Electronic Telegram No. 3138
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


POSSIBLE OCCULTATION BY PLUTO ON 2012 JUNE 14 UT
     Leslie Young, Southwest Research Institute, Boulder, reports that a
possible occultation by Pluto will occur at low altitude for observers in the
eastern United States and Canada on June 14.14 UT of a star of magnitude 13.8
(UCAC bandpass 579-642 nm) that is located at R.A. = 18h35m48s.688, Decl. =
-19d17'43".64 (equinox 2000.0).  Topocentric predictions for the midtime
depend on the combination of Pluto and star positions used, and vary by about
50 seconds for any location.  The midtime also depends on the location,
affecting the midtime by about 1 minute over the portion of visibility.
Adding uncertainty for Pluto's extended atmosphere and the chance of
systematic errors in the star's right ascension, the recommended observing time
spans 03h20m to 03h37m UT.  Any location near the entire east coast of North
America has a good chance of being in the shadow.  Pluto only subtends 0.1
arcsec, so small errors in the star position and Pluto ephemeris can move the
predicted shadow path substantially.  Predictions tend to be good to about 500
miles, barring systematic errors.  Multiple chords are critical for
reconstructing, after the fact, the geometry of Pluto's passage.  A mix of
central and more-grazing chords are most useful for most tightly constraining
the geometric solution.  Pluto is very low and rising (e.g., about 20 deg
at Boston, Philadelphia, amd Baltimore).  Details are given at website URL
http://wiki.boulder.swri.edu/mediawiki/index.php/2012-06-14_Pluto_occultation;
see also http://occult.mit.edu/research/occultations/Pluto/P20120614/ and
http://www.lesia.obspm.fr/perso/braga-ribas/campaigns/#June.  Data or reduced
lightcurves will be assembled by Young (email:  layoung@boulder.swri.edu).


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2012 CBAT
2012 June 13                     (CBET 3138)              Daniel W. E. Green