From: LARRY KLAES (ljk4_at_msn.com)
Date: Fri Mar 09 2007 - 10:28:41 PST
>From: AstroAlert <AstroAlert_at_nl.clickability.com>
>Subject: AstroAlert Newsletter
>Date: Fri, 9 Mar 2007 09:20:10 -0800 (PST)
skyTonight.com AstroAlert Best
Pluto Occultation Ever Predicted for North America on March
18th This is an AstroAlert from Sky & Telescope.
2007 Sky &
Telescope. -->The best occultation of a star by Pluto ever predicted for
North America will occur between 10:40 and 11:00 Universal Time (UT) Sunday
morning, March 18th, in northern and possibly central Mexico, the western
and central USA, and southwestern Canada. The star is comparable in
brightness to Pluto, with mag. V = 14.9 and R = 14.1. Since the motion is
relatively slow, useful astrometric observations of the occultation might be
made with telescopes of 10-inch aperture or greater, especially with
integrating video cameras like the StellaCam II, and I think that the
signal-to-noise ratio might be good enough to measure Pluto's atmosphere
with telescopes of 16-inch aperture or greater with video (especially
integrating) observations, where the integrations might be done over 4, 8,
or even 16 frames.
It may be possible to make useful observations from where astronomical
twilight is just beginning, in Manitoba, Minnesota, Iowa, Missouri,
Arkansas, and Louisiana, and certainly west of there, where the sky will be
dark; east of those places, the twilight may be too bright, though
Wisconsin, Illinois, and Mississippi have a chance. Low altitude will hamper
observations in Washington State and southern British Columbia.
Target Star and Occultation Path
The star is UCAC2 25823784 at J2000 RA 17h 55m 05.70s, Dec -16° 28'
34.4", in northwestern Sagittarius about 2.5° north of M23 and
0.7° south-southwest of 6th-mag. SAO 160915 at J2000 RA 17h 56m 19.1s,
Dec. -15° 48' 45". A central occultation would last about 6 minutes.
Maps, detailed finder charts, observing tips, and much other information
about this event are on Bruno Sicardy's website at
http://www.lesia.obspm.fr/~sicardy/18_march_07/. Due to the great distance,
there's still a fair amount of uncertainty in where the actual path will be,
as can be seen from the different predictions portrayed on Sicardy's
website, but at least the uncertainty is relatively small compared to
Pluto's diameter so that observers throughout the "lower 48" US states and
northern Mexico have a very high chance for an occultation.
With the current information, though, the location of the central line can't
be predicted well enough to guarantee a "central flash" that will occur at
the center due to focusing by the atmosphere. Observations of the central
flash will be especially valuable for studying Pluto's atmosphere, so as
many observatories as possible are encouraged to try to record the event so
that some of them might record the central flash.
Reporting Your Observations
Let us know your plans to try to observe this occultation (size and location
of telescope that will be used, and recording method) to try to coordinate
coverage of the event, to try to prevent duplication of fixed- site chords
by mobile observers. Now that Pluto and the star are close enough together,
accurate astrometric observations with long focal-length telescopes may be
possible (especially after the lunar phase decreases enough) to refine the
prediction of the central line.
If you obtain any video or CCD images of the March 18th occultation by
Pluto, please send an account of your observations, including your
observing-site name, longitude, latitude, elevation above sea level, and how
these were determined; a description of the telescope used; the observing
conditions; the Universal Time range of the observations; the method of
recording the observations; and the names of those who participated in the
observations, to me at david.dunham_at_jhuapl.edu. I will forward your report
to the astronomers who will be performing the detailed analysis of the
observations to obtain information about Pluto's atmosphere. It would be
best if you could post your observations (.avi files preferred for video) on
a website and also include the URL in your report. This can be done later,
or the observations can be written to a CD and mailed to the astronomers who
will be analyzing the observations, with details of that to be distributed
to successful observers shortly after the event, and which will also be
posted on my website for the event at http://iota.jhuapl.edu/pluto.htm.
Please check the online version of this AstroAlert on Sky & Telescope's
website for possible minor updates:
Any major updates will be announced via subsequent AstroAlert messages. Good
luck, and clear skies!
David W. Dunham
Sky & Telescope
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Copyright 2007 Sky Publishing
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