National Capital Astronomers, Inc. Phone: 301/320-3621

Volume 55, Number 4 December, 1996 ISSN 0898-7548

Cosmic Rays and Super Nova Remnantsby Andrew W. Seacord, II

The 1996 December meeting of theNational Capital Astronomers will beheld Saturday December 7 at 7 :30 at theLipsett Amphitheater in the ClinicalCenter (Building 10) of the NationalInstitutes of Health (NIH). Our speakerwill be Robert Petre of the GoddardSpace Flight Center Laboratory forHigh Energy Astrophysics. His re-search areas involve x-ray astronomyand cosmic rays in super nova rem-nants.

Super nova remnants (SNRs) areone of the products from the cataclysmicdeaths of stars having a main sequencemass greater than about 8 solar masses.Observations of SNRs throughout theelectromagnetic spectrum show thespectra of synchrotron radiation whichis produced by the encounter of elec-trons, traveling near the speed of light,with a magnetic field. From this weinfer that SNRs contain high particleenergies and a magnetic field which, inplaces, is substantially greater than theaverage magnetic field of the galaxywhich is in the order of a fewmicrogauss. (The magnetic field of theearth near the surface is about 0.5gauss.) Another indication of high ener-gies in SNRs is the fact that our favoriteSNR, the Crab Nebula, is a strong x-raysource. These high energies have beensustained for so long by the pulsar at thecenter of the Crab.

Cosmic rays are high energy par-ticles - not electromagnetic radiation

sonable to suspect that the large mag-netic fields present at the time of thesupernova explosion are very capable ofaccelerating the heavy element nuclei,ejected by the explosion, to high ener-gies and, thereby, creating the non-solarcosmic rays. The presence of the Milky

- which have two components. Onecomponent is a stream of protons pro-duced by solar activity, mainly solarflares. The other component of cosmicrays comes to us from all directions.They are distributed evenly around thecelestial sphere and consist mainly ofprotons but also nuclei of heavy ele-ments from helium to those with anatomic number greater than 10. Thesource of these cosmic rays is not cer-tain. However, it is known that theproduct of stellar death is the nucleosyn-thesis of heavy elements. It is not unrea-

Way's magnetic field will scatter theseparticles so that we observe them tocome from all directions around the ce-lestial sphere. There is more to say, butthat is the subject of Dr. Petre's talk forthe NCA December meeting. 0

Super Nova Remnant NGC 6543a, Hubble Space Telescope» Wide FieldPlanetary Camera 2 (WFPC2), January 1995

Calendar of Monthly Events

The Public is Welcome!NCA Home Page: http://myhouse.comiNCAlhome.htm

Mondays, December 2,9,16,23 and 30, 7:30 PM-Public nights at U.S. Naval Observatory (USNO), inNorthwest Washington, D.C. (off Massachusetts Av-enue). Includes orientation on USNO's mission,viewing of operating atomic clocks, and glimpsesthrough the finest optical telescopes in the Washing-ton-Baltimore region. Held regardless of cloud cover.Information: USNO Public Affairs Office, 2021762-1438. Home page: http://www.usno.navy.mil.

Tuesdays, December 3,10, and 17,7:30 PM-Tele-scope making classes at Chevy Chase CommunityCenter, Connecticut Avenue and McKinley Street,NW. Information: Jerry Schnall, 202/362-8872.

Fridays, December 6, 13, and 20, 7:30 PM-Tele-scope making classes at American University,McKinley Hall Basement. Information: Jerry Schnall,202/362-8872.

Fridays, December 6,13,20, and 27, 8:30PM -Opennights with NCA' s Celestron-14 telescope atRidgeview Observatory; near Alexandria, Virginia;6007 Ridgeview Drive (off Franconia Road betweenTelegraph Road and Rose Hill Drive). Information:Bob Bolster, 703/960-9126.

Saturday, December 7, 5:30 PM-Dinner with thespeaker and other NCA members at North ChinaRestaurant at 7814 Old Georgetown Road (nearCordell), Bethesda, MD. See map and description onback page.

Saturday, December 7,7:30 PM-NCA meeting, willfeature Robert Petre (Goddard Space Flight CenterLaboratory). His talk will be "Cosmic Rays and SuperNova Remnants." More information on Comet Hale-Bopp will also be provided. For directions, see mapand description on back page.

Wednesday, December 11, Noon to 1:00 PM-Lec-ture: Tom Crouch, Curator, and Dominick A. Pisano,Curator, Aeronautics Department, National Air andSpace Museum (NASM), "A Poised for Take-Off:The Roots of the National Air and Space Museum,

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1876-1976," in celebration of the 50th anniversary ofNASM and the 20th anniversary of the NASM building.Located in the Mayer Auditorium of the Freer Gallery ofArt; free to the public. For more events and details seepage 8.

Wednesday, December 11, 11:00AM-Lecture: BruceCampbell, NASM, "The Mountaintops of Venus," De-partment of Terrestrial Magnetism, Carnegie Institute ofWashington, 5241 Broad Branch Road, NW, Washing-ton, DC. Information of weekly events: (202) 686-4370(exts. 4378 or 4383).

Sunday, December 15, 7:00 PM-Wintertime Stars,Historic Bladensburg Waterfront Visitor Center, 4601Annapolis Rd., Bladensburg, MD. Details &Directions: Geoffery C. Lane (NCA), 301/927-2163, or301/927-8166 (fax).

Saturday, December 21, 7:00 PM-"The Day of theSun's Return, the Winter Solstice." MontogomeryCollege's Planetarium, Takoma Park, MD. Informa-tion: 301/650-1463.

NCA and National Park Service (NPS) Exploring theSky program will be continued in the spring. Details &Directions: Nature Center, 202/426-6829; Joe Morris(NCA), 703/620-0996. Nature Center Home page:http://www.nps.gov/rocr/.

See page 8 for more Washington area astronomicalevents. Other events too numerous to list in Star Dust arelisted in the publications Sky & Telescope, the Astro-nomical Calendar 1996, the Observer's Handbook1996, in numerous software packages, and other linksavailable on the NCA Home Page (see above for ad-dress). NCA members can purchase all these (and muchmore) at a discount. To join NCA, use membershipapplication on page 9.

During questionable weather, call the IOTA Hotline(Phone: 301/474-4945) for NCA meeting status. Theabsence of a cancellation notice on the Hotline means themeeting will take place.

Radio Galaxies Summary and Review

by Gary L. Joaquin

At our November meeting, Dr. JohnGraham gave a presentation on radiogalaxies. He was quick to state that hewas an astronomer, but not a specialistin radio galaxies, although it has been atopic of great personal interest to him formany years. The presentation that fol-lowed was informative, engaging, andeven entertaining. The question andanswer session that ensued immediatelyafterward was one of the most animatedthat I have seen in my four years as anNCA member. In writing this review, Iam hopeful to not only capture the con-tent of his lecture, but to relate some ofthe enthusiasm and wonder that was feltat this meeting.

One hundred years ago we wereknowledgeable about the solar system.We knew about stars. We didn't knowvery much about galaxies. We weren'tcertain if galaxies were within our ownMilky Way galaxy or separate star sys-tems in their own right. More recentlywe have discovered objects like pulsars,quasars, and black holes. The universeis indeed more complicated that we hadever imagined.

Up untilSf years ago our knowl-edge was obtained exclusively from ob-servations made in visual wavelengths

visible to our own eyes. In the last SOyears we've been able to view the uni-verse in a much wider range of wave-lengths from a variety of new vantagepoints. Short wave lengths like gammarays and x-rays are blocked by our atmo-sphere, requiring observation fromspace. Infrared observations can bemade at high altitudes above the watervapor interference of our atmosphere.Longer wave lengths like radio wavespenetrate our atmosphere enough to beobserved from the ground.

The National Radio AstronomyObservatory has published pictures ofthe sky as it would appear at a wave-length of 6 centimeters. At first glancethese images look like the same starsthat we see in the visual wavelengths,yetstars are comparatively weak as radiowave radiators. They are also relativelyclose, averaging in distance of about100 light years. In reality, the points oflight that appear in the radio sky areradio galaxies that are typically 400 toSOO million light years away; very un-usual objects to be so distant and soluminescent. By changing the wave-length in which you are viewing anotheruniverse appears to pop out.

When radio astronomy began in the1940s the first discrete radio sources tobe discovered were radio galaxies withnames like Virgo A and Centaurus Awhere "A" denotes the brightest radiosources in a given constellation. Theseradio galaxies often turned out to beunusually bright objects in the visualspectrum and received our attentionfirst. While it is true that all galaxiesradiate radio waves, not all galaxies ra-diate strongly. Our Milky Way is atypically weak source of radio wavesradiating at a rate of about 1037 ergs/sec.(Our Sun radiates in the optical range atabout 1033 ergs/sec) Typical radio gal-axies are much stronger, ranging from 1million to 100 million times more radi-ant.

Centaurus A (see figures 1 and 2) isthe nearest of the radio galaxies and haslong been recognized as a truly unusualobject. When it was first discovered byradio astronomers in Sydney, Australiaone of the biggest surprises was howlarge it was; the radio source itself ex-tends about S or 6 degrees across the sky,about a tenth of a radian. We have sincedetermined that this galaxy is about 10million light years away, making thisradio source about 1 million light yearsacross, 10 times wider than our ownMilky Way galaxy. These objects areprobably the largest integral objects thatwe know about, only surpassed by clus-ters of galaxies and other fine structuresin the universe. Some of the moredistant radio galaxies are known to be upto S to 10 million light years across.Closer examination of this galaxy re-vealed a structure consisting of largeradio lobes jetting out from a very com-pact nucleus.

Radio galaxies like Centaurus Awere discovered at a time when the firstatomic particle accelerators were beingconstructed in the 1940s and 19S0s.During this time it was determined thatthe radio emission from these galaxieswere very similar to that produced bysynchrotron accelerators. One sees in aradio galaxy very similar radiation withelectrons moving close to the speed oflight. The total amount of energy stored

See GALAXIES, continued on page 4Figure 1) Centaurus A (also known as NGC 5128), a nearby galaxy in thesouthern sky, exhibits huge radio lobes stretching several degrees across the sky.

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GALAXIES, continued from page 3

in these objects is on the order of 1057 to1061 ergs. Energies of this magnitudecannot be sustained for long unless re-plenished constantly. Radio galaxiesimmediately raise the questions: Howare they continually powered? Will theylast forever? How can we use them toprobe the depths of the universe as farout as we can detect such galaxies?

Lets look at another example. Theradio galaxy Cygnus A was mappedwith the Very Large Array in NewMexico. This galaxy is much moredistant that Centaurus A, about 600 mil-lion light years away. Like CentaurusA, Cygnus A was detected during theinfancy of radio astronomy. Optically,if you look in the direction of Cygnus Aall you see is a dim 17th magnitudegalaxy in the center. Through a verylarge telescope it looks very much likeCentaurus A, an elliptical galaxy with agas lane across it. Its radio lobes aresomewhat smaller than Centaurus A's,extending out approximately half a mil-lion light years. Very narrow jets can beseen coming from the galaxy's center.

The structures that we have exam-ined in both of these examples requireremarkable dynamics to sustain them.Collimated jets originating from a cen-tral source, create large lobes visible inthe radio wave lengths on either side ofthe galaxy. These lobes do not rotate; itwould require impossibly largeamounts of angular momentum to tumthem. They are essentially two big bal-loons blowing out on either side of thegalaxy. Measuring the speed of thesejets so far has been impossible withoutobservation of spectral lines. However,we can estimate how fast this material ismoving. In order to get out this far, onthe order of hundreds to several millionsof light years, the limiting factors be-comes the age of the Universe and thespeed of light. Given a Universe that is10 to 20 billion years old, there is notenough time for this material to movethese great distances at velocities be-tween 10 and 100 km/sec (1 km/sec '"1.6 miles/sec). We think that this mate-rial is moving somewhere between 1000and 10,000 km/sec. However, thehigher the velocity, the more difficult itbecomes to describe this mechanism.We believe that there almost certainlyneeds to be something like a black hole

Figure 2) Centaurus A (also known as NGC 5128)

in the center of this structure. One of thegreat things that has occurred recently isthat we have come to believe that blackholes really do exist. The dust lanesaround galaxies like Centaurus A so farpreclude any measurements to provethis. Virgo A (Messier 87) is a betterexample. Astronomers using theHubble Space Telescope have measuredspectra of gasses moving so rapidlyabout the core of that galaxy that it isalmost certain to contain a black hole.

We believe that almost all of theradio galaxies have a black hole with amass of 100 million times greater thanthat of our sun existing in a volumeroughly equal to our solar system. Theseobjects are often called "super blackholes" because they are so much largerthan the black holes postulated to be atthe center of x-ray sources. These "su-per black holes" have very peculiarproperties. Because they are so large,they are not very dense. The averagedensity of these black holes is notthought to be more than I gram/em', thedensity of water. While this is not verydense when compared to ordinary mat-ter, compared to interstellar space it isvery dense indeed. When anything fallsinto these objects, they can't get out.They are true black holes.

Now that we understand some ofthe components lets examine how theyinteract in a model. Figure 3 shows thetypical structure of a radio galaxy. Hereyou can see the a nucleus, probably ablack hole, in the center of an accretiondisk of dust and gas, that are all spinning

very rapidly. As this material is pulledtowards the black hole, its angular mo-mentum is conserved, and it begins torevolve about the black hole faster andfaster. Some of the material passesthrough the event horizon and into theblack hole. The rest of the materialcontinues to revolve faster and fasteraround the black hole. Some of theatoms lose electrons and become ion-ized, thus generating magnetic fields.Density and pressure build up forming afunnel shaped cavity around the blackhole. To relieve this pressure high ve-locity jets form in the paths of leastresistance perpendicular to the rapidlyrotating disk, moving at velocities be-tween 1000 to 10,000 km/sec. Thedense dust and matter helps to focus thebeams. As we described earlier, theparticles have a synchrotron radiationsignature. These jets shoot out greatdistances on the order of a million lightyears on each side. As the jets interactwith the less dense intergalactic me-dium they eventually begin to disperse.The outer shells drawn denote the area inwhich this effect is felt. Most of theenergy is due ultimately to gravity, theweakest of the physical forces (the oth-ers being electromagnetism, and thestrong and weak nuclear forces). Mate-rial jets out and more material falls backinto the rapidly rotating disk to perpetu-ate the process. When the density of thismaterial drops below the level requiredto sustain the jets, they just go out leav-ing large radio lobes behind.

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Figure 3) Schematic diagram showing the structure and mechanism of strongdouble radio sources. Most of the radio emission is producted in the "hot spots"and lobes, by jet material that has splattered against the interstellar orintergalactic medium. (From Scientific American Library's Gravity's FatalAttraction.

We don't understand the precisemechanism but are beginning to get ageneral idea. A spinning black holebehaves like a spinning conductor. Ifthe hole is surrounded by ionized, con-ducting gas carrying a magnetic field,then a voltage difference is set up be-tween the poles and the equator, and thehole can act like a battery (see figure 4).The electric current driving the voltagedrop can extract energy from the spin ofthe hole, which can be transformed intooutflowingjets. It's worth pointing outthat when one finds these electrons spi-raling within a magnetic field producingsynchrotron radiation, particles can wellbe moving close to the velocity of light.There might not be very much motion inthe direction of the magnetic field, butit's quite possible to have very highvelocities in the direction of the spiral.

It must be emphasized that few con-clusions about radio galaxies can bemade unless we can see in visual wave-lengths the very faint galaxy in themiddle of all these structures. All of ourmethods for measuring distance arebased upon observations that are madein the very narrow spectrum of visiblelight. Without data compiled from vi-sual wavelengths we can't measure dis-tances, sizes, or the amount of energyinvolved. On the other hand if you candetect a faint galaxy in the middle ofthese structures you can measure out the

red shift and if you know the Hubbleconstant for the expansion rate of theuniverse within a factor of 2, then youcan begin to measure these quantitiesand begin to get a feeling for what isgoing on. This is why most of the workin radio galaxies in the 1960s focused onidentifying these discrete galacticsources, to find a source in a visiblewavelength that corresponds to a radiosource. In fact, work being done todayis focusing more and more on visiblerather than radio wavelengths as largertelescopes and more sensitive detectorsare enabling us to study the faint galax-ies themselves.

It is interesting to note that whencounts of radio sources have been per-formed (analogous to star counts) wefind that dim radio galaxies are morenumerous than bright radio sources.Counts of progressively dimmer radiosources yield progressively higherquantities of sources. If the strength ofa radio source is any indication of dis-tance (as visual magnitudes are for stars)then these results suggest that radio gal-axies were much more common in theearlier days of our Universe than theyare today. When the Universe wasyounger and denser, the conditions re-quired to create black holes and thedynamics required to sustain a radiogalaxy were much more favorable thanthey are now.

The study of radio galaxies in in-dicative of a really basic motivation tostudy astrophysics. Given the entireUniverse as our laboratory we can studythe dynamics of systems spanning mil-lions of light years rather than the meremillionths of light seconds that we cancreate in our Earth bound linear accel-erators. We can study 100 million solarmass black holes while the presence ofeven a small black hole at one of ourobservatories would produce irreconcil-able difficulties. We can observe phe-nomena at scales that are far greater thananything that can be duplicated onEarth. Hence our wonder at the im-mense diversity in our universe and ourhumility in our ability to perceive it. 0

Figure 4) A spinning black holebehaves like a spinning conductor. Ifthe hole is surrounded by conductinggas carrying a magnetic field, then avoltage difference is set up betweenthe poles and the equator, and thehole can act like a battery. Theelectric current driven by the voltagedrop can extract energy from the spinof the hole, which can be transformedinto outflowing jets. (Credit: All fourimages come from the ScientificAmerica Library, Gravity'S FatalAttraction.)

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Mid-Atlantic Occultation Expeditions for the Rest of 1996Lunar Grazing Occultations

DATE Day EST Star Mag % alt CA Location

Dec19 Thu 23:05 110328 7.2 78+ 43 4N Marlton & Temple Hills, MD; Alexandria,V ADec22 Sun 18:28 a.Tauri 0.8 96+ 13 9S s. of Gary, IN Sun alt. -2 deg.

Asteroidal Appulses and Occultations

DATE Day EST Star Mag Asteroid dmag duro ap, Locationsec. in.

Dec07 Sat 22:36 G1853-1759 9.6 22 Kalliope 0.9 15 5 northern FloridaDeclO Tue 19:37 pi Arietis 5.2 975 Persev. 9.5 7 1 Florida, BermudaDec17 Tue 4:08 G2345-0183 9.0 704 Interamnia 1.6 30 5 Georgia, S. CarolinaDec21 Sat 6:30 G0303-0485 9.7 13 Egeria 2.2 8 6 western CubaDec26 Thu 20:42 PPM 240941 9.8 39 Laetitia 1.7 6 6 s.w. CanadaDec28 Sat 6:32 SAO 078707 8.3 972 Cohnia 5.0 6 3 Kentucky, N. Carolina

Notes:Dec. 22: The star is alpha Tauri (Aldebaran), the brightest star that can be occulted by the Moon.

Comet Hale-Bopp CountdownBy Daniel Costanzo

November ObservationsThis past November saw the incomingComet Hale-Bopp (officially desig-nated CI1995 01) faintly but definitelyvisible just after dark and within easyreach of both binoculars and the small-est of telescopes at dark-sky sites, andeven at some suburban locations. I wasable to easily view this fuzzy visitorfrom afar with binoculars on a mid-November night under a waxing, nearlyFirst Quarter Moon at NCA' s Elkwood,Virginia Field Station, a little over anhour's drive beyond the Beltway. InCelestron 8x56 binoculars, it was asmall white puff with a short, faint tailwith a length about three-quarters theangular diameter of the Moon. In aCelestron-8 telescope its center ap-peared as a quite "stellar" central point.

As of November 22, Hale-Boppwas continuing to hold its own, slowly"cooking" under increasing warmthfrom the Sun's fusion fire, and givingnothing but good omens for a brightspectacle early next year placing itwithin easy reach of unaided eyes. Inbrightness, in mid-November, the

comet was in the mid-4th magnituderange and slowly getting brighter.

December PredictionsAs December begins, Comet Hale-Bopp will be found steadily chuggingSunward, eating up almost two millionkilometers a day of its comet-to-Sundistance. But at about 2.1 times Earth'sdistance from the Sun, or2.1 astronomi-cal units (AU) -320 million kilometers- a distance corresponding to roughlythe Asteroid Belt's inner edge, Hale-Bopp still has quite a way yet to gobefore reaching "perihelion" (closestapproach to the Sun) of 0.9 AU duringprime viewing time early next April.(The AU is the common unit of SolarSystem measurement, where 1 AU isEarth's mean orbital distance from theSun, or 149,597,870 kilometers. So 0.9AU is just inside Earth's orbit, or about135 million kilometers from the Sun,and between the orbits of Earth andVenus.) By December's end, that dis-tance will decrease to about 1.8 AU.This means that come the New Year,Hale-Bopp will have finally entered

what is called the Inner Solar System, asdefined by an imaginary sphere cen-tered on the Sun and extending to theplanet Mars' farthest distance from theSun.

Besides decreasing its comet-to-Sun distance, Hale-Bopp's comet-to-Earth distance is also slowly decreasingas both objects do an interplanetary bal-let, causing the comet to continue a longslide toward "perigee" (closest ap-proach to Earth) of 1.3 AU late nextMarch. Between December's begin-ning and end, the comet's distance fromEarth will shrink from 2.9 to 2.6 AU.

December is about the last month toget any kind of view ofHale-Bopp in theevening sky before it eventually getstemporarily swallowed up in twilight'sglow come mid-December. Best view-ing nights are in Moon-free skies duringthe first week or so of December. Dur-ing this period, with the arrival of dark,the comet can be found only a few de-grees up in the southwestern sky. Afterthat, Hale-Bopp will be gone until mid-January when it reappears low in themorning twilight.

NCA ResourcesThanks to NCA, there's no reason whyyou should be kept in the dark about this

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promising comet. Instead, we can putyou in the dark watching it. If you wishmore information on Hale-Bopp, con-sult Sky & Telescope magazine, espe-cially its high quality finder charts. Inparticular, see the September issue(pages 72-73), October issue (page 67),November issue (page 71), and Decem-ber issue (page 75). (Sky & Telescope isavailable to NCA members at a dis-count.) For further information via tele-phone recordings, call Sky &Telescope's "Skyline" (617/497-4168).Via the World Wide Web, go the NCA' shome page (http://myhouse.comiNCAIhome.html). Bob Bolster (NCA) canalso give expert, practical advice onviewing, photography, and electronicimaging (Phone: 703/960-9126, e-mail:73257.507@compuserve.com). Bobcan also provide customized listings and

charts of comet positions, viewingtimes, etc.

Information and data for this articlewas obtained from Bob Bolster (NCA),and from "Skyline" for 1996 November1,8, and 22.

Telescope ShoppingOne word of warning for those in aseasonal buying mood contemplatingpurchasing a telescope for viewingComet Hale- Bopp next year: You willbe bombarded by advertisements forthis or that instrument. Ignore them!The real rule about great comets is this:If you need a telescope to see it, then itisn't a great comet. Buy a pair of qualitybinoculars instead. An aperture (mainlens diameter) of no less than 50 milli-meters is ideal (e.g., 7x50). They'remore suitable, a whole lot lighter, and

most of all cheaper than an expensivetelescope loaded down with unneces-sary gizmos and doohickeys. But ifyou're heart is set on a telescope, thenremember this: The attics of the worldare filled with quality telescopes, un-wanted and looking for homes. So con-sider a used telescope instead of a newone. Or as I like to say, an "astro-consumer tested" telescope instead ofan untested one.

With proper care, quality binocu-lars and telescopes will last a lifetime,and beyond. NCA member Gary Hand(Astronomy By Hand) buys, sells, andtrades quality binoculars, telescopes,and accessories, both new and used, atquite reasonable prices (Phone:3011482-0000). He offers substantialdiscounts to NCA members. So call himsoon. 0

Seven Jets From Comet Hale- Bopp

European Southern Observatory PressPhoto 37/96; September 20, 1996

This heavily processed image of C/199501 (Hale-Bopp) is based on aCCD frame that was obtained onAugust 18,1996, by Nick Thomas

(Max-Planck-1nstitut fuer Aeronomie,Germany) and Heike Rauer(Observatoire de Paris, France),observing with the DFOSC multi-mode instrument on the Danish 1.54meter telescope at La Silla, Chile. Theframe was taken at 04:20 universal

time (UT) through an Rfilter (to showthe dust around the cometary nucleus)and the integration time was 20seconds.

The subsequent imageprocessing was perfomed by HermannBoehnhardt (Universitaets-Sternwarte, Munchen, Germany). Itinvolved bias subtraction and flat-fielding, followed by extraction 'of asubframe centered on the nucleus (thearea corresponds to 797 x 797 pixels= 320 x 320 arc-seconds), logarithmictransformation and finally theapplication of a Laplace filter with awidth of 15 pixels.

This procedure suppressesthe smooth structure of the coma andenhances the visibility of the complex,non-symmetrical dust jet structure. Noless than seven jets can be clearlyseen, emanating from the nucleus.They are caused by the reflectedsunlight in dust grains which areemitted from vents on the surface, dueto the pressure of outstreaming gas.

At the time of theseobservations, Comet Hale-Bopp was2.761 astronomical units (AU) fromthe Earth and 3.392 AU from the Sun.The appearance of the dust jetstructures changed very little over aperiod of 3 nights, suggesting a longrotation period.

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National Capital Area Astronomical EventsFree Lectures at the Einstein Planetarium and Other Daily Events

National Air & Space Museum

202/357-1550,202/357-1686, or 202/357-1505 (TTY)Home page: http://www.nasm.edu

Daily, 10:10AM to 5:45 PM-"Lan-gley Theater continuing movies,"To Fly," four shows starting at10: lOAM; "Cosmic Voyage," fourshows, starting 10:45 AM; "DestinyIn Space," two shows, starting 11:30AM; "Living Planet," one show at3:50 PM; "Mystery of The Maya,"one show at 5:45 PM. Details &Cost: See above numbers.

Daily, 11:00 AM-"SkyQest", De-tails & Cost: See above numbers.

Daily, 11:40 AM to 5:00 PM-"TheNew Solar System", Details &Cost: See above numbers.

Daily, 3:00 PM-"The Stars To-night", Free daily planetarium lec-ture/show.

Through The Month of Decem-ber-Something just for fun. A Spe-cial Space Fiction Film Festival:"Alien Encounters," 7:30 PM, Lan-gley Theater, Saturday, December7, "Invasion of the Body Snatch-ers"; Saturday, December 14,"Stargate"; Saturday, December21,"War of the Worlds"; and Saturday,December 28, "Close Encounters ofthe Third Kind".

Other Area Astronomical Events

December 6,13, and 20, 7:30 PM-"There's No Place Like Home," lec-ture by Howard B. Owen, ScienceCenter (Lanham, MD). Details:301/918-8750. Home 'Page: http://www/gsfc.nasa.gov/hbowens/hbowens_home.html.

December 6 through 22, Fridaysand Saturdays, 7:30 PM, SundayMatinees, 1:30 and 3:00 PM-Ar-lington Planetarium (Arlington,VA) lecture, "Tis The Season." Acelebration of Holiday traditionspast and present, of brilliant winterconstellations, and a star. Details &Cost:703/358-6070 or 6019.

December 14, 7:00-9:00 PM-"Goddard At Night" sky watchingprogram at Goddard Space FlightCenter (GSFC-Greenbelt, MD)Visitors Center. Bring binocularsand telescope, or look through onesthere. If cloudy, then presentationon astronomicaltopic. Details: 301/286-8981 (TDD 3011286-8103).Visitors Center Home page: http://www.pao.gsfc.nasa.gov.

Mondays Through Saturdays,11:30 AM & 2:30 PM; Ist & 3rdSundays of Month, 11:00 AM-GSFC (Greenbelt. MD) guidedwalking tours of Hubble SpaceTelescope Control Center andNASA Communications Center.Start at Visitors Center.

Mondays Through Fridays, 10:00Saturdays and Sundays, 10:00AM and 1:00 PM-Paul E. GarberPreservation, Restoration, and Stor-age Facility, NASM. Take a tour ofthis facility where they preserve andrestore aircraft as well as spacecraft,engines, popellers, models, andother flight-related objects. Guideconducted tours including the work-shops. Individuals and groups arewelcome. Reservations must bemade two weeks in advance. Noheating or air conditioning so dressaccordingly. Details: 202/357-1400, or write to ATTN: Reserva-tion Office, Education Services Di-VISIOn, MRC-305, NASM,Washington, DC 20560.

"Deep Night" Periods ForStar Viewing

Dan Costanzo's article on "Deep Night"periods will not be available this month.Dan has been sick. Look for his articleto appear again in the January issue ofStar Dust. If you are planning on star-gazing and would like information, youcan contact Dan at the numbers below.Information: Daniel Costanzo,703/841-4765.

"Sky Watch"Look for the "Sky Watch" column inThe Washington Post "Style" section onthe first Wednesday of each month. Itlists many current events for the month.

"Observer's Handbooks"Copies of the "Observer's Handbook"for 1997, published by the RoyalAstonomical Society of Canada, will beon sale for $12 apiece at the December7th NCA monthly meeting and at allsubsequent meetings until they are soldout. Please bring a check made out to"National Capital Astronomers" ratherthan cash. If you wish to buy a copy butcannot attend the meeting, call JeffNorman at 202/966-0739 to make ar-rangements for pickup. Thanks.

Newsletter Deadline forJanuary Star DustDecember 15, 1996

***DO NOT BE LATE!!!***

Send Submissions to Alisa & GaryJoaquin, at 7821 Winona Ct.,Annandale, VA, 22003, Leave a mes-sage on voice mail 703/750-1636. Textfiles or graphic files in .GIF or .TIFFmay be sent via E-Mail toajglj@erols.com or fax submissions to703/658-2233. No submissions will beaccepted after the 20th. There will beno exceptions. We need a reasonableamount of time to design, edit, and re-view this newsletter. Though we haveadequate time and resources to publishthis newsletter, it is even more impor-tant this year to receive submissions ontime. We would appreciate everyone'shelp in this matter. Thank you.

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National Capital Astronomers, Inc.SERVING SCIENCE & SOCIETY SINCE 1937NCA is a non-profit, membership supported, volunteer run, public-service corporation dedicated to advancing space technology, as-tronomy, and related sciences through information, participation,and inspiration, via research, lectures, presentations, publications,expeditions, tours, public interpretation, and education. NCA is theastronomy affiliate of the Washington Academy of Sciences. Allare welcome to join NCA. For information: 3011320-3621 or703/841-4765.

SERVICES & ACTIVITIES:Monthly Meetings feature presentations of current work by re-

searchers at the horizons of their fields. All are welcome; thereis no charge. See monthly Star Dust for time and location.

NCA Volunteers serve as skilled observers frequently deployingto many parts of the National Capital region, and beyond, oncampaigns and expeditions collecting vital scientific data forastronomy and related sciences. They also serve locally byassisting with scientific conferences, judging science fairs, andinterpreting astronomy and related subjects during public pro-grams.

Discussion Groups exchange information, ideas, and questions onpreselected topics, moderated by an NCA member or guestexpert.

Publications received by members include the monthly newsletterofNCA, Star Dust, and an optional discount subscription to Sky& Telescope magazine.

NCA Information Service answers a wide variety of inquiriesabout space technology, astronomy, and related subjects fromthe public, the media, and other organizations.

Consumer Clinics on selection, use, and care of binoculars andtelescopes, provide myth-breaking information, guidance, anddemonstrations for those contemplating acquiring their firstastronomical instrument.

Dark-Sky Protection Efforts educate society at large about theserious environmental threat oflight pollution, plus seek waysand means of light pollution avoidance and abatement. NCAis an organizational member of the International Dark-SkyAssociation (IDA), and the National Capital region's IDArepresentative.

Classes teach about subjects ranging from basic astronomy tohand-making a fine astronomical telescope. NCA's instruc-tors also train educators in how to better teach astronomy andrelated subjects.

Tours travel to dark-sky sites, observatories, laboratories, muse-ums, and other points of interest around the National Capitalregion, the Nation, and the World.

Discounts are available to members on many publications, prod-ucts, and services, including Sky & Telescope magazine.

Public Sky Viewing Programs are offered jointly with theNational Park Service, the Smithsonian Institution, the U.S.Naval Observatory, and others.

NCA Juniors Program fosters children's and young adults'interest in space technology, astronomy, and related sciencesthrough discounted memberships, mentorship from dedicatedmembers, and NCA's annual Science Fair Awards.

Fine Quality Telescopes up to 36-cm (l4-inch) aperture areavailable free for member's use. NCA also has access toseveral relatively dark-sky sites in Maryland, Virginia, andWest Virginia.

YES! I'D LIKE TO JOIN THE NATIONAL CAPITAL ASTRONOMERS

Enclosed is my payment for the following membership category:[ 1 Regular

[ 1 Sky & Telescope and Star Dust. ($51 per year)[ 1 Star Dust only ($24 per year)

1 Junior (Only open to those under age 18) Date of birth: _Junior members pay a reduced rate.[ 1 Sky & Telescope and Star Dust. ($42 per year)[ 1 Star Dust only ($15 per year)

First name Middle Last name(--)------Telephone

City State ZipStreet or Box Apartment

If family membership, list names of additional participating immediate family members in same household, with birthdates of allthose under 18 years old: _Note: If you already subscribe to Sky & Telescope, please attach a recent mailing label. You may renew this subscriptionthrough NCA for $22 when it expires.Make check payable to: National Capital Astronomers, Inc., and send with this form to:NCA c/o Jeffrey B. Norman, 5410 Connecticut Avenue, NW, Apt. #717, Washington, D.C. 20015-2837.The following information is optional. Please indicate briefly any special interests, skills, education, experience, or otherresources which you might contribute to NCA. Thank you, and welcome to NCA!

Page 9

Getting to the NCA Monthly MeetingMetroraiI Riders - From Medical Center Metro Stop: Walkdown the hill, pass the bus stops and turn right at the anchoronto Center Drive. Continue uphill to Building 10 (walkingtime about 10 minutes), the tallest building on campus.Also, the 12 bus line connects the Bethesda (7: 16 PM) andNIH (7:23 PM) Metro stops with Building 10 (7:25 PM).

To North China Restaurant - Take Wisconsin Avenuetoward Bethesda and bear right onto Woodmont. FollowWoodmont to Old Georgetown Road and make a right. Therestaurant is a few blocks on the left (7814 Old GeorgetownRoad). Alternatively, turn right on Cordell from Woodmontand proceed a few blocks to Old Georgetown, where youwill come out right near the restaurant. There is parkingaround the corner on a side street.

Star Dust is published ten times yearly (September throughJune) by the National Capital Astronomers, Inc. (NCA), anonprofit, astronomical organization serving the entireNational Capital region, and beyond. NCA is the as-tronomy affiliate of the Washington Academy of Sciencesand the National Capital region's representative of theInternational Dark-Sky Association. NCA's Phone Num-bers: 301/320-3621 or 703/841-4765. President: HaroldWilliams, 301/565-3709. Deadline for Star Dust is the 15thof the preceding month. Editors: Alisa & Gary Joaquin,7821 Winona Ct., Annandale, VA 22003, 703/750-1636,E-mail: ajglj@erols.com. Editoral Advisor: Nancy Byrd.Star Dust © 1996 may be reproduced with credit toNational Capital Astronomers, Inc. Map Not To Scale

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National Capital Astronomers, Inc.If Undeliverable, Return toNCA c/o Leith Holloway, Apt. #M-lO10500 Rockville PikeRockville, MD 20852-3331

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EXp. 3/97Dr. Wayne H Warren} Jr8001 BRETT PI..GREENBELT MD 20770-3001