The sizes and shapes of asteroids can be determined from timings of occultations of stars from two, or preferably more, locations. A good example of a sky-plane plot showing observations of an asteroidal occultation of the asteroid 216 Kleopatra (an unusual M-type) is shown on p.73 of the January 1992 issue of Sky and Telescope and is reproduced here.
Nine observers timed the star disappearing and reappearing behind it. These timings yield nine lines, or chords, across Kleopatra's profile (Dashed lines indicate no occultation). Two chords with poor time records were shifted to fit the rest, and the gray shape was then sketched to fit all the chords. More of them would have better detailed Kleopatra's odd shape, particularly the apparent 25-km-high mountain. Kleopatra was moving 10.6 km per second across the line of sight to the star.
More Information
Basic information about the better events expected for North America during 1996 have been published in an article on pages 68-71 of the February issue of Sky and Telescope, which also includes finder charts for these events in the Celestial Calendar section each month for which there are events predicted. More detailed charts and paths, and update news, are given under upcoming occultation events accessible from the events page.
The International Occultation Timing Association (IOTA) was established to encourage and facilitate the observation of occultations and eclipses. IOTA membership benefits include: A subscription to Occultation Newsletter (ON), which gives news of meetings, predictions, software, observing techniques and equipment, and results for solar eclipses and lunar occultations as well as for asteroidal occultations. An annual ON Supplement includes detailed finder charts and information about the 50 best asteroidal occultations visible from North America; similar supplements are available for other parts of the world as well. Members also can receive lunar occultation predictions for their location, detailed grazing occultation predictions for paths that cross their region, and local circumstance (time and distance of closest approach, and alt. and az. of the Sun, Moon, and star) predictions for asteroidal appulses that produce occultations somewhere in the world (considering 200 to 300 of the best events per year) and occur above your horizon at night (and day for stars brighter than 6th mag.). New members receive a roster of observers (1993, so now a little out of date; we'll update it as soon as we can) and draft version of our observing manual. IOTA is a tax-exempt organization under sections 501(c)(3) and 509(a)(2) of the (USA) Internal Revenue Code, and is incorporated in the state of Texas.
The Occultation Newsletter is published approximately four times a year. It is also available separately to non-members.
The Dunhams maintain the occultation information line at 301-474-4945. Messages may also be left at that number.
You can reach David Dunam, the director of the ITOA by addressing, e-mailing, or phoning:
David W. Dunham, 23-376 Applied Physics Lab, John Hopkins Rd, Laurel, MD 20723.
Telephones :
| Office: | 240-228-5609 |
| IOTA occultation update line: | 301-474-4945 |
| Faxline - give David Dunham at the top, and Room 4-134, ext. 5609 | 240-228-1093 |
| Home | 301-474-4722 |
| email: | david_dunham@jhuapl.edu |
Telephones , , , , or send
Please send editorial matters to:
| Editor: Rex Easton |
| Internet: Editor@occultations.org |
Send new and renewal memberships and subscriptions, back issue requests, address changes, graze prediction requests, reimbursement requests, special requests, and other IOTA business, but not observation reports, to:
| Craig and Terri McManus |
| 2760 SW Jewell Ave |
| Topeka, KS 66611-1614 |
| U.S.A |
| Internet IOTA@inlandnet.net |
Occultation Newsletter is published by the International Occultation Timing Association.
President: |
David W. Dunham |
Executive Vice President: |
Paul Maley |
Executive Secretary: |
Richard Nugent |
| Secretary-Treasurer | Craig and Terri McManus |
| VP for Grazing Occultation Services | Mitsuru Soma |
| VP for Planetary Occ'n Services | Jan Manek |
| VP for Lunar Occultation Services | Rob Robinson |
| ON Editor: | Rex Easton |
| IOTA/European Section President: | Hans-Joachim Bode |
| IOTA/ES Secretary: | Eberhard Bredner |
| IOTA/ES Treasurer: | Alfons Gabel |
| IOTA/ES Research & Development: | Wolfgang Beisker |
| IOTA/ES Public Relations: | Eberhard Riedel |
Asteroids pass in front of stars as viewed from Earth at night from time to time, casting a moving shadow onto the surface of the Earth. The perpendicular cross-section of the shadow is the exact size of the asteroid and thus can be used to measure the shapes and sizes of the asteroid. The more observers of the event (occultation) the more accurate is the representation of the asteroid. Thus, the prediction of the location of the shadow paths across or near populated areas is critical to getting observers positioned along (across large arcs of the Earth's surface) and above and below the path to obtain different chords (and account for prediction errors). The image above crudely simulates what is happening between the star and asteroid with respect to earth.
IOTA is trying to identify and measure coordinates of all observatories from which these events might be observed, since more observed chords give better resolution of the asteroid's shape. Any observers who can find variable stars and obscure deep-sky objects can also locate asteroidal occultaton target stars and can contribute to this program. E-mail addresses of potential observers are useful, since E-mail is the most efficient means of notifying large num bers of observers about last-minute updates in the predictions; these events can be predicted most accurately when the objects are in the same CCD field of view usually only a day or so before the event. Although intensified video, photoelectric, and CCD observations are preferred, visual observations are also needed to get a dense enough set of observations to trace the asteroid's profile. Visual timings can be made with simple equipment such as tape recorders and camcorders (essentially used as tape recorders). If you, or someone you know, can contribute to this effort, please contact the IOTA, so you can be informed of last minute updates by e-mail when the update shows that the occultation might be visible in your region. These updates will also be posted on this site in the near future.
Observers from Europe and the British isles should join IOTA/ES, sending DM 40.-- to the account IOTA/ES; Bartold-Knaust Strasse 8; D-30459 Hannover; Germany; Postgiro Hannover 555 829 - 303; bank-code-number (Bankleitzahl) 250 100 30. IOTA/ES members receive the same benefits as IOTA members.
The addresses for IOTA/ES are:
| Eberhard Bredner | Hans-Joachim Bode |
| Ginsterweg 14 | Bartold-Knaust-Str. 8 |
| D-59229 Ahlen (Dolberg) | D-30459 Hannover |
| Germany | Germany |
| Phone | (49 or 0)-2388-3658 | (49 or 0)-511-424696 |
| Fax | (49 or 0)-2381-36770 | (49 or 0)-511-233112 |
For lunar occ'ns and eclipses: http://www.sky.net/~robinson/iotandx.htm
Edwin Goffin, IOTA and EAON, supplies the following information about the role of EAON.
The results - in the form of graphs - are distributed worldwide by IOTA to interested observers.
For Europe, this is done by EAON, the European Asteroidal Occultation Network. This is a small group of people in Belgium and France who make up a yearly observing programme based on my predictions, distributes them with the help of the Observatoire de Meudon, and collects and analyses observational results. The founder and driving force of EAON is my countryman :
Roland Boninsegna
Rue de Mariembourg 35
B-5670 Dourbes
Tel. : 32-60-399925
Note: Francis Delahaye (Bordeaux - France, address and email unknown at this time, will be replacing Roland Boninsegua.
IOTA annual membership dues, including Occultation Newsletter and supplements:
for U.S.A., Canada, and Mexico
$30.00
for all others
$35.00
Annual IOTA membership dues may be paid by check drawn on an American bank, money order, cash, or by charge to Visa or MasterCard. If you use Visa or MasterCard, include your account number, the expiration date, and your signature. ON subscription (1 year = 4 issues)
ON and supplements only:
for U.S.A., Canada, and Mexico
$20.00
for all others
$25.00
Single issues are 1/4 of the price shown. Although they are available to IOTA members without charge, non-members must pay for these items:
Local circumstance (asteroidal appulse) predictions $1.00
Graze limit and profile predictions (per graze)
$1.50
Papers explaining the use of the predictions
$5.00
Asteroidal occultation supplements will be available at extra cost:
for South America via Orlando A. Naranjo (Apartado 700; Merida 5101-A; Venezuela),
for Europe via Roland Boninsegna (Rue de Mariembourg, 33; B-6381 DOURBES; Belgium) or IOTA/ES (see above),
for southern Africa via M. D. Overbeek (Box 212; Edenvale 1610; Republic of South Africa),
for Australia and New Zealand via Graham Blow (P.O. Box 2241; Wellington, New Zealand), and
for Japan via Toshio Hirose (1-13 Shimomaruko 1-chome; Ota-ku, Tokyo 146, Japan).
Supplements for all other areas will be available from Jim Stamm (11781 N. Joi Drive; Tucson, AZ 85737; U.S.A.) for $2.50.
An Idea for Clubs
One individual could join IOTA as a club, for just $30, then share the predictions with other members in the club. Any members living far from the Club location might want a separate membership to get detailed predictions for their site, and maybe one or two might want to subscribe to our Occultation Newsletter separately for $20. Or someone might buy the OCCULT program and generate lunar occultation predictions for other sites around the county.