Conundrums - M. Leon Knott

                         ###########################

                         ASA MEMBERSHIP INFORMATION

        The Electronic Journal of the Astronomical Society of the Atlantic
    (EJASA) is published monthly by the Astronomical Society of the
    Atlantic, Incorporated.  The ASA is a non-profit organization dedicated
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        ASA membership application is open to all with an interest in
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        Council - Bill Bagnuolo, Michele Bagnuolo, Don Barry, Bill Black,
                  Mike Burkhead, Jeff Elledge, Frank Guyton, Larry Klaes,
                  Ken Poshedly, Jim Rouse, Tano Scigliano, John Stauter,
                  Wess Stuckey, Harry Taylor, Gary Thompson, Cindy Weaver,
                  Bob Vickers


                             ARTICLE SUBMISSIONS

        Article submissions to the EJASA on astronomy and space exploration
    are most welcome.  Please send your on-line articles in ASCII format to
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        or - [e-mail]
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                                DISCLAIMER

        Submissions are welcome for consideration.  Articles submitted,
    unless otherwise stated, become the property of the Astronomical
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    by the Astronomical Society of the Atlantic, Incorporated.


                      MARCUS MANILIUS AND ANCIENT ASTRONOMY

             by Ian Bacon with the assistance of Dr. Jane Bellemore

            Courtesy of Paul Dickson ([e-mail]),
          Editor of the Saguaro Astronomy Club's newsletter, SACNews,
          in Phoenix, Arizona.

        Marcus Manilius, a Roman poet of the early Imperial period, is one
    of the least known astronomers of the ancient world.  His work, "The
    Astronomica", is largely derivative, conveying little new information
    on ancient astronomy.  Not withstanding this, Manilius does present
    areas of interest for scholarship.  In this paper will look at his
    life and work in some detail.  In order to do that we shall first
    place Manilius and ancient astronomy into their cultural backgrounds.

        All ancient civilizations - the Chinese, Babylonians, the Greeks,
    and the Romans - had some interest in the sky.  This interest ranged
    from the mundane tasks of maintaining the calendar and assisting
    navigation to that of astrological predictions.  However, it was
    the Greeks who first applied deductive logic to the examination of
    the material Universe and distinguished astronomy from astrology.
    Beginning in the Fifth Century B.C. and continuing to the First
    Century B.C., the Greeks founded and made large-scale progress in
    the science of astronomy.

        This progress included knowledge of the sphericity of the planet
    Earth, the existence of the Zodiac/ecliptic, the movement of the
    planets, explanation of and limited prediction of solar and lunar
    eclipses, not inaccurate measurements of the relative sizes of Earth,
    the Sun, and the Moon, the creation of a stellar positional system
    based on the ecliptic (an ecliptic coordinate system with celestial
    latitude and longitude) with a one to six stellar magnitude system
    (still with us today), and of course, a calendar.

        The Greeks established the basics of astronomy.  However, they and
    subsequently the Romans were hampered by their conceptualization of
    the Universe, that of a "perfect" heaven with perfect circles.  This,
    with an Earth-centered, geocentric Universe, resulted in increasingly
    complex models to explain planetary behavior.  Each planet (and the
    Sun) was made to move around Earth in a perfect circle.  To explain
    discrepancies between theory and observation, circles were added to
    circles in an ascending order of complexity.  Increasingly complex
    constructs of epicycles, eccentrics, and equants formed which
    persisted unchallenged through the European Middle Ages, the Arab
    world, and into the Sixteenth Century European Renaissance.

        Greek and Roman science was not only restricted conceptually
    but also restricted by a low level of technology.  There were few
    instruments and their accuracy was poor.  Ancient mathematical systems
    were limiting.  There were two mathematical systems used by Greek
    astronomers, one of which did not have a place value, nor did it
    recognize the importance of zero, nor could it manipulate fractions
    well.

        The other system, inherited from Mesopotamia and the Babylonians,
    was a place value system with a zero but a base sixty mathematical
    system (the basis for our 360 degrees, with sixty minutes and seconds
    of arc and time).  Added to this, there were no aids to calculation;
    even the humble logarithm was not developed till the Sixteenth
    Century.  These factors placed a limit on scientific progress.

        This is typified by one of Greece's greatest astronomers, Hipparchus.
    Living in the Second Century B.C., Hipparchus was essentially the last
    of the original thinkers of Greek science.  Only one of his minor,
    earlier works directly survives, but his research is much discussed
    and used by his successors.

        Hipparchus is known to have constructed the first model of lunar
    and solar motion based on observational evidence, discovered the
    precession of the equinoxes, possibly the first to use trigonometry in
    his calculations, and determined the length of the tropical year to
    365.25 days with an error of plus or minus five minutes.  Hipparchus
    had a passion for observational accuracy and the use of mathematics to
    solve problems.  This is demonstrated by his refusal to construct a
    solar system theory, as he believed there was insufficient data and
    mathematical tools to do so accurately.

        However, within their limits, the Greeks made greater scientific
    progress than any of their cultural predecessors.  The Greeks invented
    the concept of deductive and inductive logic, and rational thought,
    one half of the scientific method paradigm of theory and empirical
    research.  From this flowed progress in all fields of human endeavor:
    Science, medicine, mathematics, architecture, and more.  As with
    astronomy, much of this was not equaled until the Sixteenth and
    Seventeenth Centuries.

        By the First Century B.C., the Roman world of Italy and western
    Europe had fallen under the spell of Greek and Near Eastern cultural
    influences:  Upper-class Romans spoke and read Greek, their children
    studied in Athens, Greek words entered the Latin language, and Greek
    art and philosophy were necessities in any house of distinction.  One
    of these new Eastern influences entering Rome were the joint beliefs
    and knowledge of astrology and astronomy.

        Astronomy was by and large not important to the Romans beyond
    its ulitarian functions.  Even then the Roman calendar was an active
    example of political neglect until Julius Caesar, returning from Egypt
    and Cleopatra, corrected it.  In the field of astronomical observation
    and theory, the Romans did little, relying on earlier Greek theories
    and observations as the basis for any speculation.

        Astrology played an ambivalent role in the Roman world.  It was
    practiced by many prominent Romans, including the Emperor Tiberius
    (14-37 A.D.).  The Second Century A.D. Roman historian Suetonius,
    writing in THE TWELVE CAESARS, tells us that the future Roman Emperor
    Augustus, as a young man, visited an astrologer to uncover his fate:
    The stars foretold his greatness.

        Suetonius continues with a similar anecdote in which another
    astrologer, the Roman Publius Nigidius Figulus, also made the same
    prediction concerning Augustus.  Despite some public acceptance,
    astrology was harshly dealt with by the Roman authorities when its
    usage caused public disorder or threatened political security.  At
    various intervals, usually related to political upheaval, astrologers
    were expelled from Rome.

        There are nine recorded expulsions of astrologers between 139
    B.C. and 93 A.D..  The supposed cause of these expulsions was public
    disorder caused by their astrological predictions.  After the
    transformation of Rome from a Republic to an Empire, ruled by an
    Emperor, the rationale behind official action against astrology
    changed somewhat.  Political concern centered around the longevity
    of the Emperor and his potential successor.  In 11 A.D., the Emperor
    Augustus (in his seventy-fourth year, three years before his death)
    forbade the prediction of a person's death and published his own
    horoscope - both, presumably, to minimize speculation as to the time
    of his own passing.

        The aim of these expulsions, which also included that of
    philosophers, mystics, and diviners, was not to discredit or destroy
    astrology but to curtail the politically significant activities of its
    practitioners.  Part of the official concern was that astrology, and
    other means of divination, would be used to predict the Emperor's
    death.  This is not to suggest that the Roman culture gave astrology
    full faith and credence, but a prediction used at the appropriate
    moment could destabilize an Emperor's position or encourage a revolt.
    The mere claim that a prominent person had asked these question of an
    astrologer became grounds for treason.

        It is important to put ancient astrology into its cultural
    context.  The ancients were not technologically advanced.  While many
    today heap scorn on those who believe and practice astrology in the
    modern world, we should remember that those in the ancient world
    lived surrounded by forces of nature that they neither understood nor
    controlled.  We should not criticize the ancient astronomers for their
    belief and practice of astrology but remember that the great names of
    modern astronomy - Copernicus, Brahe, etc. - also practiced astrology
    to pay their bills.

        It is with this cultural background that we turn to the main topic
    of this paper, Marcus Manilius.

        All that we know of Manilius comes to us from his work, a poem
    explaining the "science" of astrology to his audience.  The poem is
    known as "The Astronomica".  It is divided into five "books",
    essentially chapters, totaling approximately twenty-five thousand
    words.  Books Two through Five discuss astrology in great detail.
    However, Book One forms an introduction to the later astrological text
    by providing an astronomically-oriented summary of the heavens.  This
    book tells us something of Manilius' perception and knowledge of the
    Universe.  Unfortunately, while he does describe much in detail, he
    gives no specific, datable events.

        What we have gleaned from Manilius' work is that he lived and
    wrote in the reigns of Augustus, the first Roman Emperor, and
    Tiberius, Augustus' successor.  Their combined reigns covered the
    period circa 30 B.C. to 37 A.D..  Manilius evidently had a good
    education and the leisure and income to spend years pursuing his goal.
    His motivation for writing "The Astronomica" is as hard to fathom.
    He may have felt he had a message to give to the Roman world.

        It is not known if Manilius wrote other works since none appear to
    have survived.  It is also unknown how successful his work was to his
    contemporaries.  Internal evidence suggests that Manilius' wrote
    between circa 10 to 20 A.D..  One translator of Manilius, G. P. Goold,
    gives us indications that contemporary authors may have used Manilius
    as a minor source.  There is no major reference to his work until the
    Fourth Century.  He was not considered one of the great authors of
    antiquity.

        After the Fifth Century A.D., Europe entered the early Middle
    Ages, where little or no science of any description was practiced.
    During this period, "The Astronomica" languished in monasteries.  In
    the Tenth Century, "The Astronomica" was mentioned twice, once by the
    Roman Catholic Pope Sylvester II and once in a catalogue of books.

        There are now about twenty copies in existence preserving three
    different versions of the original text, all with minor gaps.  These
    texts date from the Eleventh and Fifteenth Centuries, when they were
    themselves recopied from earlier works.  It has been the work of
    classicists in the Nineteenth and Twentieth Centuries to analyze
    and produce a reliable version of Manilius' original work.

        The time in which Manilius wrote was the culmination of a
    tumultuous period of Roman history:  The transformation of the
    Republic, a landed oligarchy (with democratic elements), into the
    autocratic Roman Empire, ruled by an Emperor.  This transformation was
    implemented at great cost in human life and suffering.  Manilius and
    his contemporaries looked back upon this period before the Empire as
    a period of social decay and anarchy.  They feared its return and
    considered Augustus and the Imperial system he created their protection
    against its return.  Manilius supported the Imperial regime created by
    Augustus.  His work is dedicated to Augustus and where possible takes
    the opportunity to praise the accomplishments of Rome's first Emperor.

        In addition to being an astrologer, Manilius was an adherent of
    Stoic philosophy.  Stoicism had been founded in Athens four centuries
    earlier.  It came to Rome during the Second Century B.C., finding
    acceptance amongst a portion of the Roman population.  Its credo of
    duty to the state and personal morality found appeal amongst a
    population undergoing cultural and political transformation.  The
    full social ramifications of Rome's conquest of the Mediterranean
    in the Second Century B.C. affected Roman society.

        Later, during the Imperial period, Stoics were, by and large,
    passively supported by the state.  One of Stoicism's tenets was
    acquiescence to authority - a worthy principle in an autocratic state.
    Other Stoic tenants perhaps held less appeal, since Greek Stoicism
    contained a theoretical belief in sexual equality and the abolishment
    of slavery.  Even the Greeks observed these more in the breach than
    the observance.  The Romans adapted Stoicism to their own more
    practical culture.

        Stoic philosophy provided a guide to all aspects of life and
    thought.  Within this design there was an astronomical belief system.
    Stoics believed in a "living", cyclic Universe that periodically
    destroyed and then reconstituted itself.  The "elements" of fire, air,
    water, and earth formed the basis of this Universe.  God, as a rather
    abstract concept, permeated and was part of the entire Universe.
    Earth was the center of the Universe with the Moon, Mercury, Venus,
    Sun, Mars, Jupiter, Saturn, and the stars (in that order from our
    planet) revolving in perfect, circular paths around Earth.  Due to
    the interrelationship between all components of the Stoic Universe,
    a change in one part was thought to cause a change in another.  This
    axiom gave astrology a rational basis:  A change in the heavens
    foretold a change on Earth.  Manilius wrote his astrological work
    from a Stoic perspective.

        In creating his work, it seems that Manilius was in part refuting
    a rival philosophy to Stoicism, that of Epicureanism.  Founded by the
    Greek philosopher Epicurus three centuries earlier, Epicureanism was
    a philosophy oriented less towards disciplined service to the state
    than towards a life of self-fulfillment and enjoyment.  In one letter,
    Epicurus wrote that "We say that pleasure is the beginning and end of
    living happily".  This found less acceptance in the Imperial period
    where unstinting (and unquestioning) service to the state was viewed
    with favor.  Writing approximately fifty years earlier than Manilius,
    the Roman poet Lucretius - himself an active practitioner of the
    Epicurean lifestyle - expounded this philosophy to the Roman audience
    in his work, "De Rerum Natura" (Concerning the Nature of Things).

        Two of the prime axioms of Epicureanism that reach us in the
    surviving work of Lucretius are that the Universe does not have a
    divine origin and that reason alone must be used to examine the
    Universe.  These, and an "atomic" theory (that all matter is composed
    of small, eternal, and indivisible particles), endeared this
    materialistic philosophy to scientists of the Seventeenth Century
    A.D. and onwards, while creating continual polemic with the Stoics
    of antiquity.

        There are a number of passages by Manilius which seem to refute
    precise passages written by Lucretius.  There are also similarities in
    the two works as to the layout of some arguments.  It is a reasonable
    assumption that Manilius identified arguments in Lucretius and set out
    to discredit them in his own work.  The slow pace of philosophical
    debate in the ancient world makes a fifty-year exchange of academic
    criticism possible.  By praising Augustus and criticizing Epicureanism,
    Manilius is playing his part in the maintenance of the Imperial order,
    and countering a rival philosophy.

        There are parallels between Manilius and another earlier author,
    Aratus of Soli, a Greek Stoic poet who wrote an astronomical poem, the
    "Phaenomena", circa 275 B.C..  His work gives astrology a minor role.
    What makes Aratus' work of particular interest is that it is allegedly
    based on the work of one of the greatest Greek astronomers, Eudoxus
    of Cnidos (circa 390 to circa 340 B.C.).  Regrettably, none of
    Eudoxus' works survive directly.  We rely on the reporting of others
    for information on his accomplishments.

        Aratus' work was popular in ancient Rome.  There are four extant
    translations of it from Greek into Latin.  As a noted Stoic author, it
    is not surprising that Manilius used Aratus as a template for his own
    work.  Proof that he assiduously followed the format of Aratus is his
    continuation of an erroneous point made by his Greek exemplar.  While
    describing the celestial poles, Manilius refers to them as "fixed and
    unchanging".  This is also the description given by Aratus.  In circa
    140 B.C., the Greek astronomer Hipparchus discovered the precession of
    the equinoxes, invalidating Aratus' earlier statement, but Manilius
    had not incorporated this discovery into his own work.

        What this lapse tells us is uncertain.  It must be remembered that
    Manilius was writing an astrological work of art, not an astronomical
    treatise.  It is not impossible that he simply disregarded the empirical
    materialist Hipparchus as irrelevant to the true aim of his work and
    followed the popular Stoic Aratus.  In a similar fashion, modern
    astrologers still use a geocentric Universe essentially unchanged
    from the time of Manilius as the basis for their predictions.

        It is reasonable in any case to conclude that Book One of Manilius'
    work, which is a astronomical introduction to the full work, is based
    on the work of Aratus.

        Manilius' work is aimed at a sophisticated audience.  It is not a
    practical "hands on" guide to casting a horoscope but the equivalent
    of an academic discussion of astrology.  In this it seems to follow
    the imperial aversion to predictive astrology.

        Manilius begins Book One by telling his readers about the
    background of astrology:  How men in "primitive" times did not
    know the "why" of the Universe but after careful research knowledge
    increased until the peak of learning was mastered - that of astrology.
    Manilius firmly identifies with astrology and regards astrology as
    the culmination of human scientific progress.

        Manilius next describes various cosmological theories, asking:
    Does the Universe have a beginning or end; was it born from chaos; is
    it composed of atoms or of the four elements (earth, water, air, and
    fire)?  His greatest effort is reserved for a detailed explanation of
    his own Stoic philosophy.  There is a curious parallel between these
    theories and modern cosmological thought.  However, rest assured,
    that any perceived similarity between Manilius' suggestion that the
    Universe has no beginning nor end and the Steady State Theory is
    purely coincidental.

        In Book One, Manilius is at pains to prove to the reader that
    Earth is a sphere.  He mentions Earth's shadow during lunar eclipses.
    He particularly notes the star Canopus, which was not visible from
    Rome but visible further south from Rhodes.  This continued emphasis
    on the spherical Earth suggests a hidden motive.  Lucretius wrote that
    a spherical Earth where people and animals walk about "upside down"
    was ridiculous.  In this case Manilius refutes Lucretius and
    Epicureanism.  It is also reasonable to assume that he was attempting
    to prove the fact of a spherical Earth to a skeptical lay audience.

        Next the constellations were described.  The constellations we
    possess today are those known by the Greeks and Romans.  However,
    the ancient constellations did not cover the entire sky.  Some stars
    were outside any constellation.  Such stars were "associated" with
    a neighboring constellation.  Manilius begins his description of
    the constellations with the Zodiac, continues with the northern
    constellations, and then concludes with the southern.  Manilius
    lists forty-six constellations, two of which are errors on his part.
    The furthest south of these is Centaurus.  At the end of his list
    of constellations, Manilius states that "they are the roof of the
    Universe".  The stars, in his opinion, formed the sphere most
    distant from Earth.  They were at the "top" of the sky.

        In Manilius' time there existed a sky slightly different from our
    own.  Two thousand years of precession lies between us.  For Manilius
    the first point of Aries was in Aries.  The north celestial pole lay
    near Beta Ursa Minor, twelve degrees from its present position near
    Polaris.  Polaris was just another second magnitude star.  From
    southern Egypt the Southern Cross was visible just above the horizon.
    Manilius relates how seafarers, particularly Phoenicians (the ancient
    inhabitants of what is now Lebanon), used both Ursa Minor and Major
    (the Little and Big Bears) for navigation, but preferred Ursa Minor
    as it was the more accurate, though fainter, guide.

        Manilius does refer to the theoretical existence of southern
    constellations.  This is partly given as additional proof of the
    sphericity of Earth.  He tells us that the southern sky will be filled
    with "ordinary" constellations and not strange or unusual figures.  It
    is Manilius' belief that the southern sky has constellations similar
    to the northern.  He suggests this for he believes the two halves of
    the heavens should "balance".  It may be that he is striving to
    suggest to his readers that the southern sky is essentially the same
    as the northern.  At this point in history no living Mediterranean
    dweller had reported seeing the far southern sky.  As always, the
    great unknown generated fantasies of mythical existences which
    Manilius tried to refute.

        Manilius' description of the constellations varies.  Some are
    merely listed ("...these the Crab follows, then the Lion, then the
    Virgin...") while others, usually the brighter and larger ones, are
    described in more detail ("...Orion may be seen stretching his arms
    over a vast expanse of sky and rising to the stars with no less huge
    a stride.  A single light marks Orion's head, which is impeded in
    high heaven with his countenance remote.  It is Orion who leads the
    constellations as they speed over the full circuit of heaven...").
    Many constellations have a description of their mythological
    background.

        It is clear from this form of description that Manilius was not
    attempting to write a quantitative catalogue of stellar positions.  If
    we look at the stellar catalogue of Ptolemy Claudius, written almost
    two centuries later, we see a list of stars containing celestial
    latitude, longitude, and a visual magnitude.  Manilius' work is very
    different.  As a philosophical and poetical artist writing at a
    conceptual level, Manilius may have regarded such formal enumeration
    of the sky as irrelevant to this work.

        A curious lack in Manilius is the limited discussion of the
    role of the planets.  The planets play a large role in astrological
    prediction, both in modern and ancient astrology.  Yet Manilius
    mentions them only in passing, in the context of discussing other
    celestial phenomena.  This gap in Manilius' work has been used to
    suggest that part of it is missing, that it was not completed, or
    that possibly Manilius attributed a lesser role to the planets.
    This question deserves further research.

        Manilius does give some information on the planets.  He states
    the relative distance of the planets:  Furthest from Earth is Saturn,
    followed by Jupiter, Mars, Venus, Mercury, and the Moon.  Planetary
    retrograde motion is described as strange and "backward moving stars
    (planets)".

        Manilius continues his narrative by describing the circles of the
    sky.  Into this category he places the Zodiac, the Celestial Equator,
    the Milky Way, the Tropics of Cancer and Capricorn, and the Arctic and
    Antarctic Circles.

        In his description of the Zodiac we receive a catalogue of the
    constellations and prominent stars.  The Zodiac is "from which the
    whole scheme of destiny is derived", a clear indication of its
    importance to an astrologer.  On several separate occasions, Manilius
    refers to the Zodiac as having "twice six" constellations.  This form
    of enumeration harks back to the Babylonians, demonstrating the
    ultimate source of Manilius' information.  In the later books,
    describing astrological calculations in detail, the zodiacal
    constellations receive a far more in-depth appraisal.

        Lastly, Manilius describes comets.  Comets were considered evil
    and bringers of misfortune in ancient and Medieval society.  The Roman
    author and Stoic Seneca, writing fifty years after Manilius during the
    reign of Emperor Nero, devotes a book/chapter of his "Natural History"
    to comets.  He reports how comets are associated with Earthly
    disaster.  Even English author William Shakespeare's tragedy "Julius
    Caesar" mentions the ill effects of comets.  Caesar's wife advises her
    husband, on the Ides of March (March 15), that comets foretell "the
    death of princes".  Caesar was murdered that day in 44 B.C..

        Manilius tells us of the various theories of the origin of comets:
    That of Aristotle where comets are inflammable Earth vapors ignited by
    dry air; of Diogenes Apolloniates, where comets are wandering stars;
    or the gods' means of warning humans of impending tragedy.  The last
    is also Manilius' belief.

        One very interesting point to be noted from book one of "The
    Astronomica" is a reference to the color of the star Sirius, the Dog
    Star.  A question as to the ancient color of Sirius is occasionally
    discussed by modern astronomers.

        Due to its brightness, Sirius received a degree of popular
    prominence in ancient society.  As its helical rising occurred in
    mid-July, it came to be associated with summer heat.  There are
    references to Sirius scorching fields, causing rabies (a "burning"
    disease), and being the bane of farmers.  In reality, the star was
    over eight light years from Earth.

        Evidently Sirius' helical rising was regularly observed, for its

    appearance allegedly foretold the health of the coming year.  Due to
    scintillation, Sirius' appearance at these times was that of a bright,
    flickering red star.  This visualization of a "red" Sirius entered
    into the popular consciousness.  A number of ancient authors, including
    Homer, Horace, Cicero, Seneca, and Ptolemy, have called Sirius red in
    their works.  Manilius, however, clearly called Sirius "blue-white" -
    its true color.

        Manilius also provided us with an outline of Roman Stoicism and
    Roman astrology.  Astronomy places a secondary role.

        In "The Astronomica", we uncover a different version and
    interpretation of ancient astronomical and astrological thought,
    rather than new knowledge.  If Manilius' work had not survived, little
    would have been lost.  This and his Latin have meant that his work
    have been little examined by classicists.  However, there are so few
    astronomical works surviving from the ancient world that each must be
    closely examined to wring from it what information we can.

        After Manilius there were few remaining classical astronomer of
    note until the surviving work of Ptolemy Claudius, circa 150 A.D..
    His work, while of questionable veracity and partly astrological,
    summarized the astronomy of the ancients and was the basis for
    Medieval Arabic astronomy.  Ptolemy's work was not superseded until
    Copernicus and Kepler.  The failures of Manilius as an astronomer in
    themselves tell us to what standing astronomy had declined from the
    earlier Greek period.  Manilius can at least reflect on the work of
    other, more prominent authors of his period.

        Based upon my investigations into Manilius, I feel that he was at
    least an active observer of the heavens.  His work, while not great in
    itself, has some merit and worthwhile information.  It represents a
    large expenditure of time and energy.  Its scope and complexity
    required many years of observation and composition.  His work also
    allows us to better measure the works of other classical scientific
    figures.

        Further Reading -

        General Discussions of Ancient Astronomy:

        A well quoted authority is A HISTORY OF ASTRONOMY, by A.
    Pannekoek, Interscience Publishers, Inc., 1961.

        A more exacting look at ancient astronomy comes from THE EXACT
    SCIENCES IN ANTIQUITY, by O. Neugebauer, 1957.

        A detailed look at the "scientific" era of ancient astronomy can
    be found in EARLY GREEK ASTRONOMY TO ARISTOTLE, by D. R. Dicks, Thams
    and London, 1970.

        For a "light" general text, look at ASTRONOMY OF THE ANCIENTS,
    edited by K. Brecher and M. Feirtag, MIT Press, 1980.

        For those interested in reading further on Greece and Rome:

        FROM SOLON TO SOCRATES, by Victor Ehrenberg, Methuen and Co.

        HISTORY OF ROME, by Michael Grant, Weidenfeld and Nicolson.

        An introduction to Stoic philosophy as it relates to astronomy
    can be found in THE STOIC TRADITION FROM ANTIQUITY TO THE EARLY MIDDLE
    AGES, Colish, ML., pub. E. J. Brill, 1985.

        For a description of the Epicurean scientific philosophy, read
    Lucretius' "De Rerum Natura", translated by W. Leonard, and S. Smith.

        For a critique of Ptolemy's work, read THE CRIME OF PTOLEMY
    CLAUDIUS, by R. Newton, The John Hopkins University Press, 1977.

        Related EJASA Article -

        "Astronomy in Ancient Mesopotamia", by Stacey Abrams - September 1991

        About the Author -

        Ian Bacon is a Masters student in Classics at the University of
    Western Australia.  His Master's topic is an examination of Manilius
    from an astronomical viewpoint.  Ian possess degrees in computer
    science, information technology, and Classics.  Ian has worked at
    the Perth (Australia) Astronomical Observatory and as a computer
    programmer.  Taking time to complete a Classics Masters is a long-
    term ambition of Mr. Bacon and one he thoroughly enjoys.

  =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
  Ian Bacon                          Department of Classics & Ancient History
  Masters Student                             University of Western Australia
  Email: [e-mail]                    Nedlands, Australia, 6009
  P.O. Box 166, Scarborough, Australia, 6019         fax:   [phone]
  [phone] (private mobile telephone)         voice: [phone]

    Disclaimer: "What, take my comments for those of the University?
                 Ha, ha, ha, ha, haaaaaaa!"

     "He will never amount to anything." - School report on Albert Einstein

  -=-=-=-=-=-=-=-=--------------------------------------------=-=-=-=-=-=-=-=-


                         PERSEIDS 1993: SHOWER OR STORM?

                                 by Peter Brown

            Courtesy of Paul Dickson ([e-mail]),
          Editor of the Saguaro Astronomy Club's newsletter, SACNews,
          in Phoenix, Arizona.

        After many years of speculation, the parent comet of the Perseid
    meteor stream returned to the neighborhood of the Sun in the last
    months of 1992.

        The original predictions for the comet placed its perihelion
    passage in the first years of the 1980s.  Much anticipation surrounded
    this event and many people reported noticeable increases in Perseid
    activity, particularly in 1980.  In all likelihood, the returns around
    1980 were ordinary.  The few observers who noted high activity became
    the "standard" quoted ZHRs (Zenith Hourly Rates) for many years and
    therefore a self-fulfilling prophecy developed with respect to high
    Perseid activity.  In addition, these years still saw vastly different
    methods of reduction and analysis of visual data, so that comparisons
    between different groups and even individuals with varying perceptions
    were unrealistic.

        The returns after 1980/1981 were generally quoted as weaker in
    activity in direct proportion to the interest in the stream and the
    belief that comet P/Swift-Tuttle had arrived unseen or not at all.
    Beginning in 1988, the International Meteor Organization (IMO)
    implemented global analysis of the stream using standardized reduc-
    tion techniques and from data with uniform collection parameters.
    Additionally, the IMO introduced computer-calculated ZHR procedures,
    allowing flexibility to researchers in choosing the methods of
    reduction and therefore permitting accuracy checks of the final
    results.  This initial global analysis produced a surprise:  A
    double maxima!

        The result was widely criticized, for the statistical significance
    of the new structure could not be objectively determined and the
    reduction procedures, though based on the best available techniques at
    the time, were still somewhat new.  The new peak appeared some twelve
    hours before the "normal" Perseid peak.  Initial explanations ranged
    from differences in perception between different groups of observers
    to a simple statistical "blip" in the data.  Considering that more
    than 53,000 meteors had been used in the analysis, the latter
    explanation seemed doubtful.

        Then the same double peak structure was found in the 1989 data at
    the same location, again separated by twelve hours from the primary
    "stable" maximum.  The data from 1989 were even higher quality than in
    1988, with about the same number of meteors.  The analysis techniques
    had been refined through experience with other shower global analysis
    and the conclusion seemed inescapable:  A double peaked structure for
    the Perseids existed.

        The double peak profile had not been conclusively observed
    previously and a few explanations for the structure were given.  The
    newer peak was felt to consist of younger particles than the main peak
    some twelve hours later (a conclusion that was to ultimately prove
    true).  The authors of the 1989 analysis speculated that the material
    might be from a passage of P/Swift-Tuttle in the early 1980s.

        The 1990 return was destroyed by the full phase of the Moon and
    no reliable analysis could be attempted with such bad data.  The next
    year, observers around Earth had been alerted to the possibility of
    enhanced activity due to the new peak some twelve hours before the
    main maxima.  In 1991, the new peak would favor observers in Japan -
    and favor them it did!  The Japanese observers witnessed one of the
    strongest displays of the Perseids in the last century with ZHRs over
    four hundred.  This was clearly stronger activity than had been
    witnessed in the past few returns and it seemed that the stream was
    changing.

        Shortly after the Japanese announced the heightened activity,
    Brian Marsden pointed out that in a paper he published in 1973 he
    discussed the possibility that P/Swift-Tuttle might actually return in
    1992 if it was the same comet observed in 1737.  While he had ranked
    the possibility as slight that the 1737 comet was P/Swift-Tuttle in
    1973, the enhanced Perseid display in 1991 revived the remote chance
    that the comet might return in 1992.

        The telling sign would be Perseid activity in 1992.  Unfortunately,
    a full Moon would compete with the meteor show and make data analysis
    very tricky.  As the data from the previous returns showed that Europe
    would be the best place to observe the early peak, much preparation was
    made there to capture the event.  Unfortunately, meteor showers - unlike
    eclipses - have an inherent unpredictability resulting from our lack of
    knowledge regarding the dust distribution about the parent comet.

        The 1992 display showed this maxim perfectly:  The new peak
    shifted some two to three hours earlier than what had been observed
    in past years.  As a result, Asian and Russian observers were in the
    best locations to witness the display.  After much analysis of the
    available observations, it appears that the 1992 activity was higher
    than in 1991, perhaps with a peak ZHR of order five hundred, though
    this peak value will remain highly uncertain due to the effects of
    lunar interference.

        This brings us to the next logical stage of the "act", the 1993
    display.  With P/Swift-Tuttle recovered shortly after the 1992 display
    (and with elements close to those predicted by Marsden in his 1973
    paper), it became apparent that the geometry between the comet and
    Earth could make the 1993 display very strong.  Indeed, our geometry
    with the comet is very similar to that between Earth and comet
    P/Tempel-Tuttle in 1833.  This is suggestive that a strong return is
    in store for observers in 1993.  However, P/Tempel-Tuttle is *not*
    P/Swift-Tuttle and the dust distribution about the latter is unknown.
    While there is much circumstantial evidence favoring a storm, nothing
    can be certain.

        Keeping these cautionary notes in mind, what might be predicted
    for 1993?  Based on the node of the comet and the maximum activity in
    1992, one would expect peak activity to be at 1 UT (Universal Time)
    on August 12, 1993.  Some have suggested that the shift in activity
    between the 1991 and 1992 displays suggest that we can expect another
    0.1 day advancement of activity in 1993, closer to 22 UT on August 11.
    While this is possible, I consider the shift unlikely.  Meteor storms
    usually occur very close to the node of their parent comet as the 1992
    display did relative to P/Swift-Tuttle.  Basing an estimate of this
    sort on two data points (the 1991 and 1992 maxima) is a bit question-
    able at least, so I see little reason to suppose a further 0.1 day
    shift will occur.

        What sort of display are we likely to encounter?  The past meteor
    storms for which reliable observational data exist suggest that newly
    ejected cometary material is rich in faint meteors.  This seems to be
    the best guess of what will be seen in 1993.  That is not to say that
    there will be little or no large particles encountered, but the
    proportion of faint meteors to bright meteors will be higher than in
    regular Perseid displays.  The central questions - how long will
    the display last and what will be the maximum activity - are very
    difficult to predict.  Meteor storms generally last for a few hours at
    most.  Some historical records suggest that large displays can carry
    on for days, but these records are very open to interpretation.  Data
    from more recent storms seems to suggest that several hours (two to
    six) are a good guess for the longest time for which unusually high
    activity might be observed.  The 1833 Leonids, for example, showed
    strong activity for nearly six hours.

        The peak rates are complete unknowns.  The largest meteor storms
    on record for the last few centuries produced activity on the order of
    100,000 meteors per hour for intervals shorter than about one hour.
    Ancient records do little to pin down peak rates of meteor storms
    earlier than about 1800.  Everyone's guess is equally valid in this
    instance.

        Whatever the 1993 display produces it will go down in history as
    one of the most waited for showers ever.

        The International Meteor Organization would be interested to
    receive your observations, whether you see unusual numbers of meteors
    or not.  Please follow the techniques outlined in the August 1993
    issue of SKY & TELESCOPE magazine and send the completed summaries
    to the addresses given therein.

        For readers in North America, the IMO may be contacted through the
    author, Peter Brown, North American Secretary - IMO, Dept. of Physics,
    University of Western Ontario, London, Ontario, N6A 3K7, Canada.
    (E-Mail - [e-mail])

        Readers outside North America should contact the Secretary-General
    of the IMO, Paul Roggemans, Pijnboomstraat 25, Mechelen, Belgium, B-2800

        Observations should be sent to:  Rainer Arlt, Berliner Strasse 41,
    D-O-1560, Potsdam, Germany (E-Mail - [e-mail])

        About the Author -

        Peter Brown is a graduate student in physics studying meteor

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End of Space Digest Volume 16 : Issue 693
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