OccdhtlM3NewstelterVolume II, Number 10 january, 1981

Occultation Newsletter is published by the International Occultation Timing Association.Editor and Compositor: H. F. DaBo11; 6 N 106 White Oak Lane; St. Charles, IL 60174; U.S.A.Please send editorial matters to the above, but send address changes, requests, matters ofcirculation, and other IOTA business to IOTA; P.0. Box 596; Tinley Park; IL 60477; U.S.A.

NOTICE TO LUNAR OCCULTATION OBSERVERS

L. V. Morrison

On 1981 January 1 the international centre for thereceipt of timings of occultations of stars by theMoon will be transferred from HM Nautical AlmanacOffice, Royal Greenwich Observatory, England to As-tronomical Division, Hydrographic Department, JapanFrom that date observers should send their lunar oc-cultation reports and any correspondence connectedwith lunar occultations to the following address:

paho1. by contacting Sr. Francisco Diego Q., Ixpan-tenco 26-bis, Real dc Ids Reyes, Coyoacdn, Mexico,D.F., Mexico. Currently, however, the Latin AmericanSection is experiencing problems with funding, andfor the time being, it may be necessary for would-beIOTA/LAS members to subscribe to the English-lan-guage edition of o.n., or to join the parent IOTA.

IOTA NEWS"'

David W. Dunham

Astronomical DivisionHydrographic Department

Tsukiji-5Chuo-ku, Tokyo

104 JAPAN

<~

The layout of the report form may be changed a littie and observers should write to the HydrographicDepartment for new forms. During this change-overperiod it is important that observers should givetheir full postal address, positions and descrip-tions of their telescopes on the report forms, otherwise there may be considerable delay in reducingtheir observations.

Observations of occultations of stars by planets,satellites or minor planets should continue to besent to HM Nautical Almanac Office.

FROM THE PUBLISHER

For subscription purposes, this is the fourth andfinal issue of 1980.

O.n.'s price is $1/issue, or $4/year (4 issues) ineluding first class surface mailing, and air mail "...Mexico. Air mail is extra outside the U.S.A., Can."-da, and Mexico: $1.20/year in the Americas as farsouth as Colombia; $1.68/year elsewhere. Back is-sues also are priced at $1/issue. Please see themasthead for the correct ordering address.

IOTA membership, subscription included, is $7/yearfor residents of North America (including Mexico)and $9/year for others, to cover costs of overseasair mail. European (ordinarily excluding Spain andPortugal) and U. K. observers should join IOTA/ES,sending DM 12.-- to Hans j. Bode, Bartold-knaustStr. 8, 3000 Hannover 91, German Federal Republic.Spanish, Portuguese, and Latin American occultationobservers ordinarily may have free membership inIOTA/LAS, including Occultation Newsletter en Es-

As of 1981 January 1, H. M. Nautical Almanac Office,at the Royal Greenwich Observatory, England, willdiscontinue collecting observations of lunar occul-tations. After that date, observers should sendtheir reports to the new International OccultationCentre in japan, as described in this issue's leadarticle. This poses a problem for 1980 reports,since most observers have been filling out theirHMNAO occu1tation report forms as they make theirobservations, and new report forms have been de-signed by the I.O.C. Any reports sent to HMNAO willsimply be sent on to Japan. Since the I.O.C. reportforms are rather similar to HMNAO'S, the I.O.C.might accept reports, for 1980 only, on HMNAO'sforms. I have written to the I.O.C. asking if thisis all right, and hope to publish their reply in thenext issue, which we hope to distribute early inFebruary. In the meantime, you might hold onto your1980 data until we publish the decision. Also, thenew I.O.C. report forms should be available by then,so that if you have not already filled out an HMNAOform, you could use the new forms instead. In anycase, start using I.O.C. forms as soon as possible.

Guillermo MallCn reports continued difficulties withhigh demand for use of the computer at the Universi-dad Naciona1 Autonoma dc Mexico, so that graze pre-dictions for Latin American section members arestill available only through membership in the mainI.O.T.A. Ma11Cn is applying for resumed support ofIOTA/LAS operations in Mexico City, hoping for com-puter access perhaps in April, hopefully in time tocompute graze predictions for the second half of1981. If you need the total occultation predictionsfor 1981 which were originally supplied by Mdllen,write to me at P. 0. Box 488, Silver Spring, Mary-land 20907, U.S.A. If there is a large demand forsuch predictions, I will send magnetic tape data forLatin America to Walter Morgan so that he can supplythem.

The American Ephemeris and Nautical Almanac has beensubstantially revised for 1981, and renamed The

174

Astronomical Almanac, published jointly by the RoyalGreenwich and U. S. Naval Observatories. There isan error in the 198] edition: The ephemerides givenfor the four main minor planets are 1abe11ed as"astrometric, 1950" when in fact they are apparentof date. Starting with the 1982 edition, theseephemerides actually will be astrometric, 1950.

The errors in USNO'S XZ catalog, described in o.n. 2(6) 58-60, have still not been corrected. Hence,the magnitude of X05404 is still given as 5.8 in theUSNO total occultation predictions for 1981, al-though the star's magnitude is actually 11.3. Thom-as Van Flandern has recently programmed a method forupdating information about non-SAO stars in the XZcatalog. Sometime during the next few months, Iplan to write a program to read my magnetic tape ofK - XZ matched data and generate input data to cor-rect the bad magnitudes and spectral types in thecurrent version of the XZ. So if X05404 is occultedduring ]982, its magnitude should be listed correct-ly as ]1.3 in the USNO predictions for that year.

Our first publication on Solar variations fromeclipses, "Observations of a Probable Change in theSolar Radius Between 1715 and 1979," has appearedin Science 210 (4475) 1243-1245, issue of 1980 De-cember 12. We have not yet received reprints, buta large supply should be available soon, hopefiilltto be announced in the next issue of o.n. Copieswill be sent to a]] observers who reported observe-tions, or otherwise were involved in the effort,near the edges of the 1976 and 1979 total eclipsepaths. More recent analyses were mentioned on p.102 of the last issue, but further more refinedcalculations have shown no significant variationbetween the total eclipses of )979 and 1980, butperhaps a small expansion from 1976 to ]979. J.H.Parkinson, L.V. Morrison, and F.R. Stephenson hawpublished an analysis of central eclipse timings 1·a paper, "The Constancy of the Solar Diameter ovejthe Last 250 Years," in a recent issue of Nature.They found no significant variation, but their ob-servational errors are greater than ours sincetheir method does not have the advantage of thegrazing geometry and is much more strongly affecttmby random and 1ibration-dependent systematic errot-in Watts' Lunar limb correction data. They pointout that our result depends largely on the ratheruncertain location of the observer at the northerrlimit of the 1715 eclipse. However, we have recer.'-1y found well-documented observations at both edg€of the path of the 1925 January 24th total eclipse.analysis of which reveals a Solar radius over 0:'6larger than that derived from the recent eclipses,and slightly larger than the value we derived for1715. The 1979 eclipse occurred three Saros cyck-.after the 1925 eclipse, so the geometry and 1ibra-tions were similar. In 1979, two contacts and onebead event were produced by three Lunar valleyswhich produced three of the four defining contactsin 1925. An analysis of just these three 1979events confirms our earlier analysis of a correc-tion near zero to ±0:'2 accuracy, and we have asimilar less accurate result from three 1980 eclipsebead timings. It appears that we have strong evi-dence for a substantial decrease of the Solar ra-dius from 1925 to the present. The variations donot seem to be secular, but rather may be irregularor partly periodic, perhaps with time scales of tensof years, perhaps related to the sunspot cycle.

The inclusion of K-catalog stars in the regular USNOtotal occultation predictions for 1981 was mentionedin the last issue. The calculation of J-catalogpredictions for 1981 will be delayed until February,to allow time to create a new catalog with Praesepe-cluster stars, more southern stars from the SouthernAstrographic Catalog project, and more northerlystars in the northern Milky Way from the Astrogra-phic Catalog. These stars are not in the current J-catalog, but begin to be occulted during 1982 as theLunar node regresses. The delays in doing this workhave resulted from the usual new-year predictioncrunch, greater this time due to the much largernumber of planetary occultations during 1981, and myinvolvement with favorable but time-consuming aster-oidal occultation observations late in 1980.

John Phelps produced and distributed the very usefulIOTA membership list of 1980 September. I foundonly a few errors, such as "Chris Aikhan" (should be"Chris Aikman"). Dr. A. a. Nefedjev, who computedgraze predictions for Soviet observers, died a fewyears ago. Just after the list was produced,Richard Nolthenius moved to 1137 N. Clark, Apt. 5,still in West Hollywood, CA, and Derald Nye moved toRoute 7, Box 511, Tucson, AZ 85706. The geographic-al listing in Part II should be most useful for con-tacting other observers in your area.

Byron D. Groves, 601 N. Parkcenter Dr., Suite 10],Santa Ana, CA 92705, wrote to me in September askingagain if I.O.T.A. would like to meet with the West-ern Amatetir Astronomers in Orange, CA, from 1981July 23 to 26, and assumed that we would not if hehad no reply by Thanksgiving. I had hoped that thisissue would ha:ie been distributed before then, tosee if there was any interest in at least a regionalIOTA meeting. I did not reply, since the dates con-flict with a possible trip to observe the 1981 July31 Solar eclipse, and the distance is too great forthe other IOTA officers. If there is some local in-terest, an at least informal regional IOTA sessionmight still be arranged.

Last August 12th, Russ Genet, M. D. Overbeek, WayneWarren, Hark Trueblood, and I met in Silver Spring,MD, to discuss photometry of occultations. RussGenet, 1247 Folk Rd., Fairborn, Oh 45324, phone513, 879-4583, is co-editor of the i.a.p.p.p.c.(International Amateur-Professional photoelectricphotometry Communication), the 2nd issue (1980

Sept.) of which contained a summary of their firstannual symposium held in Dayton and Fairborn justbefore the 1980 Apollo Rendezvous in June, shortsketches of the backgrounds of the first 51 membersof I.A.P.P.P., and articles with titles such as"A Solid State Photometer," "A photoelectric DataReduction Program in BASIC for Microcomputers,"and "High Speed Spectroscopy of Algol Systems."

The next issue will be published a few weeks afterthis issue, and will contain mainly several reduc-tion profiles of grazing occultations, findercharts and maps for some of the early 1981 planet-ary occultations, and probably less text than thisissue. Articles on new double stars and on grazesreported to IOTA may be delayed until the followingissue #]2 scheduled for early April, with a mid-March deadline for receipt of material by DaBo11.Joseph Carroll, Minnetonka, MN, hopes to have dc-cu1tation tallies for two or more recent yearsready for that issue. He notes that his tally work

115

" is considerably facilitated if observers put theirHMNAO station/observer/telescope codes on theirannual occultation count coupon.

GRAZING OCCULTATIONS

David Id. Dunham

Reports of observations of grazing occultationsshould be sent to me at P. 0. Box 488, SilverSpring, Maryland 20907, U.S.A. If possible, a copyof the report should be sent to the InternationalOccultation Centre (I.O.C.), Astronomical Division,Hydrographic Department, Tsukiji-5, Chuo-ku,Tokyo, 104 japan, and it should be stated on the re-port whether or not a copy was sent to the I.O.C.If no such indication is given, it will be assumedthat no copy was sent, and I will make and send acopy to I.O.C. Graze reports should no longer besent to H. M. Nautical Almanac Office at the RoyalGreenwich Observatory, England. I have quite a fewreports of 1980 grazes which need to be sent to theI.O.C., and am looking for a volunteer to tran-scribe these reports onto the new I.O.C. forms.

In late October, the I.O.C. sent copies of their" proposed report forms to H.M.N.A.O. and to U.S.N.O.

asking for comments. I got a copy of USNO'S copyand wrote a letter to I.O.C. enclosing a copy ofIOTA'S form, and suggested several relatively minopmodifications that could be made to include all ofthe information now requested on IOTA'S form.Even if they do not change their form, a large are.:is provided for comments, and part of this can beblocked into specific columns for any of the addi-tional information which IOTA may want. In anycase, IOTA will soon abandon its current forms forgrazes and use the finally-adopted I.O.C. form, pe-haps adding some columns in the comments section anoted above. When the new forms become available,they will be distributed First to active graze ob-servers and later to all IOTA members.

The corrections to the USNO graze predictions des-cribed on pages 95 and 96 of the last issue shouldno longer be applied; they have been taken care ofwith changes to the ACLPPP profile printing prograzsent to all computors for the 198] predictions.

PLANETARY OCCULTATION PREDICTIONS

K-" David bl. Dunham

Predictions of occultations of stars by major andminor planets, all but one during 1981, are given ii}two tables. They are like the tables described ino.n. 2 (2) 16-18, except that in the second table,the geocentric angular velocity of the object in dc-grees/day is listed with the position angle of mo-tion under the comnon heading "Motion," and the tax-onomic type of asteroids is given in a new columnbetween the columns for the radius of sphere of in-fluence (RSOI) and motion.

The taxonomic types are those given in the TucsonRevised Index of Asteroid Data (TRIAD) as publishedin the book Asteroids (see p. 104 of the last issue)and are described on pages 783-806 of that book.Based on new comprehensive observations, the type of(216) K1eopatra has been revised to "M." The typesare determined mainly from observations of albedo(reflectance) and spectral characteristics (color),

and are named from meteorites with similar proper-ties. Hence, specific mineralogies are implied,which may not be completely correct. But most as-teroids of a given type probably do have similarcompositions. The six types are described below:

C low albedo, carbonaceous_S moderate albedo, silicate

M moderate albedo, metallicE high albedo, ensUtite achondritesR moderate to high albedo, red (iron silicates)U .u.nusua7, not in the other"five categories

Composite types, such as "CMEU," only mean that theobservations exclude the other types.

A complete description of the S-column in the secondtable (source of star's position) was given in o.n.2 (7) 62-63.

Most of the events in the table were found by GordonTaylor at the Royal Greenwich Observatory and pub-lished in his Bulletin 20 of I.A.U. Comission 20'SWorking Group on Predictions of Occultations by Sat-ellites and Minor Planets. Derek Wa11entinsen, com-paring the SAD catalog manually with astrometr'icephemerides supplied by me, found the events on thefollowing 1981 dates and published predictions ofthem in Contribution No. 2 of the James-Mims Obser-vatory (see p. ]04 of the last issue): jan. 23,March 6 (216 Kleopatra), March 19, June 26, July 2,July 15, Nov. 28 (624 Hektor), and Dec. 14. He alsoindependently found many of the events listed byTaylor, and also found ten events which miss theEarth by less than one arc second, so that, due tostar position or ephemeris error, an occultation maybe visible from the Earth's surface, most likely inthe polar regions. Taylor found two of his events,those on Jan. 26 and on Sept. 19, after he hadissued Bulletin 20, so he sent predictions for thoseevents to observers later. The occultation by Venuson Nov. 17 was first publicized by jean Meeus; SteveAlbers found the occu1tation by Mercury.

About half of the asteroidal ephemerides I use arecomputed from osculating orbital elements computedby Paul Herget at Cincinnati Observatory and pub-lished in the Minor planet Circulars in 1978 (P:os.4361-4390) and in 1979 (Nos. 4824-4825). Most ofthe others were calculated at the Leningrad Insti-tute of Theoretical Astronomy (I.T.A.) and publishedin the Epheinericies of Minor Planets (E.M.P.) for1980 or 1981. For many events, elements from bothsources are available, so that I can make two separ-ate predictions. For events on the following dates,the ephemerides differ by less than 0!'4 and less .than 2.5 minutes in time, smaller than the expectederrors relative to the occulted stars: Jan. 23,Feb. 1 (18 Melpomene), March 6 (54 Alexandra),March 19, April 2 (36 Atalante), April 4 (83 Bea-trix), April 15, April 20, April 26 (13 Egeria),April 29, May I], May 14, May 17, May 20, May 21,May 26, May 30, Aug. 9 (354 Eleonora). Aug. 26 (70Panopaea), Sept. 6, Oct. 7, Nov. 2, Nov. 18, Nov. 28(16 Psyche), and Dec. 14. Larger ephemeris differ-ences are given in Table 3, in the sense I.T.A. mi-nus Herget, except for one noted case. The valuein the shift column gives the path differences inarc seconds measured perpendicular to the asteroid'sgEocentric motion; the letter following it tellswhich direction the occultation path will be dis-placed on the Earth's surface from the nominal (usu-ally Herget) prediction. The value in the At column

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3692

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1211

480.1

70.6

orbits by Herget and two by I.T.A. all satisfy late1977 observations; the earlier I.T.A. orbit, used byTaylor and by me, gives residuals in declination of

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118

0!'4, five times smaller than those given by theother orbits, which say that the June 5th shadow ofPatroclus will miss the earth's surface by 4!'5 or21,000 km. Some recent astrometry is needed toclarify the situation for Patroclus, as well as forsome of the other large ephemeris disa reements inTable 3 (p. 120). The differences in ?18) Melpome-

ne's orbits become apparent only when the asteroidis closest to the earth near opposition in mid-1981.

The occultations by Uranus and byby Arnold Klemola, Doug Mink, andscanning Lick Observatory plates.events for 1981 through 1984 will

Neptune were foundjim Elliot byTheir results for

appear soon in the

~cqo<oocrloomLcj~wc'jcDc'mocvcnc")ajc'ja^cj~LDc"^DLsj<"mcocnGmwm

~ m

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. C

anada

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=

"m = ¢5+" Q) ·m

V) om · n+· S- CU m© » CJ S-m «3 ·r 4-' cU© * S- on ·r-C Q) = L.CU " E<c d)

C.J C.J <E .D

Gc,r) C.)U7S. -Cl 3 ·ma) = C4-~+J a. " n 'm mcn a) V) CJ X.(I) CC K· m -b'3 m Cl. =

C >,·m 0>· · ^ In X- = G)·m © C'S Q) S-·r m uuo q) =

ecS on ru~4"4"3 AS r-- · " V) S-¢T3m cUM Q) CJ=<E= 3 C

c,nCg·

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n pmV) "m

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¢5 U 4" ©> m U) 3CI Cl. qj co= V) 3 =

GC··p a: melS V) C'-·

F V) ru= 'mG) V).a · <

=ell cn a} ·

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V) "m «·^ S. " elSV] a) >,·m

% qj & E2 ®m a. ¢5 3 &- ="D CI L).m ¢1lj » O= £.m+""m—"o~ = X &^~" m

IJJ 4- O ^ ~·" mC = CU " "U) m C G.) V)C X. n C C-e C6·ecS QJ elS S- ·m S- ·r··r .G ·m qj ·r 4- "r=+" &.+" m<C mG = qj Uj 3 3m O -Q qj tv · CUU') Uj~ 3= ==

Astronomical jour-nal; I thank the au-thors for providingme with preprints.The central dura-tions for these e-vents usually aregiven in minutes ra-ther than seconds,as given for most ofthe other events.These occultationscan only be recordedphotoe1ectrica11y,in infrared methaneabsorption bands.Hence, the magnitudedrop (Am) for theseevents is for the I-magnitude band, notV, as for the otherevents. The visual(V) magnitudes givenfor these stars arevery approximate;more accurate mea-surements were madein the I-band. Pre-dicted times for ma-jor observatorieswill appear in thea.j. articles. Inthe case of Neptuneon Feb. 7, the plan-et will not occultthe star, with mini-mum geocentric sepa-ration being 2'.'2;however, the starcould be monitoredto discover possibleclose rings. Theoccultation of May24, also marked with"R?," is in the samecategory. The May10 Neptune event isvery favorable, andthe one by Uranus onApril 26 is the sec-ond best by thatplanet during thefour-year intervalcovered by Klemola,Mink, and Elliot.

A map showing mypredicted paths ofasteroidal occulta-tions during 1981 inthe U.S.A., southernCanada, and northernMexico will be pub-lished in the 1981january issue of Sky

'

119

k=e-

K_

and Telescope [Ed: Actually, it does not appear in are being computed by joseph E. Carroll, 4216that issue]. A similar map of the U.S.S.R. has been Queen's Way, Minnetonka, MN 55343, telephone 612,prepared and sutmitted for publication in a Soviet 938-4028. I recently supplied him with input datajournal. Maps and finder charts for the early 1981 for the 1981 events, and we plan to compute and dis-events will be published in the next issue of o.n. tribute these predictions to everyone on the IOTA

mailing list. If you want predictions for a differ-As noted in the last issue, local circumstances of ent station(s), send coordinates to joe Carroll.asteroidal and planetary occultations and appulses The local predictions are planned to supplement the

data given in theI— -

= , #¢m'o<mo]mmcn<nc^o^mLnm~)<<Dm_o¢Dr^n<D©c')m¢cvej~©cn¢

tables in this arti-<=o~<o=«~<wmm<~~ow%_<wmmNmm~wm~N<~ cle.

U QLjJ Q) m'cvcnmc")omm"—¢«jm·¢o~mm^D~©~mcDLcjoomLAL£)~mQD©~©©o~c'j~Cl cq CV In C'J I e7cvc'j r—¢\jC'jcqc'j I CV I CV C'J m r- DJ G") C'J ~ CVqc 0 s i i i i t i ' ' ' ' ' More on Observing< r"^c>mmm(D«j~^r7omm^mmLsjc"j~Lcjr^ommo~Lsjmmommo=Lc>m Methods : Some notes

a. . E~om~mw<mwmm^~%m%o~m~m~©mw^~momwwmmmm~^ on observing tech-mC mmomo<~m©~oom<=womowommmmw¢w~~wmwwm<m< , ,

a. . = niques are given be-« mLocv¢Lc>c")Nc4cDLs^"^oLc)<"o~^mcv«nc)QcDommLnoujmmmNomujooo ,< ~m m ~ cv m dj ~ Cxj CNl «1 cv m ~ Cnj __~N~— — c'j low; these will sup-

© c·7 c·j c> g) ~cqf)qw¢dq cj = C»~~Om m· co o _ m- m- cn 'n piement and amplify

t a a a a Kcs(ymaaa a cS Laata a t cS t t a a a some of the proce-EE F- I I I I I I I I i I I

& e cn 'D ~ ~ ~ C;j ~ DJ m- ~ c\j _ coLncOm·m ·± uj m co Cyj cv Crj m dures described in

m cv g) 0\ C\J©CQmOWO\ O O ~cnmcr)c·j c'j g") = lcj v) m- c'j qj previous issues of¢ .m cj o 0 ~ oocjcjooo d d 0cjcjcj~ o g) ci Cl ~ o c) o o .n. and Sky andjr) u7 i i t i i i i i i i i i~m m cd cn lcjlcjlcjcvcjisj Lei ~ cn m m c'j co CFb Ln m co m c) _ _ Telescope .<1 D W LO CO 040LCJ~mCV IS) VD LCJ cn DO CO ·T ^ CJ cn cn ~ <r Lei COa. Z LEI xr CD UJ~LS)~¢LCJ CD ~ CTb C'J ^ VD CV LO LO LA G") LO C>J

_ ~ m ^j ej _ (>J _ — — — In some cases, theSS2 °r'jcn m ·t~ujc>j<4d m lo ~ © Ljtj o is) lcj ~ ~ 4cj c;j m 'xi star will disappear

2 c\j mC')~CXjC\j n ^j ej cn C\j4~ = = =~~==== = = = = = v) == ~~ = = :~~ = = = and reappear in

c,n| xumnxox^wnwxmmaxxxo4jxxax<oxxmxw»*o*xxx steps because it is4- <m~©~Nw=~~mwo~m~Nm~¢mmmm~¢w~¢mmm<m~momm a previousl y unknown

m ON¶~OwD=onOOm~mOOO~_m~<OOoooO~~O~OO— close double star.Ei! Q) The magnitude dropLA-I E ~~r·.~Nm=c")cDLc)o^c^DLsjm<c\jc")~mmujm~ocom-~~mmLDo~~E ·m Le') lc> Cyj un ~ c·j ODD m C\j m-cncn~~ m ~ Dj CYIC>jN~DjLD_ CF) for each step will<1 F-~c3 ~~~~oc")o\mmmocqcmor^jm¢Dm~j^m>^")=cnmc")mLs)m~<-cnw=cDmN be less than the to"

zl m0c')c"7mcDLD_m-mmu)QDm-cnLD~ls)m·ow(D©mcvmoK.m·cDmr7o\o\cms)mw ta1 drop ii sted inQC Le) ^J Le) ^ ~ C>J _ ~ ~ m- C'7 mC"jW<©LCj C'J C'J c\jc'jc\jmcnc")N^LnmcmA

:5 " " " " " " the table; events-j mm¢mmwo©o~©^mm^mm¢mowmm~mmmNmwmwmmmm—~~ involving a fainteruj = Qm"r^voc")o'Doo~cnoooc'jc"^c)cv~o~o=~¢n~mmn~~ln~cnf- d · · · · · · · · · · · · - · · · · · · · · · · · · " · · · " · · · ' · · " · ' component may beV) O=QOOOOOOOOOO~OOOOO=OO0OO=O0OOOO=0OOOOO ,

cji ,l g, >. difficult to see.d m For some events, the

QC ~m-m¢or-mx)e)ajcNLc)c>joqc>jcno 'm'~r^")cocjc?^Daj—Qc)ajcYjK^cjcj~~Ls)o~~ .· '<rLc)©m~m-<mvD¢¢'jocD^cr)© cDc\jLc)=~c'jmc'j¢oqLs)<-m<ux)mc"^cj~m" disappearance or re-

d m·tnrmx)majwc"j~c»¢o~vD coUjcjcT'bc'jLc)o~cYIcv~c:U<r'Emje)~c")ooc>j~= ~ Crj 0\ NlDC>j~~M-~ '<r <r lo r-K^r)cncvm<us)cv ~Lc)cvc')koc>jcn~c'j¢ appearance will be<1 D O m m m

mu>j=ocr)_cc)<ujc\jm-«jwc»= mcv~r^c)ooc'jLc^o^oj^Lom¢¢oej<— gradual due to the% ejc\jcjLcjcrjcjCjO~m~c4cv~O~ c'jc4cvoocvoojocno~~onj~ocnN~No

I t + J + + i+ + + + + + f + j + t I i + + I I + + + + I + I I + i+ + I + 'f- angular size of theo ~ c>~ cd is) nj aju3c")^o<co^ LDLSJOC>mChW co m· —coco©^~ ~ co ~ star and/or diffrac-= ~ m" C) C'J O ~ ~c"j^=Ls)ajcT~" cncoc'jcncjc'j m- ej Lsjm-'cjc^0 ~ cq (4j .c»< cv cv ~ 0'\ cv~cnonwe—^ m<c'jcrjmc3~ w Lit) lsjco<~¢4d c>j m" m" tion of the star's

ci') o low 0\ m' ¢= ISl guxjcdqo^q0©·± OmOCOqj«~ co m cvtm~u>ajo Dj m C^a coco ~ nr ¢\j ·± mtc)ob^u)cm0 mm<-~<aj ls) o majuj Dj (XI o light at the edge of

~ Cxj ~ ¢—— r—— ~ T— ~ ~ ~ m ~ m" ~~~ ~

° the asteroid. TrymC m¢Dcn~rms)¢oc")c")0~mr·^c^om~c'jLDom Lc~ux)m'<r^m"m"c'je~ux)c'jcom= m. ~~mmm~~mmmw©~oo_mo^mm_g<m~~m<mom~~~mo~m tO estimate the dur-C> CV CV ~ «J _ (>J CV ~ C\J C\J C\JC\J ~ ~ ej C'J C>J m~+ oo^mmmo'bo)mmc"jN|^<^D<o©mqDcvommo¢DLD«©Lcjwc\jcn~mw ation of gradual orc> m mc")~Lc)mr')c4cD~w<mmo(Dm'Dcnm<U)<us)c'j~wwmocnLcjmmLs>c'j©w step events .e c3 ~~m~m~wwww~nNNmwmm~n«~wmm~~owmmm~NNm~

0 oooooomoooo=mooooooooo0oooooQoooooooooo ,0 Due to the irregularoutline of aster-i- c»U7wc.j=u)0==oc..j=c.^jc»cnc^^^ncncn=c»c»c»oEcr)c»c^ cr)E=cnu)== oi ds , photoe1 ectric

~ onj~_mc'joc\jc")oc"^c)om~om·cno~~<wcn~~©^ ^rmX)mujO~ observers should tryi— g) r^rjr·.=Lc^cjLcjm~jm-~Gm=mw^m-Lnm¢ncn^mmmm COOcvqOlcjc'j

cn 0\~~~¢n^m·r^oqomc'jLDwm==uj~~wmc")wmm_~Lnmm 'U"'c)<TLc)cnc»M" to obtain accurateLlj Q< C\J ~ cn C>J

= ~ 0, U.T. for their rec-· ~ww~wm~~©m©w~mwm¢¢mo¢om~<¢~Qm~m~w©©m^~ ords, which is not<1 I C'J~C> ·CJ~NOjOCj—OOO«SOO——O—Om—ONOm—O ·~e)oo0 ,

· · · · cj · · · · · · · · - - " " " ' " " " ' " ' " " " " " " " " ' ' ' ' " " ' important for most.J E D O C» ooo0c=oooooc>oooocjcjoooocje)oo=oc\joooe)ooo

" " other types of pho-a. ·m m"mw>^\jLDwLcj¢Dqjm-c'jc'mDmmmm-cms)mc\jc\jm<mmlsj=oommmLnm«mp —qD¢njoLcjmus^cj\DmoLc)o~m"~c")oLms)cYloc\j~¢¢~<mc'j=qmm"—mm tometry . Eventt CXJ ~C>j~LS)~~~CV~CVmNmN mCVmCV~NC'j~e cl) nj markers on manyQC & G CL) Q) ~ qj

o 37 6 'u 'u = elS cu ¢13 " m m chart recorders cank. m Q) cn Q) X a) m ·m n VI CO G aj C ·mq) q) o e o ·~ m m -m e ·~ c e q-j) ·m cl) = ·r- qj aj Eos-ajcm be synchronized man-

= E ^ on l. eel o cu e m in cu CLC E cj x. Q)·m Q)·m rS E.q.c E cu u).q cn o= ci u) c (ii¢5 cn·m O=·m O O.4"O·m %-mO·m QJCL*" E4J C>kj U)·m q)cn+' O·m even a) = a.cj4" cu ?·m e ua11y with short-

~ = ·m4" Ln ono C~ cn Q)— a.p C =4"~ CS ^O Q) q)·r-'C$4"·m qj m Q) Q.·m.0 C~ >,= O^.P O , ,= d) =>,= q) qj_ »cn>no os- q) qj—·~ G.m s->,s-=m :3 s. cum qj q) q) u) Q)m me"" wave time signals ,

* ~xZwmmx=wm<mm<<FmMm~m~j<+<wwm+==xm=a===· mmm"~oc")mmm-mo'boo~Lc)mc')qc"jwm^oLcjmLDmQm¢ co©m·~cjcv© but better accuracy

O W m· i') m m LcjcO=~~mCjr~»Ocv_cn _O¢Omm^rmX) c>j~m-me' can be achieved byZ — cn ·d· ~ ~ ~ m- _ ~ ·d· 'D '<r ~

c')m"LDcvmLrj^mmcvoo¢DKDw<-cD~moc'j~mLcj~~~~~c\j^~mmmo'n<o tape recording theLijmmej _ ~ mCVC'jC'jCVCV ~DjDjNDj ej m~C>jC>jC'j _ 'n time signals and theP- CO<01 =cc:~~~ U)=U}o)U)o)o)U)o}m.a.Q.A.Q.Q.Q.Q.wM~+jw>>>>>> >> uucj audible beep or"L2%8q33£zeEzzeee3g38833888888?2?2?22£882 ·

click of the event

120b

marker. The tape can be developed and measured toobtain ofoi accuracy. Those using digital recordingsystems, if not otherwise synchronized to a clockaccurately calibrated with time signals, can do thesame if a tone generator can be added to the circuitto beep when the digital data collection is startedand stopped. Records of the star and asteroidbrightness should be made before the objects mergeso that any drops after they merge can be checkedfor proper level.

Table 3. Large Ephemeris Differences for 1981.

Aster-Date oid# Shift At

Feb. 5 93 0':50N -0'!13Mar. 13 11 0.705 -].6May 4 93 1.02N -1.0May 9 56 0.015 "4.3May 22 14 0.54N -1.3May 29 11 0.26N -26.9June 5 617 6.44N "7.4june 13 88 0.495 "0.4July 2 31 0.495 "13.]Aug. 7 18 1.40N -2.3Aug. 7 18 2.025 "3.9Aug. 20 409 3.985 -68.6Aug. 27 105 1.47W -].7Aug. 27 105 0.98E +0.0Sep. 4 18 ].50N -2.1Sep. 4 18 2.125 "3.4Sep. 20 14 0.50N "2.4oct. 5 105 1.54W +0.7Oct. 5 ]05 0.25E -1.0Nov. I 471 2.03E -1.7Nov. 28 624 0.125 "27.8Nov. 30 471 4.03N "6.5Dec. 5 40 0.075 -3.3

Notes

Motion very slowHerget - ITA, see above

E.M.P. 1980Earlier I.T.A.See discussion aboveE.M.P. ]980Earlier I.T.A.E.M.P. 1980Earlier I.T.A.

E.M.P. 1980Earlier I.T.A.E.M.P. 1980 - early 11-

E.M.P. 1980 - early IK

crucial step towards making a successful observa-tion. A good, well-aligned finder scope consider-ably facilitates this job, but the process of starhopping can still take a considerable amount oftime if there is no bright star nearby. Those whosetelescopes have setting circles can usually savetime by using them after lining the polar axis withthe celestial pole to within a fraction of the dia-meter of the field of view of the finder. The ap-parent (of date) coordinates of the star are givenin the 2nd table for this purpose. The telescopethen only needs to be pointed to a bright star inthe approximate part of the sky where the asteroidis located, to set the right ascension dial (or touse the difference of the right ascensions of thebright star and the one to be occulted) and to checkthe declination. The coordinates of some brightstars for this purpose can be obtained from the nat-ional almanacs or from sources such as the yearlyHandbook of the Royal Astronomical Society of Cana-da. To make it unneccesary for o.n. subscribers togo to these other sources, a list of the 1981.0 pos-itions of several bright stars are given in conveni-ent form in Table 4. Most of the stars are firstmagnitude, but a few far from the ecliptic have notbeen included, and a few fainter zodiacal stars areincluded in parts of the Zodiac devoid of first-magnitude stars. Since annual precession amounts to50", the table can be used for a few years to anaccuracy of a few minutes of arc.

Table 4. Positions of Some Bright Stars for 1981.0

Star R.A. Dec1..B Ceti Oh 42'!'6 -18° 05'Hamal 2 06.1 +23 22Aldebaran 4 34.8 +16 28Rigel 5 13.6 -8 13Capella 5 ]5.3 "45 59Betelgeuse 5 54.1 +7 24Canopus 6 23.5 -52 41Sirius 6 44.3 -16 41Castor 7 33.4 +31 56Procyon 7 38.3 "5 16Pollux 7 44.2 "28 04Regulus 10 07.4 +12 03Spica 13 24.2 -11 04Arcturus 14 14.8 +19 17cl Centauri 14 38.3 -60 45Antares 16 28.2 -26 23Vega 18 36.3 "38 46Nunki 18 54.1 -26 ]9Altair 19 49.9 +8 490 Capricorni 21 46.0 -16 13Fomalhaut 22 56.6 -29 43

Notes about Tndividua1 Occultations.

1980 Dec 11: This event will occur before subscrib-ers receive this issue, but is included here since,as far as I know, it hasn't been published else-where. A preprint of this information is being sentto potential photoelectric observers, who have per-haps the only hope for obtaining useful data. In-formation about this occultation has also been dis-tributed by the Asteroid Intercept Radio Net. Theoccultation of the star by Jupiter, which is nearlycentral, will not be observable due to the faint-ness of the star, but those in North America mightsee the star's light fluctuate when Jupiter's ringpasses in front of it sometime within the 45 minutes

Paul Maley describes effective methods for visualobservations in his article on p. 396 of the 1980November issue of Sky and Telescope. Most import-ant is learning to find the star several hours, ordays, before the event. The records of this year'events emphasized the importance of quick reflexesReaction times estimated by those who had timed fe»or no previous occultations were invariably short,by over a second in some cases. Valuable experi-ence can be gained by timing some Lunar events.

We have stressed previously that observations shou"·ibe made from closely-separated pairs of stations t.obtain independently-confirmed timings of secondar,occultations. Such observations would be strength-cried if the observers in a pair are separated by e-nough distance :·ic·rCr the direction of motion of theshadow on the ground"to produce a time difference Of"two or more seconds. The motion of the occultingobject can then be approximately determined to seeif it matches that of the asteroid. The directionparallel to the predicted asteroid's shadow path canbe estimated from the regional maps, while the mini-mum desired distance, generally varying from about 5to 30 or more km, can be calculated from the separa-tion of the equal time lines on the maps. For someevents with rapid motion, this becomes impractical;stationing observers within 1 or 2 km of the samepath becomes difficult for distances of about 50 kmor more along-track.

Locating the proper star to be occulted is the most

"

121

\==

<.

preceding the disappearance (the tm j 26 (=) SAD 11 1633star will be well south of the DIAFETER 107 m = C[Cl8ring at emersion). Since materialseems to be concentrated towards 35.ci I ·COthe outer edge of the ring, the O:B - G Ustar's light should be dinned rap- %idly when it first reaches the . h , ering, then slowiY brighten as it °" .~"u_ o Zpasses to the thinner inner por- jyt\"tions. Variations in the star's plight may reveal fine structure ,within the ring. The star will L as Cl ,; ' (. 7,<fdisappear behind Jupiter at 10:21 A " _ , —U.T. on the West Coast, and a lit- T \ 0 p ""

~tie over two minutes later on the I 4A . 'A' " ""¢East Coast. The star will be even T · s C, " i t y " V' ·"with the leading tip of the ansa U 0·1 , kjk3 "

" r p, \7 "

L

of the ring at 9:36 U.T. on the D a,<>C" ">U" }' K"West Coast, when the separation E j\S % ywill be about 14" from Jupiter's 35·C] " ¢ , i

. . . ¶9q * ¥mlimb; an occulting bar in the fo- ti : 4 * " kcal plane would help reduce glare S " %

* "from the planet. The motion is a- d3 >4 " * ,long a line which makes a very ,. p, \shallow angle with the ring. so i.qS \1 t [!'\ sthe time of disappearance at the -j p.u jring varies considerably with geo- "\"3 1 1 I I I I .! Igraphical location. At Washing- 25.C]ton, DC, this time should be abou- 123.0 115.(1 lClj.C] -EE1.(J -85.(1 -73.Cl1Q'17 U.!., but ynqertain by ± !1 longitude %,y ";jj, hyapC " " "

0minutes if a pos]tlona] uncertain- q "§""j6 0] . "' .

ty of 0:'4 (the size of the AGK3 - - . '" e . +SAD shift) is assumed. The Dc? . 0,· ,

4 e

ring disappearance will occur "s" 'Q Oy 0 1·?. · ·'Y 0 ,earlier at more southerly loca- , " r " " d ,

tions. M. I.T. astronomers plan " %d ° :Et "" - " ," · mP

0 9 · '0to monitor the event with the " ° o " (f)uo " ."

, taurusKui per Al rborne Observatory "5 - " E 0° , " g " + .0

near Panama. Doug Mink called ·1' % a , " o el) ° 0 ": ¶ 0'· d 'the event to my attention, but G O q ·

said he did not find it him " iiic35N J ° " · " . " + .self, and did not know when I '4 _ b " " " , !'0 " " ·C

asked how they learned of it " " , , 3 d · " " ' + " .eC + ' e "

+ 0 ·1981 Jan 28: The star is µ . S cl .Capricorni. Mercury' s 6:'2-di - ".' - , c " ° " S " " «"V "ameter disk will be 72% sunlit: 2 I? , (S " : . : ·'5 ,40

the dark-limb disappearance " r " " ' 0P

Dwould be easy to observe except , ,, c.: , . .for the small elongation from '2' ' "- " " " :-' " '"" ""=" ' : "

;q'" u it: 'S S < 3_ .4k L" /"·a" . j 'the sun. The reappearance " " _ , , .might also be observable since '981 jm 26 (365) cordubr sad 111635 .0 "

Mercury' s surface brightness isless than the moon's; its light does ncit appear con- elongation less than 70°, useful last-minute astrom-centrated in a point like an asteroid's. My pre- etry to make a good prediction is impossible. How-dieted southern limit is just south of Hokkaido, ever, since (2) Pa11as is suspected of having a bigwhere the occultation will occur only a few minutes sate11 ite from speckle interferometer observations ,after sunset. some attempt to record a possible occultation might

be made.Mar 19: SAD 118832 is the visual double star A.D.S.8150. The 12th-magnitude companion, 1!'8 away in po-sition angle 75", may be occulted by (48) Doris inHawaii. But the nearly full moon only 7" away willhinder observation of even the primary star.

Apr 7: A 1'.'0 south shift is needed to bring thepath for this down to a region northwest of the Cas-pian Sea, but even there the combination of twilightand low altitude will make observation very diffi-cult. In case of a smaller south shift, putting thepath farther north, the twilight-altitude situationwould be worse. For events like this with the solar

May 10, (2) Pa]1as: Although the solar elongationis small and the path location quite uncertain dueto differences in the star's position, a large ef-fort may be worthwhile since the star is bright andsince Pa11as may have a large satellite.

May 13: SAD 95447 is 72 Orionis.

June 5, (129) Antigone: This probably is the mostinteresting asteroidal occultation of 1981 since SAD142674 is the irregular red variable star S Scuti.It could be as faint as 8th mag., still bright e-

122

nough for relatively easy observa-tion. The star's anqqular diametermay be nearly 0'.'02, /6 that ofAntigone, so even a central disap-pearance will be gradual, lastingover 3s. At the path edges, therewill be partial occultation zonesperhaps 35 km wide. Visual ob-servers should note start and endof gradual events; photoelectricobservations are encouraged toprovide quantitative measurements.

Nov 17: The star is Nunki ((j Sag-ittarii). Venus will not occultanother star this bright until itcovers Regulus in 2044. This oc-cultation of Nunki will occur aft-er sunset in eastern Africa,southwestern Asia, and eastern Eu-rope. Venus' 27"-diameter diskwill be 46% sunlit. Observers atthe center of the occultation pathwill be able to see a spectacularcentral flash in the middle of theoccultation. Venus' spherical up-per aunosphere will focus Nunki'slight so that it will appear as aring of light around the planet,visible on the dark side. Thisphenomenon was first observCd bythe Kuiper Airborne Observatoryduring the occultation of e Genii-norum by Mars in 1976; it shouldbe quite pronounced at this eventdue to the negligible departure otVenus' shape from a sphere. Thecentral occultation line is ex-pected to cross Ethiopia and So-malia; farther west, for examplein northern Brazil and western e-quatorial Africa, daylight mayrender the central flash unobserv-able. Nunki's 9th-mag. companion.9!'0 away in p.a. 244", will be oc-culted 3& minutes before the pri-mary. A gradual disappearance ofNunki reported at a 1919 lunar oc-cultation was more likely due todiffraction than to close duplici-ty of the primary star. Sincethis event is a once-in-a-1ifetitm-opportunity, many may want totravel to favorable areas to seeit, as for more common total solareclipses. Gordon Taylor is work-ing with a British travel firm tO 'organize a trip to east Africa tosee the occultation under the mostfavorable conditions, and to com-bine this with a holiday tour.After observing the occultation itis planned to follow up with op-tional visits to the Tanzania gameparks or a climb of Kilimanjaro.Those interested in joining Gordonon this trip should contact: Ex-plorers Travel Club; 85 Queen St.;Maidenhead; Berks. SL6 1LR; Eng-land.

(to be continued, next issue)

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