The International Occultation Timing Association  17th Annual Meeting at Chamberlin Observatory, Denver, Colorado

Denver, Colorado

April 17-18, 1999


   Chamberlin Observatory      20" refractor


Chamberlin Observatory

Denver, Colorado


Meeting Attendees


  Going over Graze Maps


  Bob Sandy assigning stations


Pre-graze meeting


Highlights of the The 17th annual 1999 IOTA Annual Meeting at the

University of Denver’s Chamberlin Observatory

 Denver, Colorado

  Richard Nugent, Executive Secretary


                The 17th annual meeting of the International Occultation Timing Association was held Saturday  April 17, 1999 at the University of Denver’s Chamberlin Observatory in Denver, Colorado, and at Gates Planetarium  Sunday April 18, 1999. This  meeting place was chosen so that IOTA members and other local astronomers could observe the spectacular graze of Aldebaran by the crescent moon Sunday evening the 18th south of Denver.

Twenty-seven members were present at the  meeting and included: Officers President David W. Dunham from Maryland, Executive Secretary Richard Nugent from Texas, Bob Stencel, Director of Chamberlin Observatory, University of Denver, Dave Miller, Terry Chatterton, Franklin Miller, Pat Rasor, Richard Keen, John Reiss, Jr., Bernie Ansell, Patti Kurtz, Ron Pearson, Dick Dietz from Colorado, Dan Durda and Alan Stern from the Southwest Research Institute in Boulder, Colorado, Derald Nye and Gene Lucas from Arizona, Danny Falla, Frank Anet and wife, Sandy Bumgarner  from California, Don Cooke from New Hamshire, Bob Sandy from Missouri, Rick Frankenberger from Texas, Oliver Staigler from Switzerland, Tom Bisque (of Software Bisque) from Colorado, Don Asquin, Director of Gates Planetarium, Denver, CO,

Prior to the start of the meeting, a brief history of the Chamberlin Observatory was given by its Director, Dr. Bob Stencel. The Observatory was built in the early 1890’s. The main telescope, which was installed in 1894 is a 20” refractor with a 28 foot long tube, made by the famous lens maker Alvan Clark. This telescope is the 12th largest refractor in the world and the largest used on a regular basis for public viewing.  On August 1, 1994, Chamberlin Observatory recently celebrated its 100th anniversary of “first light.” At the same time, the  Denver Landmark Commission proclaimed the Observatory as a Historical Landmark. This designation helps protect the historic facility and enhance opportunities for restoration grants.

Following the introductions, David Dunham mentioned 2 grazes he observed during the first National Amateur Astronomers (NAA) meeting in the Denver area in the late 1960’s. Former President of the Denver Astronomical Society, Derald Nye gave a little history, when he described the IOTA meeting in 1977 which was held in Boulder, CO along with the NAA. 

FINANCIAL REPORT, In Treasurer’s Craig and Terri McManus absence, Richard Nugent read their report which showed IOTA to be in good financial shape with over $6,200 in the checking account. As of April 4, 1999, the previous 12 months did show a $254 loss, however this was due to the choice of dates used for the cash flow analysis. The cash flow report is shown below:

                                Cash Flow Report

                            9/1/98 Through 4/12/99


                       Category Description   


                        Interest Inc                       65.11

                        Member dues               2,671.71

                        Other Inc                          43.09

                        Subscriber                      695.00

                      TOTAL INCOME         3,474.91


                        Card Cost                         20.15

                        Internet Cost                   522.40

                        Office Supplies               117.73

                        Postage                        1,040.94

                        Printing                        1,605.32

                        Reimburse                        99.57

                        Web Site Costs               323.49

                       TOTAL EXPENSES     3,729.60

                       OVERALL TOTAL        -254.69

David Dunham motioned the members present to accept the financial report as it was presented and Richard Nugent seconded the motion. The motion carried without any opposition.

PUBLICATION REPORT - In Rex Easton’s absence, David Dunham updated the attendees on IOTA’s Occultation Newsletter (ON) publication status. At the previous IOTA annual meeting in Nashville in September 1998, it was agreed that the ON would go online for downloading by IOTA members with a password. In return, the annual dues structure would be lowered to $15 /year . Even after going online, ON will still be available in paper form for anybody who wants it to be mailed to them. Of course, for these paper ON recipients, they will need to pay the higher subscription costs which cover printing and mailing.

IOTA MANUAL STATUS - David Dunham reported that Wayne Warren is currently working on updating the IOTA manual. It is now currently on a hidden URL on the IOTA web site. Gene Lucas proposed that the manual be converted to a more user friendly format such as Acrobat Reader. The advantages of this format is that it can be read by readers, but not changed. A discussion by several attendees suggested that two versions of the manual be made, one for beginners, those new to the occultation business, and one for advanced members with experience.  Rick Frankenberger questioned the need for two versions. Gene Lucas added that classical IOTA timing methods, such as those timings made by stopwatches, should be included in the manual  for historical purposes. At the end of the discussion, no firm decision was made on what to do - have one version of the manual or two.

IOTA WEBSITE REPORT - In the absence of Rob Robinson, Rex Easton and  Jim Hart, Richard Nugent briefly described the current status of the IOTA web pages on the internet. The new web page address is synonymous with IOTA’s name, Currently 30 meg of space is available with only 12 meg being used at this time. This should allow room to place many additional IOTA last minute news updates of upcoming events and for future growth. Gene Lucas suggested removing the IOTA logo on the top of the web page to speed up the downloading.

An important step in cataloging all asteroid occultation information in a single place was made with the publication and presentation of the paper  “Catalogs of Asteroidal Occultation Observations and Stars” at the 1998 Division of Planetary Science of the AAS meeting by David Dunham. Other authors of the paper were Wayne Warren Jr., Douglas Faust, Isao Sato, and Edwin Goffin.  This work was supported by NASA grant  NAGW-4714.

In the absence of Paul Maley, Richard Nugent presented to the attendees several key points that Maley wished to bring forward. Currently Trimble Navigation has been loaning to Maley for eclipse expeditions one of their top of the line GPS receivers. Trimble has questioned the future of these equipment loans since their company name has not publicized or acknowledged as much as they would like to see. One such paper acknowledging Trimble Navigation was published in the June, 1997 issue of Publications of the Astronomical Society of the Pacific (PASP), however nothing has appeared since in the way of solar eclipse results.  This is an ongoing problem mainly having to do with funding for data reductions of solar eclipse video tapes. Despite rejected funding proposals in this area, Drs.Dunham and Warren are still seeking such funding.

Another Maley item was the duplication or under representation of  resources during the recent February annular eclipse over Australia.  It was suggested that better coordination of observers prior to such a major event should take place. Email is common now so there should be no real communications issues.

Paul Maley also had noted that the recent asteroid occultation by 580 Selene on March 3, 1999  resulted in a miss for several observers. Even Nugent was 15 miles short of the path after driving 180 miles. This may have been due to a late last minute update on the asteroidal shadow path moving south. Selene is a relatively small asteroid whose angular diameter was less than the expected error of the ACT target star’s position. The event was below IOTA’s criteria for priority updates, but was updated and attempted only because the Southwest Research Institute requested it for their airborne observation campaign; the prediction for most events now relative to the asteroid’s angular diameter are better. In any case, Dunham will attempt to get last minute updates out ASAP but he suggested that observers are encouraged to call the IOTA hotline at 301-474-4945 when in doubt of the circumstances of these types of events. Dunham remarked about a problem with the answering machine on this line, but should have it corrected shortly (the machine was replaced soon after the meeting).  Gene Lucas suggested that in order to help avoid a miss on such events, observers set themselves up along a “fence” perpendicular to the asteroidal path. Dunham pointed out that this is the responsibility of coordination of local observers and he (Dunham) cannot control  how observers along the shadow path set up.

David Dunham mentioned the upcoming IOTA-ES meeting August 5-11, 1999 in Stuttgart, Germany coinciding with the August 11 total eclipse.  IOTA-ES has the largest meetings with an estimated 50-60 persons in attendance over several days.

After a short break, David Dunham showed graze charts for the upcoming April 18, 1999 Aldebaran event. The event was being led south of Denver by Bob Sandy. Dunham mentioned the other planned graze expeditions from Nevada to Kansas.

David Dunham then described some history about his occultation experience to the attendees with his first graze predictions and attempts. On October 30, 1957, Dunham described the Beta Cap event over the Los Angeles area, showing a map of the southern limit computed with the Occult program. On that night, from his home in La Cañada, the 15-year-old Dunham saw the star get closer and closer to the moon, and skim over the mountains above the South Pole, but he never saw the occultation. An occultation had been predicted for the “standard station” in central California. That’s when he realized that he was a short distance on the wrong (south) side of the southern limit of the occultation, and that if he had been a little farther north, at the limit, the star would disappear and reappear among those southern lunar mountains. Dunham thought that it would be neat if someone would calculate those lines, so that one could travel to them to observe grazes, but at the time he didn’t think he would ever be able to do that.

But the situation changed after Dunham took a course in solid geometry at the University of California at Berkeley. For the March 12, 1962 Aldebaran graze, Dunham was armed with sine/cosine, log tables along with a “BIG  CLUNKY” Frieden calculator. He found that the path was to go just south of the San Jose area. He had a 2.4 inch telescope but not a car. He finally located a ride that Sunday evening. While being driven, he was watching the star get closer to the moon. He saw and timed the reappearance at Palo Alto, but missed timing the disappearance - he saw it from the car while crossing the Dumbarton Bridge. Time had run out on the last Aldebaran graze in the U.S.A. during that Saros (actually, Meton) 19-year cycle.

On April 10, 1962 the 2nd graze he attempted, of 64 Ori m = 5.2, was predicted for nearby Concord. Dunham tried to observe the graze but only saw a total occultation. He showed the results to his professor, who told him that he forgot to account for the rotation of the Earth, which changes the angle of the graze on the Moon.

On September 18, 1962 Dunham made predictions of the graze of 5 Tau, m = 4.3. His predictions showed the graze path about 40 miles north of Los Angeles. Dunham could not travel to see this one but he did notify several observers. One of them, Leonard Kalish, traveled from his home in L.A. to the path just north of Castaic Junction and saw several disappearances and reappearances of the star. This was Dunham’s first successful graze prediction, and as far as we know, the first time ever that someone had traveled to an occultation limit and seen a graze.  The first graze observed by David Dunham was on March 31, 1963 of Z.C. 0881, B9, m = 5.9 near Roseville north of Sacramento, California, but timings were not possible since the event was on the sunlit limb. It wasn’t until September that year that he made his first good timings of a dark-limb graze near Davis, California.

Alan Stern asked if there was any predictions of occultations of asteroids by the moon. Dunham said that they are available for some of the brighter ones on the IOTA web page, and in the Occult-generated total occultation predictions in the rare cases when they are observable.

February 16, Annular Eclipse  - Derald Nye  showed an excellent video he took of Baily’s Beads from the northernmost station at the northern limit of this annular eclipse. He took video through  a 1000mm Nikon lens and recorded time signals on VGN 16 Mhz. Numerous beads were seen. The magnitude of this eclipse was 99.2 - making it nearly total.

Olivier Staigler traveled all the way from Switzerland to be at the IOTA meeting. He showed some slides of past solar eclipses he has observed: Mongolia in March 1997, Aruba in February 1998 and Bolivia from November 1994. For the April 1998 double occultation of Venus and Jupiter over Ascension Island he hitched a ride on a military aircraft from the Royal Air Force. Computations show this to be the first double occultation event like this since 547 AD. He met Derald and Denise Nye, and Craig Small there. The slides he presented showed the reappearance of Jupiter’s moon Io, then Jupiter, then Venus. They were taken with a 400mm f/5.6 lens. The last slide shown of the reappearance of Venus and Jupiter was recently published in a Dutch book entitled “Eclips” by Govert Schilling.

In the absence of Bob Collins from Electro Optics (, Dr. Bob Stencel gave spec sheets to the group about a potentially useful device for occultation observers: The I3 image intensifier piece invented by Bill Collins. The I3 piece can give real time video images with a 2-4 magnitude improvement over existing image viewing equipment and low light CCD video cameras on the market today. Specifications include a power source of just 3 volts needed to run the tube which boasts a useful life of 10,000 hours (that’s a lot of occultations !). Bob Sandy stated that he can reach m = 10 stars with his PC-23C Supercircuits camera on his 6” telescope. David Dunham mentioned that experience has shown that shorter focal length telescopes will show fainter magnitude limits that longer focal length Schmidt-Cassegrains. This is due to the fact that there is more light falling on fewer pixels.   

Gene Lucas described an image intensified system he has been using with a C-14 telescope since 1985. It was used to broadcast live images of Halley’s Comet in 1986.  Gene had also used this system to view the Spica graze in June 1995. He had 17 observers with five of them using video. This event produced a very accurate limb profile.

Following a lunch break Bob Sandy explained some of the symbols used on graze profiles and how to read them, including his reduction of the June 1995 Spica graze. The graze elements were computed by Dr. Mitsuru Sôma of Japan. There were 48 observers on 5 expeditions from California, Arizona and New Mexico. A total of 209 timings were made. The expeditions were close to Temecula, CA; near Salton Sea, CA; Gila Bend, AZ; Almagordo, NM and Lincoln National Forest, NM. (One of the observers was Alan Hale of Comet Hale-Bopp fame). For the graze profiles Bob Sandy showed, not all of the observer’s timings could be plotted due the cluttering up of the diagram. He discussed several key timings in which the data clearly showed the size/shape of mountain peaks. Bob recommended that graze leaders reduce their profiles ASAP so that future observers can use their data at similar Watts angles. This can help avoid a “miss” and help maximize coverage. 

David Dunham then showed that using Hipparcos proper motion data, previous asteroid occultations could be re-reduced to update profiles. David then proceeded to show some slides of previous asteroid occultations including those from Isao Sato’s PhD thesis, “Asteroidal Occultation Observations From Japan.”  Those profiles shown were:

29 May, 1983 - 2 PALLAS profile showed some surface roughness. Had 131 observers with 13 on video.

1 CERES event from 1984- Lowell observatory profile. The data, when re-reduced with Hipparcos data showed the profiles matched quite well.


Other profiles with multiple chords shown included:

85 IO- 12 December 1995....................From Sky and Telescope          

27 EUTERPE - 9 October 1993..........From Sky and Telescope

1437 DIOMEDES-7 November 1997...From Japan

105 ARTEMIS-4 December 1997......Profile from Sky and Telescope Feb. 1999 page 106. There was a possible blink seen by one observer near the southern limit.

39 LAETITIA 21 March 1998- seen from 16 European sites. Profile in Sky and Telescope Feb. 1999 page 106.

25 PHOCAEA 13 May 1998- 8.94 mag star timed by Derald Nye with the Sun only 8( below the horizon!

248 LAMEIA-27 June 1998, observed from South Africa

75 EURYDIKE-3 April 1999. This event was clouded out over most of the New York area. Only Alan McRoberts of Sky and Tel. observed this event from his backyard through thin cirrus clouds.

123 HERMIONE-3 April 1999- Bad weather over Texas/Oklahoma, Florida fogged in. Only one observer in Vidalia, GA timed the occultation.

Dan Durda and Alan Stern from the Southwest Research Institute gave a presentation on  the Airborne Asteroid and Planetary Occultation observations project. With this observation program, it is hoped to provide diameters, masses, densities and albedos of asteroids. The observations are made aboard an F-18 Hornet jet operated by NASA’s Dryden and Edwards bases. This concept of airborne occultation observations has the following advantages: 1) an unobstructed overhead canopy. 2) The F-18 is a common aircraft - available worldwide. 3) Cost effective - several $1,000/hr operation cost versus the much higher cost of operating large airborne observatories like the KAO and SOFIA. 4) Range 420 miles between refueling.

The equipment used for the airborne flights includes a Xybiaon intensified CCD camera with video frame rates of 60 fps with a Nikon 85mm f1.4 lens. This setup can reach 10th-mag. stars with a 6.7( X 5.7( FOV.  A Sony 8mm camera is used as a backup. The monitor is a Citizen LCD. The primary recording is signaled off an onboard GPS navigation system. Test Flights 1-3 confirmed that the system worked as expected.

Test Flight 3 (a night flight) was on December 11, 1998. This flight happened to coincide with an occultation by 245 VERA. The system detected the target star easily but did not see the occultation due to a shift in the path. Current plans are to adapt this system to other jets such as the F-15/T-38’s. In the planning is to fly two planes in formation to obtain chords. Dan Durda showed some slides of the setup on the F-18 hornet and a video showing the amazing stability of the system from one of the test flights.

Following this talk the attendees took a break and posed outside Chamberlin Observatory for a group photo.    

President Dunham briefly described a popular B&W video camera that he and several IOTA members use - the Supercircuits PC-23C video camera. It is available from Supercircuits in Round Rock, Texas (, 1-800-335-9777). Price is about $79. Bob Sandy then showed the system he uses for occultation work: an approximately $250 Wal-Mart 9” TV/VCR combo with the PC-23C video camera. The camera has a built in microphone jack so that observers can make live comments during events. This is useful so critical information can be recorded about sky conditions, possible spurious events and other needed info to analyze the tapes afterwards. Sandy, who has been observing occultations since 1960, uses a Radio Shack SW radio and a cassette recorder as a backup. Richard Nugent then showed his compact Sharp 8mm camcorder model VL-E650U (price about $550) that has a built in 3” color LCD screen for viewing events as they are recorded. This 8mm camcorder also has direct cable feed audio and a built in speaker so the observer can hear WWV time signals as he sees the live video. This being a battery powered unit that fits in your hands, this makes a very portable lightweight system for traveling.   

The meeting was adjourned at about 4:30 PM.  Following this started informal  discussions. Some of the attendees watched an occultation smorgasbord video while others talked about their own occultation and astronomy research.  Following dinner, some attendees returned to the Chamberlin Observatory for some views of Mars and other objects through the 20” Clark refractor courtesy of Dr. Bob Stencel.

 Sunday, April 18, 1999

 The IOTA meeting continued at 10:00 AM at Denver’s Gates Planetarium. David Dunham showed a 9:15AM satellite photo showing a standing wave of cloudiness over Denver and the Front Range. In preparation for the Aldebaran graze later that evening, the weather situation would be monitored throughout the day.

Don Asquin, the Director of Gates Planetarium/IMAX theatre opened the meeting and welcomed IOTA members to the Denver Museum of Natural Science. He would keep the satellite web pages active on the office computers for monitoring the weather status through out the day. 

Sandy Bumgarner then described his ideas for a Remotely Operated Bright Object Telescope (ROBOT) and passed out an information sheet showing its proposed features and capabilities. The system would be designed with a narrow field,  minimum setup and tear down capability. The proposed large 20-30” f/2 system would be solely for occultation videos. A video camera would be placed at the normal location of the secondary mirror. The mount would be an Alt-Az with a jack type screw altitude and friction drive driven by a jack-type servo using precision sensors. Pointing would also be done by precision angle sensors. This proposed 12V system could potentially reach occultation stars to 15th  magnitude and would fit into a standard mini van.  Gene Lucas mentioned a few existing systems to simplify the construction of such a system. Interested parties in passing ideas around about this system can contact Sandy Bumgarner directly at       

Frank Anet from Los Angeles spoke on a video-audio software system that would display WWV audio signals as .wav files for timing purposes.  Such a system would provide accurate details on all parts of an occultation, including “light curves” during the rise and fall of light variations during an occultation. Such recordings could be downloaded to a computer system for frame by frame analysis.

David Dunham described the OCCULT program in it current form. OCCULT was written by David Herald originally in BASIC on a Commodore 64K computer, although now it is PC compatible.  It is a widely useful program to predict Lunar and Grazing occultations, occultation observations needing reduction to ILOC format, asteroidal occultations, solar and lunar eclipse predictions, and transits of Mercury and Venus. The program is currently downloadable by ftp from the IOTA website, where more details can be found.  Another program described by Dunham was GRAZEREG; it generates IOTA’s official graze predictions and was written by E. Riedel.

Rick Frankenberger ( mentioned a program by Fugawi that would plot lines on USGS topo maps.  This would be extremely useful for coordinating graze expeditions and save much time in locating and positioning observers.

Steve Bisque of Software Bisque briefly described The Sky software program version 4. It has the addition of the Hipparcos and Tycho catalogues in its database. Steve also described his own automated telescope system and how T-Point, a telescope slewing system works. Steve was planning on joining the Aldebaran graze effort later that evening.

Prior to the lunch break, the discussion among attendees centered on the Public outreach effort for the evening’s graze (media coverage, or lack of it) and previous experience with camcorder timings including satellite transmission processing delays, camcorder recordings, and their calibrating with TV/cable stations.  David Dunham showed predicted times and moonview charts of the Aldebaran occultation from cities across the USA. He said that although the January 26-27 Aldebaran occultation was seen by many well known astronomers, few of them advertised this event to the local public or made any timings. Dunham also showed moonview predictions for local Denver/ Cheyenne area in the hope that local residents with camcorders could record the occultation. But lack of publicity prevented that.

As an attempt for further public outreach on this event, David Dunham’s mentor student, Eric Schindhelm of Maryland, wrote an article about the May 21st Regulus occultation and its scientific importance in “High School Views”, a publication read by about 10,000 high school students in Howard County, Maryland. It is hoped that this timely article would foster astronomy, occultation, and other IOTA activities by students in the area.

Following lunch, David Dunham went over the graze plan for the evening Aldebaran event. Since the weather was still cloudy over Denver, plans were discussed about driving to alternate sites. The current plan was to meet at the Kiowa Feed store in Kiowa, Colorado at 7 PM. Contingency plans were also discussed.  

Additional discussion was made for the location of the year 2000 IOTA annual meeting. Dunham preferred to have it in Kansas City, where many key IOTA members live. Bob Sandy was quick to point out that these meetings should be in the path of major grazing events. 

With this, the meeting closed at 3:35 PM.

 P.S.  The skies over Kiowa, CO cleared after sunset. The Aldebaran graze was successful under clear skies. Details of the event will appear elsewhere.

IOTA's Annual Meetings

The International Occultation Timing Association is the primary scientific organization  that predicts, observes and analyses lunar and asteroid occultations and solar eclipses.  IOTA astronomers have organized teams of observers worldwide to travel to observe  grazing occultations of stars by the Moon, eclipses of stars by asteroids and solar eclipses since 1962.