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Subject: SPACE Digest V10 #410

SPACE Digest                                     Volume 10 : Issue 410

Today's Topics:
        Electronic Journal of the ASA, Vol. I, No. VI
----------------------------------------------------------------------

Date: 8 Jan 90 18:15:59 GMT
From: mephisto!eedsp!chara![e-mail]  (Donald J. Barry)
Subject: Electronic Journal of the ASA, Vol. I, No. VI


                        THE ELECTRONIC JOURNAL OF
                THE ASTRONOMICAL SOCIETY OF THE ATLANTIC

                    Volume 1, Number 6 - January 1990

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

                            TABLE OF CONTENTS

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

         * ASA Membership Information

         * Long-Term Trends in Ground-Based Astronomy

             - Interview with Dr. Hal McAlister by Edmund G. Dombrowski

         * Total Solar Eclipses for the Nineteen Nineties - Philip Taylor

         * Explaining Solar and Lunar Eclipses - Brent Studer

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

                       ASA MEMBERSHIP INFORMATION

         The Electronic Journal of the Astronomical Society of the Atlantic
    is published monthly by the Astronomical Society of the Atlantic, Inc.
    The ASA is a non-profit organization dedicated to the advancement of
    amateur and professional astronomy and space exploration, and to the
    social and educational needs of its members.

         Membership application is open to all with an interest in
    astronomy and space exploration.  Members receive the ASA Journal
    (hardcopy sent through U.S. Mail), the Astronomical League's REFLECTOR
    magazine, and may additionally purchase discount subscriptions to
    SKY & TELESCOPE, ASTRONOMY, DEEP SKY, and TELESCOPE MAKING magazines.

         For information on membership, contact the Society at:

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

         or use the ASA network address at:

          [e-mail]

         or telephone the Society recording at [phone]

         ASA Officers and Council -

         President - Don Barry
         Vice President - Bill Bagnuolo
         Secretary - Ken Poshedly
         Treasurer - Alan Fleming
         Board of Advisors - Bill Hartkopf, Edward Albin, Jim Bitsko

         EJASA Editor - Larry Klaes
         Observatory Co-Chair - Michael Wiggs, Max Mirot
         Observing Coordinator - Eric Greene
         Georgia Star Party Chairman - Patti Provost
         Advertising Committee - Paul Pirillo
         Community Coordinator - Becky Long
         Regional Planetary Society Coordinator - Jim Bitsko
         Society Librarians - Julian Crusselle, Toni Douglas

         Telephone the Society Info Line at [phone] for the
    latest ASA News and Events.

         ARTICLE SUBMISSIONS -

         Article submissions on astronomy and space exploration to
    the EJASA are most welcome.  Please send your on-line articles to
    Larry Klaes, EJASA Editor, at the following net addresses:
    [e-mail], or ...!decwrl!wrksys.dec.com!klaes,
    or [e-mail], or [e-mail],
    or [e-mail]

         If you cannot send your articles to Larry, please submit them
    to Don Barry, ASA President, at the following net addresses:
    [e-mail], or chara![e-mail], or [e-mail]

         You may also use the above net addresses for EJASA backissue
    requests and ASA membership information.

         Please be certain to include either a net or U.S. 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, and although they will not be used for profit,
    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).  This Journal is Copyright
    (c) 1990 by the Astronomical Society of the Atlantic.


                  LONG-TERM TRENDS IN GROUND-BASED ASTRONOMY

         an interview with Dr. Hal McAlister by Edmund G. Dombrowski

        In light of the U.S. re-entry into manned spaceflight with the
    1988 flight of the DISCOVERY Space Shuttle mission, I, and I am sure
    many others, am looking forward to the eventual launch and deployment
    of the Hubble Space Telescope into Earth orbit.  Currently scheduled
    for launch in late March of 1990, the HST represents a new link in
    astronomical history, a move towards the advent of full range
    "satellite" observatories.  When the telescope is activated, we can
    expect to look further back in time, down to visual magnitudes limited
    only by the size of the aperture, avoiding cutoffs due to atmospheric
    interference.  We can also expect to do high resolution imaging of
    objects previously considered too faint to observe from any ground-
    based observatory, and be able to cover a large range of observations
    throughout the entire electromagnetic spectrum.  These are only a few
    of the many advantages the Space Telescope has to offer, which will
    hopefully provide us with an abundance of data to be analyzed in the
    Nineteen Nineties and beyond.

        However, what is the long term prognosis for the Space Telescope
    and other similar orbital astronomical facilities?  Can we maintain
    such facilities within the expected NASA budget, or will other
    projects undergo major cuts to supplement our space needs?  And what
    about ground-based astronomy?  Will we continue to put time and money
    into the development of improved astronomical observatories throughout
    the world, or slowly de-emphasize our ground-based efforts overall?
    These are indeed important questions to be answered for the professional
    as well as the amateur astronomer, and hence prompted me to conduct an
    interview with someone in touch with these issues.  The person I sought
    out was Dr. Hal McAlister of Georgia State University.

        Dr. McAlister is a professor in the department of physics and
    astronomy at Georgia State University.  His experience is well grounded
    since he has served on numerous committees dealing with these issues,
    most notably the National Science Foundation (NSF) Astronomy Advisory
    Committee on which he served from 1983 throughout 1986.  Also to his
    credit was his election to the Vice Presidency of the International
    Astronomical Union (IAU) Commission 26 in November of 1985, and to
    the Presidency of the same commission in September of 1987.  However,
    perhaps more pertinent to the subject at hand, Dr. McAlister served on
    the National Optical Astronomy Observatories (NOAO) Committee charged
    with reviewing the site selection for the National New Technology
    Telescope in 1986, and has been a member of the NASA Technology Working
    Group on Optical Imaging Interferometry in Space throughout 1987.  His
    experience covers a broad range of topics in both ground-based astronomy
    as well as developmental studies of astrophysical facilities in space.

        Dr. McAlister began by informing me that perhaps the most important
    issue at hand of space versus ground-based astronomy is simply the cost.
    It is well known that any project researched and developed for orbital
    use in space will be at an exorbitant price.  He pointed out that it
    would cost approximately "two billion dollars to build a 2.5-meter
    (100-inch) telescope for space, whereas it would cost only 4.5 million
    dollars for the same telescope at a ground-based facility."  In his
    opinion, we would be abandoning a lot of good, worthwhile astronomical
    projects that could be done on the ground if we chose to spend most of
    the available budget towards developing expensive satellite observatories.
    There would be no point in concentrating all our efforts solely towards
    the advancement of space astronomy since it would be less expensive and
    more beneficial for the entire astronomical community to continue
    developing ground-based facilities.

        Dr. McAlister envisions a future involving a healthy balance
    between the two alternative modes of research.  He sees a need for an
    extension into space, but not at the risk of impairing already existing
    programs.  Projects similar to that of the Hubble Space Telescope are
    indeed necessary, according to McAlister, because of the need to
    constantly increase our knowledge of the Universe, especially in areas
    of astronomical research not attainable by the use of ground-based
    facilities.  In fact, in his view, the main advantage of the Space
    Telescope will be its use as a cosmological probe.  This instrument,
    as mentioned earlier, will be able to do high resolution imaging down
    to extremely faint magnitudes.  We are presently able, via speckle
    interferometry and other interferometric techniques, to make use of
    upper atmospheric turbulence to increase our resolution of systems
    normally cutoff by telescope and magnitude limitations.  With the
    Space Telescope, we will be able to observe astrophysical objects
    at magnitudes even fainter than what these existing ground-based
    techniques can achieve.

        But what is in store for the future of already existing facilities
    in the United States and abroad?  And what is on the proverbial
    drawing board in terms of new developments for astronomical
    observatories?  Dr. McAlister informed me that there is an Astronomy
    Survey Committee currently being organized by the National Academy of
    Science to establish goals for ground-based astronomy for the 1990s.
    The committee prepares a report based on a ten year study.  There is
    one currently in preparation for the upcoming decade.  In his opinion,
    the next report will "set large telescope arrays at a high priority,"
    that is, systems of "twelve or more telescopes of 4 to 8 meters (160
    to 320 inches) in diameter costing hundreds of millions of dollars to
    develop."  He believes that there will be a major move in ground-based
    astronomy emphasizing larger arrays which would employ higher
    resolution techniques.  In radio astronomy, we will focus our efforts
    towards building high resolution observatories at shorter wavelengths.
    There will be a "push for millimeter wavelength arrays," according to
    McAlister, and, as far as optical observatories are concerned, he sees
    the U.S. shifting from its original plan of building extremely large
    single telescopes to concentrating on systems of telescopes, since the
    Europeans have made a major financial commitment to their VLT and we
    have postponed our efforts in developing the NNTT.

        None of these trends are absolute, but the nature of a cost
    effective approach in the 1990s points towards such programs.  In
    McAlister's own words, "Astronomy in space will always be more
    expensive than its ground-based counterpart," and he therefore
    believes that there will be an eventual deemphasis placed upon future
    projects since the incentives will be far outweighed by the cost.  As
    far as other satellites scheduled for deployment are concerned, such
    as the Advanced X-ray Astrophysics Facility (AXAF), it remains to be
    seen if they will be successful enough to promote successive programs.

        In addition to being a professor at Georgia State University since
    1977, Dr. Hal McAlister is also the director of the Center for High
    Angular Resolution Astronomy (CHARA), a research group dedicated to
    the applications of speckle interferometry.  The group is currently
    involved in the development of a long-baseline optical interferometer,
    the CHARA array, which would consist of seven one-meter (3.3-foot)
    telescopes appropriately positioned in a Y configuration with baselines
    reaching up to 200 meters (660 feet).  The system would make use of
    telescope pairs, combining beams to increase resolution.  If implemented,
    this optical array would be among the first of its kind in the U.S. and
    would certainly be a major factor in the continual development of
    ground-based astronomy.

        About the Author -

        Edmund Dombrowski is pursuing advanced study in Astronomy under
    Hal McAlister at the Center for High Angular Resolution of Georgia
    State University.  His professional interests include speckle
    interferometry, photometry, and the Hyades distance scale.


                TOTAL SOLAR ECLIPSES FOR THE NINETEEN NINETIES

               by Philip Taylor, Brighton Astronomical Society

        Editor's Note:  The July 11, 1991 total solar eclipse across
    Mexico, for which the ASA will mount an expedition, is the best of
    a number of such upcoming eclipses.  Below is the entire list of
    total solar eclipses through the end of the Twentieth Century.

        Data obtained from Jean Meuus' CANON OF SOLAR ECLIPSES:

        1990 - July 22:  Maximum duration 2 minutes, 33 seconds.

        The first European total solar eclipse in several decades.
    The eclipse track will begin in Finland and track eastward across
    the Soviet Union.

        1991 - July 11:  Maximum duration 6 minutes, 54 seconds.

        The eclipse will start in the Pacific Ocean over the Hawaiian
    Islands and head east, where it will skim western Mexico and sweep
    into South America.  The eclipse will be seen as partial throughout
    most of North America.

        1992 - June 30:  Maximum duration 5 minutes, 20 seconds.

        A long track of totality that manages to avoid land completely!
    Crosses the South Atlantic Ocean and ends just off the east coast of
    Argentina.  Not a good viewing bet, as the weather will probably be
    less than favorable (their mid-winter), even if you do sail to the
    eclipse track.

        1993:  None.

        1994 - November 3:  Maximum duration 4 minutes, 23 seconds.

        The track goes across South America, which includes South Brazil,
    North Argentina, Bolivia, and North Chile.  Possibly some reasonable
    weather.

        1995 - October 24:  Maximum duration 2 minutes, 10 seconds.

        A long land track running from Afghanistan through Northern India
    and Southeast Asia (including Thailand).  The India area looks good,
    with the eclipse in an accessible area in the north (including the
    Ganges Valley and Calcutta area), and reasonable weather prospects -
    this is after their monsoon season.  I would guess this eclipse track
    is more heavily populated than any other during the Nineteen Nineties.

        1996:  None.

        1997 - March 9:  Maximum duration 2 minutes, 50 seconds.

        Not very favorable for viewing - East Siberia only.

        1998 - February 26:  Maximum duration 4 minutes, 8 seconds.

        A long equatorial track from the Central Pacific Ocean, over
    Northern Colombia and Venezuela, across the Caribbean, and ending up
    right across the Atlantic Ocean near the Canary Islands.  The eclipse
    track may pass very close to the Caribbean Islands of Martinique
    and/or Dominica.

        1999 - August 11:  Maximum duration 2 minutes, 23 seconds.

        The third European total solar eclipse since 1961 and 1990, and
    the first in Great Britain since 1927.  Crosses Cornwall County in
    southwest England, then across North France (just north of Paris),
    Germany (Bavaria), Austria, Hungary, Rumania, Bulgaria, through the
    Black Sea to Turkey, then off across Syria to end up in India.  There
    will probably be millions traveling across Europe to see this totality:
    In Cornwall they are said to already be taking hotel bookings!  For a
    combination of good weather and accessibility (from Europe at least),
    the Turkish Black Sea coast - east of Istanbul - is a good bet.
    Weather prospects are pretty grim for England and North France.

        For more details on upcoming solar and lunar eclipses, consult
    such astronomy periodicals as ASTRONOMY and SKY & TELESCOPE.

        About the Author -

        Philip Brighton is a past newsletter editor of the Brighton
    Astronomical and Scientific Society, and a regular amateur
    astronomer on USENET.


                     EXPLAINING SOLAR AND LUNAR ECLIPSES

                               by Brent Studer

        Eclipses are one of the most impressive events in the field of
    astronomy, and have inspired awe and fear in humanity for thousands of
    years.  The following are some brief definitions and descriptions of
    how the Sun can be "covered" by the Moon as seen from Earth, and why
    Earth's shadow can in turn fall upon the Moon:

        Line of nodes - The line through the center of Earth that connects
    the nodes of the Moon's orbit.  The nodes are the points in the Moon's
    orbital path around Earth that cross the plane of the ecliptic.

        Eclipse season - The times of the year (about six months apart)
    when the Earth-Sun line is approximately along the line of nodes.
    Only at these times can eclipses occur.

        Ecliptic limits - Relaxation of the strict linear geometry, due to
    the fact that the three bodies involved - Sun, Earth, and Moon - are
    not point objects.  They do not have to be in an exact straight line
    for eclipses to occur.

        The ecliptic limits are variable quantities since they depend on
    the exact angular sizes of the Sun and the Moon in the sky (and hence
    their exact distances from Earth), and on the exact inclination of the
    Moon's orbit to the ecliptic.  If the extreme range of the values are
    used, it is possible to determine the largest and smallest values of
    the ecliptic limits.  The smallest value, or minor solar ecliptic
    limit, is slightly more than fifteen degrees.

        During one synodic month, the angular distance the Sun moves along
    the ecliptic is roughly 29 degrees.  Therefore, between two successive
    New Moons, the Sun moves less than twice the minor ecliptic limit (29
    < 2 x 15).  So, it is impossible for the Sun to pass through a node
    without at least one eclipse during an eclipse season (it will be a
    solar eclipse).  This means there must be at least two solar eclipses
    (either partial or total) during one calendar year.

        If the Sun is eclipsed within a day or two after reaching the
    western edge of the ecliptic limit, a second solar eclipse can occur
    at the next New Moon, just prior to the end of that eclipse season.
    Now, if the first eclipse season occurs in January, the next eclipse
    season will be six months later (with another solar eclipse and
    possibly a lunar eclipse occurring), followed by a repeat of the first
    eclipse season in December.  Thus, we arrive at a maximum number of
    solar eclipses in one calendar year of five.  This event last occurred
    in 1935.

        Lunar eclipses occur about as frequently as solar eclipses, if we
    include the penumbral eclipses, which are difficult to observe.  The
    number of lunar eclipses that may occur each year varies from two to
    five.

        Because penumbral lunar eclipses are barely noticeable, the number
    of observable solar eclipses outnumber observable lunar eclipses by
    about 33 percent.  Lunar eclipses are, however, more common for a
    given location, since they can be viewed from more than half of Earth,
    and solar eclipses are visible only over a limited region.

        Given the values of the ecliptic limits for both types of
    eclipses, it is possible to arrive at a maximum number of eclipses in
    one calendar year of seven.  To prove this, one would have to use the
    minor lunar ecliptic limit of 9.5 degrees and the same arguments used
    above; unfortunately, this is difficult to show without the benefit of
    a few simple diagrams and some simple calculations.

        Due to the fact that the minor lunar ecliptic limit is so small
    compared to the Moon's angular motion along the ecliptic in one month,
    there can be at most one lunar eclipse per eclipse season.  Since it
    has already been stated that there may be two solar eclipses in one
    season, the number of solar eclipses in one calendar year will
    outnumber lunar eclipses.

        An important note about eclipse observing:  Observing a solar
    eclipse can be dangerous to your eyes - NEVER look directly at the
    Sun, particularly through unfiltered telescopes or binoculars.  One
    alternate method for observing a solar eclipse is to project the image
    of the Sun onto a piece of white cardboard, either through a telescope
    or through a small hole cut into another piece of cardboard, but it is
    highly suggested that even this viewing method should be done with
    caution and experience.  Lunar eclipses, by comparison, are quite safe
    to observe directly, either with the unaided eye or through optical
    instruments.

        About the Author -

        Brent Studer is an amateur astronomer who occasionally
    contributes to USENET.


     THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC

                       January 1990 - Vol. 1, No. 6

                         Copyright (c) 1990 - ASA


--
Donald J. Barry       [phone]         | [e-mail]
Center for High Angular Resolution Astronomy | President, Astronomical
Georgia State University, Atlanta, GA 30303  | Society of the Atlantic

------------------------------

End of SPACE Digest V10 #410
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