From: klaes@verga.enet.dec.com (Larry Klaes)
Newsgroups: sci.astro,sci.space
Subject: Electronic Journal of the ASA - April 1992
Date: 7 Apr 92 23:36:41 GMT
Followup-To: sci.astro
Organization: Digital Equipment Corporation


                          THE ELECTRONIC JOURNAL OF
                  THE ASTRONOMICAL SOCIETY OF THE ATLANTIC

                       Volume 3, Number 9 - April 1992

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                              TABLE OF CONTENTS

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          * ASA Membership and Article Submission Information

          * The 179th Meeting of the American Astronomical Society (AAS): 
            A Volunteer's View - Ingrid Siegert-Tanghe

          * The Partial Eclipse of March 22, 1992 - Tom Polakis

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

                         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
    to the advancement of amateur and professional astronomy and space
    exploration, as well as the social and educational needs of its members.

        ASA membership application is open to all with an interest in
    astronomy and space exploration.  Members receive the Journal of the
    ASA (hardcopy sent through United States Mail - Not a duplicate of this
    Electronic Journal) and the Astronomical League's REFLECTOR magazine.
    Members may also purchase discount subscriptions to ASTRONOMY and
    SKY & TELESCOPE magazines.

        For information on membership, you may contact the Society at any
    of the following addresses:

        Astronomical Society of the Atlantic (ASA)
        c/o Center for High Angular Resolution Astronomy (CHARA)
        Georgia State University (GSU)
        Atlanta, Georgia  30303
        U.S.A.

        asa@chara.gsu.edu

        ASA BBS: (404) 985-0408, 300/1200/2400 Baud.

        or telephone the Society Recording at (404) 264-0451 to leave your
    address and/or receive the latest Society news.

        ASA Officers and Council -

        President - Don Barry
        Vice President - Nils Turner
        Secretary - Ingrid Siegert-Tanghe
        Treasurer - Mike Burkhead
        Directors - Bill Bagnuolo, Eric Greene, Tano Scigliano
        Council - Bill Bagnuolo, Bill Black, Mike Burkhead, 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
    Larry Klaes, EJASA Editor, at the following net addresses or the above
    Society addresses:

        klaes@verga.enet.dec.com
        or - ...!decwrl!verga.enet.dec.com!klaes
        or - klaes%verga.dec@decwrl.enet.dec.com
        or - klaes%verga.enet.dec.com@uunet.uu.net

        You may also use the above addresses for EJASA back issue requests,
    letters to the editor, and ASA membership information.

        When sending your article submissions, please be certain to include
    either a network or regular mail address where you can be reached, a
    telephone number, and a brief biographical sketch.

        DISCLAIMER -

        Submissions are welcome for consideration.  Articles submitted,
    unless otherwise stated, become the property of the Astronomical
    Society of the Atlantic, Inc.  Though the articles will not be used for
    profit, they are subject to editing, abridgment, and other changes.
    Copying or reprinting of the EJASA, in part or in whole, is encouraged,
    provided clear attribution is made to the Astronomical Society of 
    the Atlantic, the Electronic Journal, and the author(s).  Opinions
    expressed in the EJASA are those of the authors' and not necessarily
    those of the ASA.  This Journal is Copyright (c) 1992 by the
    Astronomical Society of the Atlantic, Inc.


         THE 179TH MEETING OF THE AMERICAN ASTRONOMICAL SOCIETY (AAS): 
                              A VOLUNTEER'S VIEW

                           by Ingrid Siegert-Tanghe

        The 179th meeting of the American Astronomical Society (AAS)
    was held in Atlanta, Georgia on January 12-15, 1992 at the Marriot
    Marquis hotel.  For the 1,247 astronomers who attended, the meeting
    was an opportunity to present their latest discoveries and research
    to their colleagues and the world.  For the ASA members and students
    who volunteered their help during the meeting, it was an opportunity
    to hear about the astronomers' exciting work first hand and rub
    shoulders with some of the great astronomers of our time.  Over
    thirty-five Society members took part, either as Georgia State
    University (GSU) organizers or as amateur volunteers.

        The news briefs which follow are a combination of press releases
    and the notes I took at the press conference.  In some cases I will
    directly quote the press releases and identify the sources.  There
    is much information to pass on.  In this article I will report on
    the major AAS announcements.  In a later article I will cover other
    celestial discoveries and some interesting research that is currently
    being conducted.

        Pulsars, Planets, and Neutron Stars -

        The announcement in July of 1991 by Dr. Andrew Lyne and his
    colleagues of the Jodrell Bank radio observatory in England of 
    their discovery of planets around the pulsar PSR 1829-10 rocked the
    astronomical world.  At the AAS meeting, Dr. Lyne announced that their
    findings were in error.  They had failed to compensate for slight
    variations in Earth's orbital motion around the Sun.  When this was
    taken into account, Dr. Lyne said the "planet just evaporated." 

        In a letter to the British journal NATURE, Dr. Lyne said,
    "Although there is no planet orbiting PSR 1829-10, pulsar timing
    remains the most sensitive technique for detecting planets outside 
    the solar system." 

        Another discovery of planets beyond our solar system was announced
    on January 9 in the journal NATURE.  By timing the arrival of radio
    signals from a rapidly spinning pulsar to the Arecibo Observatory's
    radio/radar telescope in Puerto Rico, Alexander Wolszczan and Dale
    Frail have found the strongest evidence so far for a planetary system
    outside our own:  Two or possibly three planets that orbit the neutron
    star PSR1257+12. 

        Dr. Wolszczan discussed their findings in further detail at the
    AAS meeting, noting that they had double-checked the pulsar's position
    and the timing of radio fluctuations, ruling out the mistakes made by
    Dr. Lyne. 

        A long series of observations that Wolszczan made between July of
    1990 and November of 1991 revealed the following information about the
    pulsar and its apparent planetary system: 

        "PSR1257+12 is an old pulsar, with more than one billion years
    having elapsed since it and a binary companion were formed as ordinary
    stars, out of a gravitationally contracting interstellar cloud.  Some
    10 million years after the binary formation, the more massive of the
    pair underwent a supernova explosion and its collapsed core became a
    neutron star."

        Further evolution of the remaining stellar companion caused
    accretion of some of its expanding envelope onto the neutron star. 
    This process helped to spin the pulsar up to a 6.2 millisecond
    rotation period observed today.  The companion itself probably had
    been vaporized by the pulsar's high energy radiation and supplied
    material for a formation of planets that are now seen orbiting
    PSR1257+12. 

        Two planets are orbiting PSR1257+12 about 53.6 million and 69.92
    million kilometers (33.5 million and 43.7 million miles) from the 
    pulsar, about the same distance that Mercury is from the Sun.  Both 
    are moving in nearly circular orbits, taking 66.6 and 98.2 Earth days 
    to complete each revolution. 

        A detailed analysis of the observations made to date suggest 
    the existence of one more planet circling the pulsar about 1.1
    Astronomical Units (AU) away and with an orbital period close to 
    one Earth year. 

        The newly discovered planets' masses are greater than that of
    Earth, at about 2.8 and 3.4 masses.  "In principle, they are massive
    enough to retain atmospheres.  But it is likely that any atmosphere
    would be blown away by the pulsar wind," Wolszczan said.  In density,
    composition, and size, these planets may be not unlike Earth or Venus.

        Responding to the gravitational pull of its planets, PSR1257+12 
    is wobbling in space.  It is that wobble which affected the precisely
    measured arrival times of pulsar signals at the Arecibo telescope and
    allowed the detection of the planets. 

        Dr. Wolszczan said that a few more years of observation will be
    required for absolute proof.  Dr. Frederic Rasio and his colleagues
    from Cornell University believe they can supply the proof fairly soon.
    The Cornell astronomers point out that, if the interpretation of the
    observations in terms of orbiting planets is correct, then additional
    perturbations corresponding to the mutual gravitational interactions
    between the planets themselves should be present in the data of
    Wolszczan and Frail. 

        Dr. Marco Tavani of the Institute of Geophysics and Planetary
    Physics at Lawrence Livermore National Laboratory presented a theory
    to the AAS on the formation of planets orbiting millisecond pulsars. 
    The new theory explains that the newly discovered planets may be 
    the final remnants of a companion star completely vaporized by the
    pulsar's energetic radiation.  Planetary formation can occur in two
    different ways.  According to the first scenario, the planets form
    after the pulsar has been created and has begun to vaporize its
    companion by irradiation.  According to the second scenario, there is 
    a binary star system evolving into an isolated millisecond pulsar, and
    the planets form when the neutron star is receiving matter from and
    being "spun-up" by its companion.  In both cases, the vaporized
    material can produce a gravitationally-bound disk of matter from 
    which planets can form. 

        Cornell University News Service, NATURE, THE NEW YORK TIMES, 
    Dr. Marco Tavani

        Wisconsin Scientists Discover a Hot Spot on a Pulsar -

        Scientists from the University of Wisconsin-Madison reported the
    discovery of a pulsar with a "hot spot" on its surface, a finding that
    seems to pinpoint the source of the distinctive pulsations of energy
    that give pulsars their name. 

        Using the X-ray satellite ROSAT to measure the surface temperature
    of a nearby pulsar, astrophysicists John P. Finley, Hakki Ogelman, and
    Umit Kiziloglu found a hot patch on the star that swept through the
    satellite's line of sight once every rotation. 

        The pulsar in question, according to Finley, is an unnamed pulsar
    situated just 1,500 light years from Earth.  Smaller that Manhattan
    Island, the pulsar has a hot spot on its surface which is about four
    percent hotter than the rest of the surface of the star. 

        The X-rays emitted by the star are higher in energy at precisely
    the same time the pulsed X-ray emission is greatest.

        "The whole star is glowing with X-rays and when you see this hot
    spot, your counts go up," Finley said.  "We can't say for certain that
    the radio beacon is coincident with the hot spot, but it's certainly a
    reasonable assumption to make." 

        University of Wisconsin-Madison News and Information Service

        First Supernova of 1992 -

        Supernova 1992A was discovered on January 10 by William Liller 
    of Vina del Mar in Chile.  Scientists at NASA's Goddard Space Flight
    Center (GSFC) confirmed the observation on January 13 with the
    International Ultraviolet Explorer (IUE) satellite.  Astrophysicist 
    George Sonneborn directed the pointing of IUE from Atlanta while 
    attending the AAS meeting. 

        The Type Ia supernova had a visual brightness of 12.8 magnitude
    when it was discovered.  It is located in the spiral galaxy NGC 1380
    in the constellation Fornax. 

        Cosmic Dark Matter Mapped -

        Dr. J. Anthony Tyson et al announced that they have been able to
    map the invisible cosmic "dark matter" in many giant clusters of
    galaxies. 

        The Universe is thought to contain much more dark matter than
    stars and gas.  The significance of this latest research is that it 
    is now possible to directly map the dark matter concentrations.  The
    image warping of background galaxy images due to the gravitational
    pull of the foreground dark matter is used to reconstruct a fuzzy
    picture of the dark matter. 

        Hubble Space Telescope (HST) Investigations -

        Black Hole in M87:  Astronomers report that they have found
    evidence that a black hole weighing over 2.6 billion times the mass 
    of the Sun exists at the center of the giant elliptical galaxy M87.
    Images from HST show that stars become strongly concentrated towards
    the center of the galaxy, as if drawn into the center and held there
    by the gravitational field of a massive black hole.  The results were
    reported by Dr. Tod R. Lauer of the National Optical Astronomy
    Observatories to the AAS meeting. 

        Early in the Twentieth Century astronomers discovered a gigantic
    jet of plasma being ejected out of the M87 nucleus.  The jet and
    nucleus were found to emit strong radio and X-ray radiation.  The
    cause of this activity remained a mystery until the HST observations. 

        HST has revealed the density of stars in M87 increases abruptly
    toward the core.  It is, in fact, five hundred times denser than
    thought from ground observations.  Stars once freely orbiting in and
    out of the M87 core are being gradually pulled toward the center and
    then into orbits closely bound to the black hole.  The whole core of
    the galaxy thus smoothly collapses inward, and the density of stars
    near the very center becomes extreme. 

        High resolution spectra from HST will confirm with certainty the
    existence of the black hole.  This will unfortunately have to wait
    until HST is repaired.  Dr. Lauer is convinced that this is a black
    hole, but is reluctant to state with certainty its existence until all
    the tests have been performed.  "It looks like a duck but we haven't
    heard it quack yet," he observed. 

        Planetary Nebula in the Large Magellanic Cloud:  HST has imaged
    N66, a planetary nebula in the Large Magellanic Cloud.  The image 
    was obtained at 10:41 EDT on June 26, 1991, using the European Space
    Agency's (ESA) Faint Object Camera (FOC).  This is the first time a
    planetary nebula has ever been seen so clearly in a galaxy beyond our
    own Milky Way.  N66 is located 169,000 light-years from Earth.  The
    FOC image reveals complex details as small as 0.1 arcseconds.  The
    nebula was ejected by a luminous red giant star, which subsequently
    contracted to form a blue remnant star. 

        NGC 1275 Star Clusters:  Dr. Jon Holtzman of Lowell Observatory
    announced the discovery of fifty bright, young massive globular
    clusters at the center of NGC 1275.  Holtzman and his colleagues were
    observing this galaxy in Perseus because of its peculiarities observed
    from the ground.  What they discovered was another strange feature. 
    Globular clusters are among the oldest objects in the Universe.  To
    find the blue, young clusters in the center was a surprise. 

        NGC has such a peculiar shape, some astronomers previously have
    suspected that it may actually be two galaxies - a giant elliptical
    galaxy and a smaller spiral galaxy - passing through one another. 
    Holtzman suggests that the clusters may have formed as a result of
    just such a merger or collision. 

        NGC 1275 lies at the heart of the Perseus cluster of galaxies, a
    rich collection of more than five hundred galaxies.  The galaxy is
    surrounded by a luminous halo of hot gas, which glows in X-rays. 
    Gravity pulls this superheated gas into the galaxy as a "cooling
    flow", which produces filaments.  This cooling, condensing gas might
    also produce newborn stars. 

        Space Telescope Science Institute

        Coming soon:  More AAS reports containing exciting investigations
    of gamma-ray bursts, supernovae, binary pulsars, the Pleiades star
    cluster, and the origin of the Universe. 

        About the Author -

        Ingrid Siegert-Tanghe is Secretary to the Astronomical Society of
    the Atlantic and past (as well as present) member of the Louisville
    Astronomical Society, where she served in several officer positions.
    Her interests are computer-controlled telescopes and learning more
    about the science of astronomy. 


                    THE PARTIAL ECLIPSE OF MARCH 22, 1992

                               by Tom Polakis

        There was only one message on my telephone answering machine 
    when I got home at eleven p.m. on Saturday, March 21.  It was Pierre
    Schwaar's voice from three hours earlier, inviting me over to watch 
    a partial eclipse of a moon.  Not Earth's moon, but Ganymede, the 
    largest of Jupiter's four Galilean satellites.

        The circumstances were such that the relatively tiny shadow of 
    the smallest Galilean moon, Europa, was to be cast onto the surface of
    Ganymede at 1:00 the next morning.  Having seen another in a series of
    weekend downpours earlier that day, and knowing that I was going to be
    viewing with Mr. Pierre Schwaar - that magnetic attractor of clouds -
    it took a lot of contemplation before deciding that it was worth the
    trip to his house in Phoenix, Arizona. 

        Sure enough, when I arrived, hanging overhead was what seemed to
    be an endless stream of mid-level clouds which Pierre claimed were
    forming over his backyard.  We had intermittent views of the giant
    Jovian planet before the event began through Jim Stevens' binocular
    viewer on Pierre's fifty-centimeter (twenty-inch) telescope.  After
    tweaking the collimation on his viewer, Jim was able to convince me
    in no time how much better the planet looked when viewed through both
    eyes.  The seeing conditions were decent enough to easily show the
    difference in size between the disks of Europa (one arcsecond) and 
    Ganymede (1.7 arcseconds).  Ganymede shone almost a magnitude brighter 
    than Europa, about ten arcseconds further out from Jupiter. 

        For the first one-half hour of the eighty-minute event, the clouds
    got the better of us.  What appeared to be a clearing line never
    materialized - Pierre was going to miss yet another eclipse!  Finally,
    however, the cloud show finally abated and we were treated to an
    unforgettable sight.  The atmosphere was now steady enough to show
    that something was definitely 'wrong' with Ganymede's disk.  It was
    no longer round but appeared to show an oval form.  Looking closer 
    still at over 300x with his fifty-centimeter stopped down to forty
    centimeters (sixteen inches), Pierre claimed to be seeing the actual
    "bite" out of the satellite's disk.  Jim verified this claim and even
    identified that the bite was taken out of the northern hemisphere of
    the moon. 

        After a prolonged look, I finally saw the 'kidney bean' shape of
    Ganymede.  This became clearer as the seeing improved, and for the
    next twenty minutes we watched as the shadow receded from the disk 
    of Ganymede.  Viewing at a similar magnification with the conventual
    monocular view, the spectacle was not nearly as obvious.  The only
    apparent feature at mid-eclipse was the brightness of Ganymede, which
    had dropped to approximately that of Europa. 

        This event showed us what can be seen by pushing high resolution
    observing to its limit.  There will not be many more of these satel-
    lite phenomena left in this series for several years, as the orbital 
    plane geometry of the moons becomes unfavorable.  Probably the high-
    light of the event was that, after a daunting string of cloudouts,
    Pierre finally did get to see an eclipse.  It was of a two-arcsecond
    Galilean moon, but at least it was an eclipse. 

        Related EJASA articles -

        "The Ice Moons of the Jovian Worlds", by Craig M. Levin - March 1990 

        "Viewing Jupiter's Galilean Moons with the Unaided Eye", by Alan 
         William Paeth - July 1990 

        About the Author -

        Tom Polakis is member of the Saguaro Astronomy Club (SAC).  Tom 
    is an avid amateur astronomer currently residing in Mesa, Arizona.  
    He has had articles and photographs published in such magazines as 
    SKY & TELESCOPE, ASTRONOMY, and DEEP SKY. 

        Tom's E-mail address is:  70413.1543@compuserve.com


      THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC

                          April 1992 - Vol. 3, No. 9

                           Copyright (c) 1992 - ASA