Edition 12 of the Astronomy On-line Newspaper

Observations of Occultations

Dear Astronomy On-Line Steering Committee,

I just learned about the Astronomy On Line WWW Astronomy Event, perhaps a little too late, since the information says that it lasts until November 22nd.

I visited the interesting site at http://www.eso.org/astronomyonline, and it seems to me that occultations provide a nearly ideal project for this.

So I am submitting two proposals for it, one on asteroidal occultations and the other on lunar occultations of Aldebaran, and also one called "Observe Occultations of Stars by Asteroids, and of Aldebaran by the Moon", which is just a combination of the other two, in case it would be better to have only one.

If it's too late to post these as projects on Astronomy On-Line, as I suppose is the case, perhaps the combined proposal could be included in a last e-mailing of your Newsletter. I think that it would greatly benefit our program if we could reach in this way all of the e-mail addresses that you have collected.

Best regards,

David Dunham
International Occultation Timing Association
J.H.U. Applied Physics Lab.
11100 Johns Hopkins Rd.
Laurel, MD 20723
U.S.A.
Telephone +1-301-953-5609, fax +1-301-953-6556
E-mail: david.dunham@jhuapl.edu and dunham@erols.com

Observe Occultations of Stars by Asteroids, and of Aldebaran by the Moon

1. ASTEROIDAL OCCULTATIONS

The International Occultation Timing Association (IOTA) is trying to enlist as many observers as possible around the world to monitor the close approaches of asteroids to stars, and time their occultations when one occurs. The sizes and shapes of asteroids can be determined from timings of occultations of stars from two, or preferably many more, locations. A good example of a sky-plane plot showing observations of an asteroidal occultation of the unusual M-type asteroid 216 Kleopatra is shown on p. 73 of the January 1992 issue of Sky and Telescope, and is also on the Web at http://www.anomalies.com/iota/more/why.htm.

IOTA wants 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 observer who can find variable stars and obscure deep-sky objects can also locate asteroidal occultation 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 numbers 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 me.

Worldwide predictions are given at our Web site under "Upcoming Events" at URL http://www.anomalies.com/iota/splash.htm.

A list of observing stations is given at the bottom of that menu; we would like to add your site if it is not already there. Those with CCD's and astrometric reduction software could also help with last-minute astrometric updates for these events to help target observers to the actual occultation paths, which before such updates are quite uncertain; for more information on that, see the Astrometry item on the menu at the above site.

2. LUNAR OCCULTATIONS OF ALDEBARAN

A four-year series of lunar occultations of 1st-magnitude Aldebaran (Alpha Tauri), the brightest star that can be occulted by the Moon, has begun. There are two more occultations during 1996:

November 25 - visible from Scandivania, western Commonwealth of Independent States, Siberia, and Alaska

December 22-23 - visible from northeastern North America, northern Scandinavia, and western Russia.

There will be many more possibilities in 1997. Timings of these occultations are valuable for studies of the lunar profile and for certain astrometric studies. The diameter of the star can be determined from high- speed recordings of its occultation. More information about the occultations, including maps of the southern limits of the 1996 occultations and times predicted for North American cities, can be found under Aldebaran on the Web menu of the International Occultation Timing Association (IOTA) at http://www.sky.net/~robinson/iotandx.htm.

The site also includes much general information about observing and timing lunar total and grazing occultations, and in its archives section shows the results of reductions of some of the previous Aldebaran grazes observed during the last series almost twenty years ago. There is a link to the Aldebaran page of the TIRGO site in Italy; that has additional region-of-visibility maps and tables, and also offers to calculate local predictions. Information is also given in my article, "Lunar Occultation Highlights for 1996", on pages 76 - 79 of the January 1996 issue of Sky and Telescope.


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Last update: Nov 19, 1996