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  Pluto System Occults UCAC 2603 9859

June 12th 2006,  16h 25min UTC

At the moment, not all graphs, maps and informations are available. But they will be presented soon.

General overview

The Pluto system will occult the star UCAC 2603 9859 (15mag) on June 12th, 2006 around 16h 25min UTC, as first pointed out by Dave Herald (WINOCCULT, DE405) and Jean Lecacheux in early March. A new prediction for this important occultation has been done by Bruno Sicardy, Observatoire d Paris/Meudon using DE413 and an improved ephemeris of P1 and P2. The main visibility areas of the occultation by Pluto itself will be New Zealand, Tasmania, southern Australia and Reunion.
Even more important, following the discovery of the recently discovered small satellites P2, an occultation of this small body will take place about 1000km north of Pluto's occultation track.

The scientific goals of an observation of this important occultation are:

  • For Pluto,
  • to determine the atmospheric static conditions (Temperature, Pressure etc.) and to compare it with data from past occultations, to get an idea of the development of Pluto's atmosphere during the loss of energy due to the increasing distance from the sun.
  • to determine winds in Pluto's atmosphere by a possible measurement of a central flash from Tasmania or New Zealand.
The results are of special interest to the New Horizons mission to Pluto, because possible smaller bodies and/or a ring system around Pluto may have a significant impact on the mission.

In order to observe the small satellite P2 by this occultation, a lot of stations is necessary. The approximate diameter of P2 is only around 100 km. So it will be a real challange. Everybody in the area of Central and Southern Australia, Tasmania but also on Reunion is encouraged to observe! IOTA-ES will try to coordinate together with other organizations as well the preparations and obervations for the event. Obervations by the team around Bruno Sicardy are planned in Tasmania and New Zealand.

The event carries the number P384.2 on the MIT list

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The occultation track

Bruno Sicardy calculated the following map for the occultation event:


B. Sicardy reports, that the above prediction is an update to older ones in the sense that they include the O-C offset

observed last year on Charon (ra:+0.022 de:-0.012). Otherwise there is no update for the star position, the position ist still based on observations by R. Behrend, ESO 1.2m telescope) .

Because of the earth's rotation, for Reunion's occultation by P2  there is a slightly other view for an occultation time of 16:07, which is presented in the prediction below:

P2 update

This prediction by B. Sicardy, Observatoire d' Paris-Meudon, is based on observations from La Silla's suisse 1.2m telescope on April 2nd 2006 and has been reported by Raoul Behrend. The red stars mark the positions of larger observatories in the area.

This image will be updated, as soon as new predictions are coming in.

Different groups have plans to observe this occultation, including Bruno Sicardy for the observatory Paris/Meudon. IOTA-ES will try to coordinate observations by amateurs and Professional astronomers in the described area, and may organize an own expedition. Contacts to observatories and interested amateurs in the area will be established.
In case of an own expedition, we are looking for cooperation partners in Australia and New Zealand, who can support such an expedition with logistics, transportation and instrumentation.

Because of the faintness of the star and the Pluto system, it is to be expected, that the minimum telescope size for observation will be around 25cm. Because of the very unfavorable position of the occulted star in the sky right now, there are no precise photometric measurements with IOC cameras right now. As soon as photometry is available, it will be presented here.

The track will be updated as soon as new predictions become available. Stay tuned!

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Details of the Pluto system

The following graph shows the Pluto system, as it looks at the time of occultation.

Calculated by Bruno Sicardy, Observatoire d Paris-Meudon. The red line is the projection of the star as seen from an observer in Hobart, Tasmania.

From Raymond Dusser a nice drawing, adopted from M. Buie has been sent in together with a good explanation for the situation of the system with the 4 bodies:


How the occultation looks from either Hobart or New Zealand (Mt. John), can be seen below. You also see the "miss" of Pluto itself from Reunion.


Here is the latest prediction for the P2 occultation, issued from B. Sicardy on the 28th of May. The asteriks show possible observing sites.

P2 occultation

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The Images with different cameras

Using a MINTRON 1/2 inch EXVIEW Chip camera with 48x integration time (equivalent to about 1 second) images of Pluto and the target star have been recorded with an 11 inch Schmidt Cassegrain telescope from Munich on the 3rd of May, 2006. No extra filter has been used. Pluto was only about 22 degrees high, therefore the airmass is pretty high. The focal length was about 900mm at 1/3 focal ratio. Because the site of the telescope was only 5 km south-east of the city center of Munich, background light was very high. Therefore no precise magnitudes can be given. It is expected, that the same quality of image can be reached in Tasmania/New Zealand with about 1/4th of the integration time.


Here is an image from the target star with the same conditions as above.


Here we have new images with the IOTA Occultation Camera (IOC), each with 4 seconds exposure time and 1800mm focal length.

Pluto with IOC

And here the target star, very faint, because of the high background due to the city lights from Munich (Only 5km away from the center of Munich and only 22 deg high.

From Jean Lecacheux, a 3' time 3' image of the target area including the target star is shown in the following image:

target field 3 times 3

Dave Gault from Australia got an interesting image recently from the target star with an 10 inch SCT telescope. He used the black and white version of the DSI camera from Meade with an exposure time of 1 second. You can see this fine image here . The image has been taken only 20 degrees away from the near full moon (about 20 degrees distance)! Therefore the situation is very similar to the real event on the 12th of June!

Photometry of Pluto and the target star

Photometry of Pluto and the target star with small telescopes from central Europe is very complicated, because Pluto has an maximal altitude of about 25 deg this year. The problems arise even more, if the telescope is in or near a big city (such as Munich!). A lot of extra haze and the city lights generate a big problem for precise photometry.

However, at high altitudes and far away from big cities at Pic du Midi, Jean Lecacheaux got the following BVRI photometry of Pluto and the star. The data are taken on the 11th of May, 2006 with the 1m telescope:

Pay attention: Pluto is variable during its 6.4 day rotation, so that the contrasts given below could change a little bit.
contrast = 100% * Star / (Pluto+Charon + Star)
Therefore, if the star is occulted, the measured intensity is expected to drop by the approrpiate value. In case of the I Band par example, the star signal is 45% of the sum of Pluto + Charon + star.
The contrast values have either been measured (for BVRI data) or estimated from catalogue values (K H J Bands)

Table of contrast for Pluto 384.2

Filter Band

contrast from

- - - - -
87 %
- - - - -
- - - - -
- - - -

RG 695: a long path filter with a cut off wavelength of 695 nm has been used in this case.

The weather conditions

Weather informations of the past can be found at different websites. You can see an overview of the global cloud coverage at the land cloud atlas at

Other important site is
where you can find the "Climates of the World"  giving a lot of informations at

A commercial german website with reasonable good informations can be found at

You can select the country and the city. Par Example, for Tasmania , you find the city of Hobart.
Then you get climatable with data such as max and min temperatures, rel. humidity, rainfall, number of days with rain and sunshine hours per day.

This may help to find out your weather for this important event. For commercial reasons, I will not copy directly the data to this website, you should follow the given links by yourself.

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Finding Charts

Pluto at the 12th of June, 2006

For the time of occultation (12th of June 2006) here you find finder charts with different field width. They were prepared using the XEPHEM program and the UCAC star catalogue. Some magnitudes are written to selected field stars for information.

Field size 5 armin
5 min

The map above shows a 5' times 5' field with the UCAC numbers and the magnitudes as given in the UCAC catalogue. The star in the center of the circle is the star to be occulted.

The same field with some coordinates overlayed from the DSS 2R  sky survey (red color range) can be found below. The only star, labeled on the right side, ist the star to be occulted, UCAC 26039859. The field of view is again 5´ times 5´. Pluto will approach from the left in retrograde motion, passing between the stars on the left side of the one to be occulted.

Field size 5 armin


Field size 2 deg
2 deg

Field size 50 deg
50 deg

With higher resolution, you can downlowd finder charts with different field sizes from the following table in postscript format:

5 arcmin
30 arcmin
2 degrees
5 degrees
15 degrees
50 degrees

Pluto in the next months

Finding charts for Pluto in the next 3 months will be added soon.
They will show the orbit of Pluto with tickmarcks every two days (except for the July map, there its every day) and labels every 10 days. Each label and tickmark has been set for 0h UTC. Postscript files you can download from the server as well. Charts have been prepared using the XEPHEM program and the UCAC catalogue. These charts are to facilitate your observations for equipment testing etc.

Here you can download the files in full resolution as postscript files, but please, it will take some more days to finish this....

April 2006
May 2006
June 2006

The lunar problem

As you can see from the finder chart with 50 degree field size, the near full moon will be only about 15 degrees away from Pluto. This is a very serious problem, what can ruin your observation, if you do not take special precautions. Even with large telescopes you may not be able to find  and image Pluto, if scattered light gets into the tube of your telescope. A long dew cap may be necessary to definitely avoid direct moon light on your entrance pupil or get into the tube/gitter cell.
You should test this in the upcoming months. Try to image a faint star of about 14th to 15th mag, about 15 degrees away from the moon, take a full moon night, if possible, or a very bright illuminated moon! Select the position angle relative to the moon to be about the same, as during the observing night of June 12th! And use a similar hour angle for your observation!

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For more informations and contacts to other groups, please contact myself:

Wolfgang Beisker
International Occultation Timing Association (IOTA-ES)
Research and Development


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