(IAAC) Upcoming Research Observing Opportunity

Observation Opportunity Toward Analysis of the Atmosphere of Io

It would seem that no one has ever predicted any mutual eclipses 
of the Four Great Moons of Jupiter.  Discovering this, I attacked 
this immensely complex problem in 1996.  After several months of 
calculations, computer processing, and cross-checking, I came up 
with a series of predictions.  A group of events will occur during 
1997, with the next such series late in 2002.

Quite a few occultations are predicted, most of which are partial 
events.  A lesser number of eclipses are predicted, 23 of which are 
total or annular. (of the 1997 series)

Of these, two are events where Io blocks the Sun's light from 
Europa.  These two events, predicted for 4/12 and 4/16, are 
unique in allowing potential analysis of any atmosphere Io may have.

A fraction of a second before totality, the only light which could 
get to Europa had to pass within a few miles of Io's surface, on 
its way from the Sun.  If Io has an atmosphere (sulfurous, perhaps?),
additional absorbtion lines should appear in the spectrum of light 
impinging on Europa's surface.  This spectrum could then be compared 
with a standard spectrum of the light reflected off Europa to 
discover these differences, which imply gases in Io's atmosphere.

If a rapid series of spectra were taken as totality approached, it 
may be possible to identify the vertical distribution of components 
of Io's atmosphere.

As mentioned above, there are only two of these opportunities available 
prior to Dec 2002.  The first, on Apr 12, will only be viewable from 
parts of Russia and the Mid-east (about 85řE long. to 50řE long.)  The 
time of this event is JD 2450551.4384.  The second event will 
only be viewable just before astronomical dawn along the 
west coast of the U.S. on Apr 16.  (time JD 2450554.9847)
In both cases, both moons are West of the planet, Io about 1.6 
radii away and Europa about 4.3 Jupiter radii from the center of 
the planet.

It is my hope that some of the equipment available in west coast 
observatories might be done with their night's work due to the 
impending dawn's light.  If so, please direct a telescope with a 
spectrograph at Europa.  The event is rather brief.  Totality is 
predicted at about 17 seconds, with the entire eclipse phenomenon 
being completed in about 4 minutes.  There is a slight chance that 
a 1% sliver of the North edge of Europa may not be eclipsed.  This 
should not materially affect the experiment described above.

The other 21 total or annular mutual eclipses involve various 
combinations of the four moons.  These occur later this spring and 
summer.  Several would allow similar analysis of the atmospheres 
of Ganymede and Callisto.  

If nothing else, it seems that it would be memorable to even just 
visually observe such a rare event.  A few historical references 
exist where an astronomer was observing Jupiter and one of its 
moons briefly 'blinked out', but no one has EVER observed a 
predicted example of it.

If the differential spectrum concept develops useful results, a 
careful study of Saturn's system would be appropriate to predict 
when Titan might eclipse one of the other moons, thereby disclosing 
its atmosphere's constitution.  In addition, rapid sequence spectra 
of Jupiter's moons being eclipsed by the planet might give upper 
atmosphere details of Jupiter.

A full list of the 450 partial and total occultations and eclipses 
of the 1997 series is available on request.

There are some really odd events in this series.  On May 2, Io will 
appear to be substantially East of Jupiter while Callisto is ever 
further West of the planet.  An annular event will occur where Io 
will eclipse Callisto.  During the annular 'totality', Callisto will 
go into Jupiter's shadow.  The combined shadow pattern should be 
REALLY peculiar looking!

Finally, regarding Io again, a significant partial eclipse is predicted 
for the morning of April 9, visible in the Mid-west and West coast of 
the United States.  The time is JD  2450547.8921, which is near      
astronomical dawn for the Midwest.  A sliver of the South edge of Europa 
should remain lit by the Sun, about 7% of Europa's diameter.  This 
should cause Europa to drop about 4 magnitudes in brightness for 
about 20 seconds.


Carl Johnson
BA Physics, University of Chicago

PO Box 93
Thornton,  IL  60476

E-mail    PastorCarl@aol.com