Date: Fri, 6 Nov 92 05:05:52 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #385 To: Space Digest Readers Precedence: bulk Space Digest Fri, 6 Nov 92 Volume 15 : Issue 385 Today's Topics: astronauts voting Electronic Journal of the ASA (EJASA) - November 1992 Thanks for the help! the Happyface on Mars Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: Thu, 5 Nov 1992 20:21:48 GMT From: Leigh Palmer Subject: astronauts voting Newsgroups: sci.space In article <1992Nov5.015547.12219@u.washington.edu> bilgeoid@milton.u.washington.edu (Patricia Gellert) writes: > >Do any readers know if the shuttle astronauts voted by absentee ballot? > >I hope this is not considered non-topical for this newsgroup. Steve Maclean (probably misspelled) was actually in orbit when Canada held its recent "referendum" on constitutional matters. If the Canadian Space Agency was on its toes then he must have cast an absentee ballot. Not to have done so would have been politically incorrect. Canada had approximately three quarters of its registered voters turn out to vote in that election. How'd the US do in theirs? Leigh ------------------------------ Date: 5 Nov 92 20:00:55 GMT From: Larry Klaes Subject: Electronic Journal of the ASA (EJASA) - November 1992 Newsgroups: sci.astro,sci.space,sci.misc THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC Volume 4, Number 4 - November 1992 ########################### TABLE OF CONTENTS ########################### * ASA Membership and Article Submission Information * Tales of the Double Stars - Don Barry * Coping with Dew - Charlie Manahan * What Does a Computer Aided Telescope (CAT) Do? - Bob Weaver ########################### 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) 564-9623, 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. Back issues of the EJASA are also available from anonymous FTP at chara.gsu.edu (131.96.5.29) DISCLAIMER - Submissions are welcome for consideration. Articles submitted, unless otherwise stated, become the property of the Astronomical Society of the Atlantic, Incorporated. 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, Incorporated. TALES OF THE DOUBLE STARS by Don Barry In the Second Century A.D., Ptolemy noted that the star Nu Sagittariae appeared to keen eyesight as a close pair. Twenty centuries later, over one-half million measures of over seventy-five thousand star systems have been accumulated by observers around Earth, using telescopes from a few centimeters in size to the multi-meter behemoths atop high mountain perches. The first telescopically discovered multiple system was the Orion Trapezium, noted by Johannes Cysat of Ingolstadt in 1619. Mizar was split by Riccioli in 1650. Soon after Alpha Centauri, Alpha Crucis, Alpha Geminorum (Castor), and Alpha Virginis (Spica) were resolved by observers across Europe. Today the cataloguing and measurement of double stars are often regarded as an astronomical cliche. This is certainly not the case, with advances in technique and instrumentation making present measurements one hundredfold more useful than those of one century ago. Seventeenth Century observers had an additional compulsion to search the night sky for stellar pairs. Just as Galileo Galilei's discovery of the orbital motion of Jupiter's major moons demonstrated the existence of motion other than heliocentric, Sir Isaac Newton's published theory of Universal Gravitation predicted the existence of solar systems outside our own, subject to the same planetary motions. These early observers were extending the application of new theories to the Universe as a whole, at least as it was then known. Mitchell, Mayer, and Herschel separately argued the case for orbital motion in several systems, though the lack of accurate tools made comparison of measures over time difficult. By the first decade of the Nineteenth Century, rapidly moving wide systems such as Xi Ursae Majoris had spun sufficiently in their orbits that the proof was clear. Double stars did move and the motion followed an elliptical course, thus extending Newton's reach from the Sol system to the Milky Way galaxy. Double stars move in elliptical orbits, with both stars moving in space about the center of gravity of the system. However, when we observe double stars, we normally assume one star to be fixed and draw the motion of the other star in reference to it. This produces much simpler diagrams. Although in the orbit itself, each star occupies the focus of an ellipse in which the other star moves, we see an orbit projected against the plane of the sky: A circular orbit may appear with simple back-and-forth motion because we see the system from the edge. As a result, observed orbits do not have one star at the focus of the orbital ellipse. The distance of the focus from the position of the reference star reveals the angle with which we view the orbit. During each orbit, the two stars reach a most distant point (apastron) and a closest approach (periastron). These do not necessarily correspond to what we view as closest approach and widest separation, however, because of our vantage point, viewing the orbit from a side angle. For highly elliptical systems, a pair may seem immobile for decades or centuries, only to begin rapidly moving as the system moves together for a quick gravitational fling. In many cases, after a rapid periastron passage, two stars may appear in roughly the same orientation and separation as before, only the stars are now reversed. Since it is often difficult to tell one star apart from another, some periastron passages may go unnoticed. There are many double stars and only a few observers. It is a vast sky and there is always room for more measurement. The Great Star Catalogues Herschel began the race for stellar discovery and measurement. His all-sky survey in search of nebulae also revealed over seven hundred double stars, which he crudely measured without clock drive or instrumentation. F. G. W. Struve conducted the first systematic program with the 22.5-centimeter (nine-inch) Fraunhofer refractor at the Dorpat Observatory, now in Estonia. This telescope was the first "modern" research instrument. It was outfitted with a clock drive to track the sky, precision optics and eyepieces, and for double star measurement an instrument to permit far more accurate measurement than the pure guesswork of earlier surveys. The double star instrument was fitted with a bifilar micrometer, which superimposed a set of crosshairs on the visual field. The observer could merely line up the crosshairs on a double star - easier said than done for a very close pair - and read the results from an indicator dial. Using this system, Struve discovered 3,134 pairs. Otto Struve, his son, continued this work throughout much of the Nineteenth Century. The great grandson Struve continued the line, although no longer in double star work, well into the Twentieth Century. Sherburne Wesley Burnham was the premier United States contributor of the Nineteenth Century, discovering 1,336 doubles, many with the 65-centimeter (26-inch) and one hundred-centimeter (forty-inch) refractors near Chicago, Illinois. His book, A GENERAL CATALOGUE OF DOUBLE STARS WITHIN 120 DEGREES OF THE NORTH POLE, contained notes and measures for 13,665 stars. Aitken continued Burnham's work. In 1932 he published THE NEW GENERAL CATALOGUE OF DOUBLE STARS WITHIN 120 DEGREES OF THE NORTH POLE with 17,180 measurements. Jeffers, van den Bos, and Greeby continued the effort, and in 1961 issued perhaps the last catalogue of double stars to be issued in bound and printed form. Their INDEX CATALOGUE OF VISUAL DOUBLE STARS 1961.0 contained identification and the oldest and most recent measures of 64,247 double stars. Today, Charles Worley of the U. S. Naval Observatory (U.S.N.O.) maintains the world database of double star measures, the WASHINGTON DOUBLE STAR CATALOGUE, which exists as a computer file constantly being updated. It currently contains over one-half million measures of about 75,000 systems. Orbits Of these seventy-five thousand systems known to be visibly double, orbits have been computed for only about 850. The reason is that less than two centuries of accurate measurements are available. Most systems with measurements of several arcseconds, representing stars separated by many tens or hundreds of times the distance between Earth and the Sun, will take many thousands of years to complete one revolution. Accurate orbits, often called "Grade 1", only exist for about eighty systems. Methods of Detection Only a minority of double stars appear as such through a telescope. Earth's atmosphere limits easy resolution to stars with separations of one arcsecond or more, though experienced visual observers can resolve companions to 0.3 arcsecond. For very close separations, only stars of nearly equal brightness are resolvable. At greater separations, very large differences in brightness may be detected. The net effect is that relatively few true doubles appear as "visual doubles". The advent of stellar spectroscopy revolutionized binary research, providing a complementary technique capable of resolving the closest binaries, including those actually in contact with one another. Since very close stars orbit much more rapidly than widely spaced pairs do, the Doppler motion of these rapidly spinning twins shows up much more clearly in the stellar spectrum. These pairs are dubbed "spectroscopic binaries". Still other very close pairs have orbits in which one star obscures the other during part of their orbit as seen from Earth. Hundreds of these "eclipsing binaries" are known. It is estimated that about one star out of one thousand falls in this class. The brightest are Beta Persei (Algol) and Gamma Persei. Some stars reveal their double nature not through their visual appearance or their motions in the spectrum but by the composite nature of the spectrum itself. They show features common to hot and cool stars, which is possible only from a dual source. These stars are called "spectrum binaries". A few other stars, lying near the ecliptic, are resolvable during lunar occultations during which their light is extinguished in stages. About nine percent of the sky lies within the reach of Earth's Moon during its 18.6 year precessional cycle, limiting the usefulness of this technique. The statistics from these techniques yield an astonishing conclusion: Over half the stars in the sky are double! Well over ten percent seem to be triple systems. We also know of systems containing up to six stars, such as Castor (Alpha Geminorum). New Techniques One exciting new technique, speckle interferometry, has extended the useful resolution limit of "visual double stars" from one-half arcsecond to a few hundredths of an arcsecond, a factor of twenty- five improvement. In addition, this technique yields measurements of double star positions which are about one hundred times as precise (the errors in the measurements themselves are much smaller) as with a micrometer. Speckle interferometry works by taking rapid photographs of a double star, usually using a video camera, and thereby freezing the boiling motion which the atmosphere imparts to an image before it can blur the view beyond repair. Mathematical techniques, programmed on fast computers, then sift thousands of such images and reconstruct the double star within. The technique lets a quality telescope be used at its true resolution limit, set only by the size of its mirror and the wavelength of light used, rather than limited by the atmosphere to a resolution equal to that of a small amateur instrument. Sixteen years of work with this technique has resulted in the discovery of over three hundred new binary stars. All of these systems are very close, therefore having potential orbits which are much shorter than the very wide pairs which make up the bulk of known double stars. Several dozen new orbits have resulted from this work. Many of these systems are rapid enough "movers" that their motions show up in their spectra as well. These "double visual/spectroscopic" binaries are the most exciting stars of all. Although only a few percent of all double stars fit the niche - they must be close enough to move sufficiently fast for the spectrum to change and wide enough to be resolvable - the combination of spectroscopic and visual information yields a very rich harvest of information. The velocities of the stars and the period of the orbit gives the size of the orbit in space. The visual orbit gives us the apparent size of the orbit as viewed from Earth. The combination of the two of true size and apparent size gives the distance to the double star. Of all methods of determining distance, this is one of the most precise, and errors of only a few percent are possible. Once we know the distance, it is easy to calculate the mass of the stars and the total amount of energy that they produce. Imagine, the orbit of a stellar-pair lets us place them on an imaginary balance and actually weigh them! Modern Observers Only a few observers today use the old-fashioned technique of filar micrometry. The last of the breed, as it were, are Charles Worley of the U.S.N.O., Wulff Heintz of Swarthmore College, and Paul Couteau of the Universite de la Cote d'Azur in France. Worley converted to the speckle technique, using a clone of the Georgia State University (GSU) speckle system, just two years ago. Using an Alvan Clark 65-centimeter (26-inch) instrument, Worley is doing modern astronomy on a telescope 130 years old. The Smithsonian Institution already wants his micrometer! Worley is not quite done with it, he reports. Our own team at GSU has now accumulated over fifteen thousand measures with the speckle technique over sixteen years. Other groups at Harvard, Caltech, University of Wyoming, University of Hawaii, and teams in France, Australia, Germany, and the former Soviet Union have also made speckle measurements. Still, over eighty percent of the existing measures are by GSU astronomers, primarily using the four- meter telescopes at Kitt Peak and Cerro Tololo, Chile. Some Famous Doubles Some famous doubles have a few extra companions thrown in, many just recently discovered by the Center for High Angular Resolution Astronomy (CHARA) astronomers. In 1989, we discovered a fifth star in the famous double-double system, Epsilon Lyrae. This companion is in the fainter of the two pairs, although it is not yet known to which of the two stars it belongs. The separation is a tiny 0.044 arcseconds, at position angle 29.4 degrees. Try seeing that in a typical backyard telescope! Charles Worley bitterly complained when he catalogued our measurement, "You ruined my favorite star!" What do we call it now, the double-triple? Other discoveries are a companion to the golden component of Albireo, found 0.406 arcseconds away at position angle 159.0 degrees. A large brightness difference should make this component almost impossible visually, though the separation is not too terribly close. An astrophysically important double discovery is Pleione, the star at the tip of the handle in the Pleiades (Seven Sisters) dipper pattern in the constellation of Taurus the Bull. This very hot star is a favorite of GSU astronomer Doug Gies. His many spectra of the star's light reveal pulsations on the stellar surface and the presence of orbiting gas just above. In 1987, we found a companion, just 0.217 arcseconds away at position angle 54.9 degrees. Doug has subsequently found evidence for the companion in a lunar occultation which he observed at the University of Texas a few years earlier. Every thirty years, Pleione seems to acquire a fresh envelope of gas: Is the companion part of the explanation? We do not know yet, but there is exciting work to be done here. The star Capella (Alpha Aurigae), the fifth brightest star in Earth's night sky, is a signature star for the CHARA group. First split by an optical interferometer using two separate telescopes in 1921, over fifty years went by before speckle interferometry was used to resolve Capella again in the 1970s. Capella has now revolved about two hundred times since its first observation, making its orbital period the most accurately determined of all visual binaries. With a three-month period and maximum separation of only six hundredths of one arcsecond, this star requires at least a two-meter (eighty-inch) telescope for any hope at resolution. Two interesting stars have been found in orbits which are viewed nearly edge-on from Earth. From this angle, it is possible that one star will pass in front of the other during the orbit, causing the system to temporarily dim as the light of one star is shadowed. One of these systems, Alpha Comae Berenices (Diadem), might have eclipsed in early 1990. Despite a call for observers, no one reported anything unusual. We will have to wait thirty years to check again. The second system, Gamma Persei, was predicted by our group to be a favorable candidate for eclipse in late 1991. Last-minute spectroscopic observations by British astronomer Roger Griffin narrowed the possible time of eclipse to a period of a few weeks. This eclipse was actually observed, lasting almost ten days, in September of 1991. It will be twenty-eight years before another eclipse will be visible from Earth. Castor (Alpha Geminorum) consists of six stars, but only two are visible through a small telescope. Each of the two resolvable stars is a spectroscopic binary itself. The entire system is orbited by yet another very dim close double at extreme distance. During the last thirty years, Castor has rapidly moved through its orbit. With a period estimated at nearly five hundred years, Castor swung through closest approach in the middle 1970s with amazing rapidity. Coming to about 1.8 arcseconds at closest approach, Castor is already wider than three arcseconds. During thirty years, the two components have moved by more than ninety degrees, although the exciting period is now over. During the next decade, Castor will widen by almost one additional arcsecond, although the position angle will change by less than fifteen degrees. A soon-to-be-famous double was just measured by CHARA astronomer Brian Mason from 1988 data taken with the CFHT telescope on Mauna Kea in Hawaii. It is a white-dwarf binary, shining at a faint magnitude 12.3 in the handle of the Big Dipper. This object is well within the reach of amateur telescopes, with a separation of 2.6 arcseconds in position angle 125. Let us know if you can confirm it! The coordinates are RA 12h 50m 05s, +55d06.0m declination (2000). The Difficult Ones The brightest star in the sky, Sirius, had its own surprises for the latter Nineteenth Century. Observations of the slow proper motion of Sirius throughout the early part of that century showed that Sirius does not quite move in a straight line through space. The luminous star is tugged from side to side by an unseen companion. Many observers tested their instruments in vain to find the culprit. Success came with a new refractor, the 65-centimeter (26-inch) Dearborn telescope, funded by the Chicago Astronomical Society during the late 1860s. During the telescope's first checkout, the companion to Sirius was plainly visible, about ten arcseconds away. Fortunately, the observers peeked at the right time: Sirius' companion was near its most distant position. At present, the Chicago Astronomical Society's logo contains the orbit of Sirius B in its design. Sirius' friend is an 8.5 magnitude white dwarf star, the ember of a companion once mightier than Sirius itself. With a fifty-year orbital period, this star moves from 2.5 to ten arcseconds away from Sirius. With almost ten magnitudes difference in brightness (ten thousand times difference!) the companion is visually undetectable in even the largest instruments near closest approach. Sirius B most recently reached widest separation in 1971. It has been moving towards closest approach, to occur in early 1993. It will probably not become easily visible in even the finest telescopes until the year 2000, when it will approach five arcseconds separation. However, former GSU astronomer Wean-Shun Tsay, using a 35-centimeter (fourteen-inch) Celestron atop the observing mountain of Taiwan's National Central University, last year resolved Sirius B with a CCD video camera, averaging many frames together to get a clear image. This year, Sirius B moves from position angle 330 to 300, presenting one of the ultimate challenges to small instruments and acute vision. An even tougher challenge is presented by Procyon, another bright star with an even fainter white dwarf companion. Procyon's secondary is magnitude 10.3 and never farther than 5.2 arcseconds distance. Orbiting every forty years, it achieved widest separation just last year, although no measurements have been made in decades. Perhaps no one has bothered to look. Charles Worley claims that he is perhaps the last person to have viewed the companion and perhaps one of the few people alive to have ever seen it. Procyon B is currently at position angle 30 and not moving very fast. It should maintain its current separation for the remainder of the decade, sliding in towards the next close approach in the year 2009. Related EJASA Articles - "The CHARA Multi-Telescope Telescope", by Hal McAlister - August 1989 "A View from Taiwan: Wean-Shun Tsay", an interview by Edmund G. Dombrowski - August 1989 "Our Closest Neighbors in the Milky Way Subdivision", by Ingemar Furenlid and Tom Meylan - September 1989 "Long-Term Trends in Ground-Based Astronomy", an interview with Dr. Hal McAlister by Edmund G. Dombrowski - January 1990 "Stellar Spectroscopy: At the Heart of Astrophysics", an interview with Dr. Ingemar Furenlid by Edmund G. Dombrowski - March 1990 "Sir William Herschel and the Natural History of the Heavens", by Keith M. Parsons - June 1991 "The Hyades: A Star Cluster Rich in Myth and Astronomy", by Ken Poshedly and Don Barry - June 1992 About the Author - Don Barry, ASA President and Charter Member, is an astronomer with the Center for High Angular Resolution Astronomy (CHARA). Don is currently writing his Ph.D. thesis involving measuring the relative luminosity of very close double stars. Don's professional interests include optical interferometry, binary astrometry and photometry, and innovative instrumentation. An active amateur as well, Don's interests include telescope making, antique instruments, and fostering amateur- professional collaborations. Don is the author of the following EJASA articles: "Astronomy Week in Georgia" - August 1989 "Profiles in Astronomy: Albert Whitford" - September 1989; an interview with Edmund Dombrowski and Sethanne Howard "Alar Toomre: Galactic Spirals, Bridges, and Tails" - October 1989; an interview with Edmund Dombrowski and Sethanne Howard "Observing the Wreaths of Winter" - December 1989 "The Mayall Four-Meter Telescope" - May 1990 "A Southern Travel Diary: An Observer's Tale" - August 1990 "Saturn's Great White Spot" - February 1991 "The Hyades: A Star Cluster Rich in Myth and Astronomy" - June 1992; with Ken Poshedly COPING WITH DEW by Charlie Manahan How many amateur astronomers have been out happily observing, only to find their celestial targets slowly fade into the background? The culprit is dew, usually covering the front optical element of their telescopes. What is dew? Where does it come from? Most importantly, what can we "dew" about it? The most popular amateur telescope design is the Schmidt-Casse- grain, which is particularly susceptible to dewing on its exposed front corrector. However, any optical element exposed to the open air can (and usually will) dew, given sufficient time and a humid night. Dew does not fall from the sky. It is the same phenomenon that causes the glass holding your iced drink to get wet. Any object that is colder than the condensation point (dew point) gets moisture on it. If the object is cold enough, the condensate is ice, otherwise liquid. Why do Schmidt-Cassegrain corrector plates seem to be the first to fog? For any given set of atmospheric conditions, dew formation is a function of temperature. Schmidt-Cassegrain correctors are usually colder than other things around an observing site. Why? The temperature of different objects at an observing site can vary considerably, depending on the heat flow into and out of the objects. All things in the Universe give heat to objects that are colder and accept heat from objects that are warmer. The temperature of any object that does not generate its own heat is solely dependent on the net heat flow to and from that object. The corrector of an SC is no exception. The corrector is at a steady state temperature and heat flow achieved by radiating heat to the night sky and accepting heat from the terrestrial surroundings. Deep space is at the temperature of the microwave background, a frigid 2.73 degrees Kelvin (-454 degrees Fahrenheit). An unshielded corrector plate pointing at the zenith "sees" a hemisphere of extreme cold above it and only the telescope below it. Since the night sky is so much colder than the corrector, the corrector radiates heat to the sky. As long as the heat flow out of the corrector is greater than the heat flow into it from the air and surrounding objects, the corrector gets colder. The colder the corrector becomes, the more heat flows into it and the less heat flows out. The temperature continues to drop until the heat flow in matches the heat flow out. If the steady state temperature of the corrector is lower than the dew point, the corrector gets covered with dew. Wiping it will not help; it will only redistribute the dew. The one act that will prevent dew formation is keeping the corrector plate temperature above the dew point. There are two ways to keep your optics warm enough to prevent dew. One is to reduce the heat flow out by reducing the area of night sky that the corrector "sees". This is how dew shields work. By narrowing the circle of sky to which the corrector is exposed, the heat loss is reduced and the steady state temperature of the corrector increases. Dew shields have an additional benefit of increasing image contrast by reducing optical flare caused by stray light. The longer and deeper the dew shield, the better it works. This is why Newtonians have less trouble with dew than Schmidt- Cassegrains. Their mirrors are only exposed to a small portion of the sky. With humid nights in such places as Georgia, dew shields are rarely sufficient to keep the dew away, although they slow dew formation. In addition, as the environment cools throughout the night, the ambient temperature can drop to or below the dew point, making dew shields useless. At this point, the only way to prevent dew is by artificially heating the corrector. Hair dryers work, but dew clearing with a hair dryer requires a 120V power supply and is a repetitive chore. On a night with heavy dew formation the corrector may require a "blow dry" every ten minutes. Corrector plate heaters are a step up from hair dryers but can cause convection currents that generate bad "seeing" through the telescope. A combination dew shield and corrector plate heater with a temperature control that allows the heater to work at a temperature just barely warm enough to keep the corrector above the dew point is a better solution than either alone. Amateurs can save money on dew shields without much effort. Commercial dew shields are expensive and usually too short. A rolled poster board tube painted with the polyester resin used for automotive fiberglass makes an acceptable dew shield. Untreated poster board sags out of shape as it gets wet with dew during the night. Painted aluminum flashing (easily joined with pop rivets) makes an inexpensive, durable dew shield. For those who like to solder, resistors for heating are cheap. As a starting value for twenty-centimeter (eight-inch) SCTs, twelve three ohm resistors in series (36 ohms total) should give plenty of heat to keep dew away when attached to an automotive battery (13.6V). This gives about four-tenths of one watt per resistor. Allow a safety margin of 5x on the power factor for resistors. Just be sure to mount them close to the corrector and give your construction the "smoke test" before you put it on your telescope. Do NOT plug this into a household outlet - it may cause an electrical fire! The ideal solution maintains the optical element temperature slightly above the dew point, while minimizing temperature differences and air currents in the optical path. Related EJASA Articles - "Amateur Telescopes, Yesterday and Today", by Bill Bagnuolo - September 1989 "A Comparison of Optical and Radio Astronomy", by David J. Babulski - June 1990 "Low-Budget Astronomy", by Tony Murray - October 1990 "Aperture Arrogance", by Eric Greene - March 1991 "Astronomy and the Family", by Larry Klaes - May 1991 "An Introduction to Celestial Coordinates", by Nils Turner - October 1991 "Astrophotography the Easy Way", by Harry Taylor - October 1991 "How to Make a High-Quality Fifty-Millimeter Finderscope", by Robert Bunge - December 1991 "The Elusive Dot", by John Stauter - December 1991 "Telescopes: A Novice's Guide", by Steven M. Willows - March 1992 About the Author - Charlie Manahan is a familiar ASA member to fellow observers at Hard Labor Creek Observatory (HLCO) activities. Charlie pursues astrophotography and deep sky observing through his custom modified Celestron 11 telescope. His hardware attests to the value of a little "do it yourself" magic, which always seems to make things work better. WHAT DOES A COMPUTER AIDED TELESCOPE (CAT) DO? by Bob Weaver (From the ASA BBS) Here is a summary of what a Computer Aided Telescope (CAT) accessory can and cannot do for you. Misconceptions Contrary to popular belief, a CAT will not polar align your telescope. It can greatly simplify the process if you follow a relatively difficult "first time" start up procedure. Personally, I found it simpler to polar align at each observing session. The procedure takes about ten minutes. If you are having trouble with polar alignment and cannot locate celestial objects with setting circles, the CAT will not be able to, either. You must have very precise polar alignment. I highly recommend the polar axis finder by Rodger Tuthill. It aligns the mount, not just the telescope tube assembly! What Can a CAT Do? 1. Keeps track of the sky coordinates (RA and Dec) that your telescope is pointed at. 2. Keeps track of the coordinates and characteristics of thousands of astronomical objects. The CAT serves the same function as hardcopy star charts plus reference books, but in a much more convenient form. 3. Keeps track of miscellaneous information that is necessary or useful during observing, like time, date, site location, etc. (This is optional.) 4. Identifies the object closest to the center of the field and tells how many other NGCs are in the same field. (This is optional.) 5. Automatically selects objects to view based upon characteristics that you specify (type, brightness, size, visual quality, minimum altitude) in a sequence that minimizes the distance between objects. A display may describe them and an indicator may lead you to them, one after another. (This is optional.) Popular Data Bases * The NGC database of 8,163 objects. * Bright stars (as many as 351) for polar/coordinate setup. * Double and multiple stars. * Messier objects M1 through M110. * Planets in their current locations. * Bright planetoids. Common Features * LED display of telescope RA/DEC * Display of object description, catalogue number * Command keys with audible, visual, and tactile feedback for entering commands and information to a CAT. * Bar LEDs to indicate direction and distance to an object of interest. * Star map with different resolution views of a region and finder chart of object. (For sophisticated models.) * Most consume less than ten watts of power. * Most offer encoder resolution of at least 1/8 degree in RA and 1/20 degree in Dec. Installation Most CAT brands require installation of two encoders on the axes of the telescope. They often contain special brackets for mounting to popular brands. Cables run from the encoders to the CAT control box. If you are not mechanically inclined, do yourself a favor and ask for help from a dealer or a knowledgeable ASA member. If you break an encoder, it will cost from 125 to 200 dollars to replace it. Operation When searching for a particular object, I use a 32-millimeter (mm) eyepiece, which delivers a 0.86 degree field with my telescope. If the telescope is polar aligned properly, the object will always be somewhere in the field of view. No other accessory has enhanced my enjoyment of astronomy more that the CAT. I find myself spending time observing rather than searching. Also, since I do not need to fumble through star charts and manuals looking for object coordinates, I take more chances looking for extremely faint objects. This overview was based on the Meade CAT. There are a variety of CATs to chose from. Some have more features than the Meade and others have less. If you have any questions about my system, please contact Bob Weaver with a message on the ASA BBS. THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC November 1992 - Vol. 4, No. 4 Copyright (c) 1992 - ASA ------------------------------ Date: 5 Nov 92 13:07:32 CST From: Dudley Knappe Subject: Thanks for the help! Newsgroups: bionet.plants,sci.bio,sci.bio.technology,sci.research,sci.space I want to thank all who responded to my call for references on geo/gravitropism. Specifically: Thomas Bjorkman, Cornell University George Ellmore, Tufts University Ray R. Hinchman, Argonne National Laboratory (Most of the list, thanks Ray) Gerard R. Lazo, The S.R. Noble Foundation, Inc. Randall Legeai, Tulane University William E. Williams, St. Mary's College of Maryland Richard Winder, Pacific Forestry Centre, Victoria, B.C. Allen (adwright@iastate.edu) With your help I have gotten many references that will occupy quite a bit of time reading, Thanks!!!! If anyone is interested in a copy of the reference list I have (total of 51 references), please send me some e-mail at dudley@fig.cray.com and I will be happy to get it to you by return e-mail. Again, thanks. -- Dudley Knappe, Software Development Division Cray Research, Inc. Phone: (612) 683-5529 655F Lone Oak Drive E-mail: dudley@cray.com or uunet!cray!dudley Eagan, MN 55121 ------------------------------ Date: 5 Nov 92 20:45:45 GMT From: Sam Warden Subject: the Happyface on Mars Newsgroups: sci.space Lawrence Curcio writes: >According to _Flying Saucers - Serious Business_, by Frank Edwards, a >face was detected in a visual representation of radio signals from Mars. >The signals were recorded by C. F. Jenkins in 1924. Then, years later, >we get the face from a space probe. So much for that authoritative work. Jenkins was sounding the newly-discovered ionosphere I believe, and got some anomalously long-delayed echoes. Nuch later someone fitted the frequency- delay plot to a map of some nearby stars, but I don't think there was ever a connection with Mars. I don't know that his equipment was directional enough, or the frequencies high enough, to have done so anyway. Odds are it was the magnetosphere. ;-) -- samw@bucket.rain.com (Sam Warden) -- and not a mere Device. ------------------------------ End of Space Digest Volume 15 : Issue 385 ------------------------------