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Tuesday, 4 August 2009


BAA electronic bulletin No. 00430  

Jupiter will occult the bright star 45 Cap (HIP 107302) on the night
of 2009 July 03/04 (Mon/Tues).  The star is visual magnitude 6.0 and,
for European observers, will be the brightest star to be occulted by
Jupiter for the next 100 years.

For UK observers, the occultation disappearance will occur at around
2258 UT (2358 BST), and the reappearance at around 0051 UT (0151 BST).
Both events occur against Jupiter's southern limb.  Jupiter's
elevation/azimuth at these times will be around +16º/148º, and
+22º/176º respectively (based on central UK).  The predicted times
are based on the star's reaching the 1 bar level in Jupiter's
atmosphere.  However, the star will start varying in brightness as it
passes behind the upper levels of Jupiter's atmosphere before
the above disappearance time and after the reappearance time.  To
make up for this and varying positions within the UK, observers
should be ready to observe these events for at least a few minutes
before and after the predicted times.  The 96% sunlit moon will be
34º away.

Unfortunately, owing to the large magnitude contrast between the star
and Jupiter (mag -2.8), *visual* observers are unlikely to be able to
detect the actual moments of occultation or any 'scintillation'
through Jupiter's atmosphere; the star will just be seen disappearing
into the glare.  Limb darkening on the disappearance (W) side may
help counteract this slightly.  Also, since the star is of spectral
type A7 ('bluish'), a blue filter may help.

However, any observer possessing a narrow-band 'methane band' filter
will be in luck as these were designed specifically for events like
this.  A batch of these filters (central wavelength 891nm, FWHM 17nm,
80% transmission) was recently obtained by the International
Occultation Timing Association (IOTA).  Weather permitting,
occultation observers across Europe will be using these filters and
hoping to video record and accurately time the events.  Good quality
light curves from these recordings can help to improve the knowledge
about Jupiter's atmosphere.

For more detailed information, please click through the following
link and its subsidiary links:-

Apologies if this e-bulletin arrives at short notice, or too late.
The writer is just emerging from the severe side-effects of the
China (Eclipse) Syndrome!

Clear Skies,

Andrew Elliott

Assistant Director (Occultations)
Asteroids and Remote Planets Section


BAA electronic bulletins service.      E-mail:
Bulletin transmitted on  Sun Aug 2 19:19:04 BST 2009
(c) 2009 British Astronomical Association

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