Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from sushi.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Thu, 11 Jan 90 01:35:07 -0500 (EST) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Thu, 11 Jan 90 01:35:00 -0500 (EST) 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!don@rutgers.edu (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: asa%chara@gatech.edu or telephone the Society recording at (404) 264-0451 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 (404) 264-0451 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: klaes@wrksys.dec.com, or ...!decwrl!wrksys.dec.com!klaes, or klaes%wrksys.dec@decwrl.dec.com, or klaes@wrksys.enet.dec.com, or klaes%wrksys.enet.dec.com@uunet.uu.net If you cannot send your articles to Larry, please submit them to Don Barry, ASA President, at the following net addresses: don%chara@gatech.edu, or chara!don@gatech.edu, or don@chara.UUCP 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 (404) 651-2932 | don%chara@gatech.edu Center for High Angular Resolution Astronomy | President, Astronomical Georgia State University, Atlanta, GA 30303 | Society of the Atlantic ------------------------------ End of SPACE Digest V10 #410 *******************