November 28th, 2008

Preparing the Varuna Event – Status Report, 2008 Nov 27, 22:45 U.T.


Steve Preston’s new prediction (Nov 25) is based on a recent star position and the position of (20000) Varuna derived from observations made at Pic du Midi, reduced by Marcelo Assafin et al.

Steve gave strong weighting to the Pic du Midi observations at his calculations.


Bruno Sicardy (Observatoire de Paris, LESIA) states that the Varuna event should be prepared and monitored for several reasons anyway:


– to get a feeling of SNR’s obtained by the various people interested in future events of this kind.


– to have a rehearsal, as many things can go wrong in this kind of time critical observations.


– for the larger telescopes, get a better astrometry when Varuna is very close to the UCAC candidate star. Probably a relative accuracy of 20 mas or better might be obtained. The obtained, accurate offset can then be stored for future monitoring on how Varuna’s offset behaves with time.


– who knows, the astrometry can still change…


At the moment we are searching for potential observers in the southern hemisphere (e.g. Brazil, Namibia, South Africa).


There is still hope to catch the shadow of Varuna…




November 26th, 2008

New Prediction Update for Varuna Occultation - Major Path Shift

Steve Preston has calculated a new prediction. Unfortunately the path is shifted to the south and don't cross the earth anymore.

If there is any additional information, I will post it here.


November 21st, 2008

Preparing the Varuna Event – Status Report, 2008 Nov 21, 21:30 U.T.

Raoul Behrend (Observatoire de Genève, Switzerland) reports at Nov 20:
„Bernard Trégon is actually using the 60cm telescope at Pic-du-Midi, France. He had taken a few hours ago some images from the Varuna & target area. Unfortunately, the sky got foggy and moon illuminated just before and during the first shoots.
Nevertheless, I could use one frame for the measurement the star’s position on 2008 11 20.196121 : 07 29 48.161 +25 40 07.68 using UCAC2 stars including proper motions and no other corrections. This position is to be taken with the „only indicative“ flag. Varuna is totally lost in the fog. More observations will be available in the coming nights.”

Later this day Dave Herald made a prediction according to the position measured by Bernard Trégon:
Map of Prediction

He comments:
“The main effect – 3 minutes later, with the path being slightly further north (over France). I think this astrometry confirms that the star position is ‚about right‘. The real uncertainty is the position of Varuna – and hopefully someone will succeed in getting a current position…”

Marcelo Assafin (Valongo Observatory, UFRJ, Brazil) want to perform an independent reduction with his astrometric software PRAIA.

Francois Colas (IMCCE, France) has taken some images at Pic du Midi:
“I just have done some images of Varuna this night at Pic du Midi. Unfortunately we still have the old CCD, so it noise, big pixels and small field… I hope it will be useful. I observe 6 hours to get a light curve.
The observational conditions are: 105 cm telescope F (with reducer) = 5.65 m Pixel size 23 x 23 microns so 0.84 “ on the sky Field : 5 x 4 arcmin.“

There is a discussion now how to incorporate any new astrometry. Whether that be by way of a simple offset, or by way of a new orbit computation.

More in the next days…


November 16th, 2008

Preparing the Varuna Event – Status Report, 2008 Nov 16, 20:00 U.T.

At the moment position data and data of proper motion of the target star 2UCAC 40846256 are compared from various catalogues.
Dave Herald from Canberrra, Australia, has made a table of Vizier catalogue information. See the text file at the end of this report.

His comments about this table:

„In particular, the nominal catalogue precision is not indicated, and there are data items present in some of these catalogues that are not displayed in this listing. Main thing to conclude, however, is that UCAC2, CMC14 and SDSS give consistent positions with the UCAC2 proper motions. The one area of concern: the position from USNO-A2 would suggest a proper motion in Dec that is about half the UCAC2 value, and the APM-North position (epoch ~1950, internal precision ~0.1″, fit to Tycho2 ~0.5″) would suggest a proper motion of the other sign – I would discount the APM position, as it is inconsistent with all the others.“ (Dave Herald)

Robert McNaught (Australian National University) was asked by Dave Herald whether he might be able to get some astrometry of Varuna in the next couple of weeks – particularly if the asteroid and star could be on the same image. Because of the faintness, Mr. McNaught will have trouble with a precision for a single measurement of better than 0.2″. He will try over several nights, to improve. He will also see if there is an opportunity with the 2.3 meter scope.

Eric Frappa ( asked Martine Castets & Bernard Tregon, the amateur astronomers using the T60cm from Pic du Midi Observatory between November 17 and 23, to make an attempt also with Varuna and target star in the same field. They agree to try in case of clear sky…

Stay tuned…

Varuna Target star

November 16th, 2008

Prediction for Varuna Event by Steve Preston

Steve Preston has added a prediction of the occultation by (20000) Varuna at his web page:

Go to:

November 15th, 2008

Possible Occultation by Trans-Neptunian Object VARUNA
at Dec. 7th 2008, 2h 10min UTC

Bruno Sicardy gave the information about an EMAIL from Jean Lecacheux,
concerning a possible occultation of a 14th magnitude star by VARUNA
on 7th of December, 2008 aroun 2h 10min UTC.

Hello all,

a mail from Jean Lecacheux pointing out a potential stellar
occultation by the Trans-Neptunian Object Varuna, nominally visible from
SW Europe (Spain, Portugal, Canaries) and N. Africa on Dec. 7 around 02:10

Uncertainties are large though (1″= 31000 km at Varuna, whose diameter
is ~900 km, corresponding to a mere 29 milliarcsec on the sky…).

So, widespread observations are advisable, as the event might be visible
anywhere from all Europe, middle east (Israel, Turkey, etc…), and lower
above horizon, from East USA coast, Canada, Caribes, Venezuela, Guyanas,
see map attached.

Note that the star is faintish (V=14.7) but the contrast is very high (V
Varuna = 20.2).

Before embarking in more specific plans, astrometric updates are most



———- Forwarded message ———-
Date: Sat, 1 Nov 2008 14:42:36 +0100 (CET)
To: Bruno Sicardy <>


En l’absence de prévision par les collègues de Rio des occultations par
VARUNA, j’ai cherché ce qui pourrait advenir cet hiver, et je „redécouvre“
le phénomène de la nuit du samedi 6 au dimanche 7 décembre, dèjà annoncé
par D.Denissenko il y a 4 ans.

L’étoile est malheureusement faible, mais vu la durée de 43 secondes, on
pourra se rattraper en intégrant une fraction de seconde, surtout si le
télescope n’est pas trop petit. L’étoile sera d’ailleurs haute dans le
ciel au méridien de l’Europe de l’ouest.
Les magnitudes sont : V ~ 14.7, R ~ 14.5 , I ~ 14.1, … K= 13.4 .
Le B-I de +1.2 et le V-K de +1.3 caractérisent une étoile plus blanche
que le Soleil (V-K= +1.5) ou que Varuna (B-I= +2.1).

J’essayerai de surveiller cela du Pic.

Il faudrait sans doute prévenir en divers sites d’Europe (incluant les
Canaries, la Turquie,…), ainsi que sur la côte est de l’Amérique du

Amitiés à tous.

As soon, as we have more detailed information, we will forward it to everybody in the community.

Stay tuned!


The preliminary occultation track is as follows:

Varuna Occultation