Alert Notice 464: Observers requested for Jovian Extinction Events (JEE2012)

July 5, 2012:  Scotty Degenhardt (Santa Fe, NM), a pioneer in the use of video for timing eclipses of solar system and stellar objects and a research member of the International Occultation Timing Association (IOTA), has informed the AAVSO of a research project he and colleagues are working on: modeling the Jovian dust field, moon atmospheres, and Io’s Torus through Jovian Extinction Events (JEE). He has invited AAVSO observers to participate by observing these Jovian extinction events and reporting their observations.

Regarding the possibility of AAVSO participation, Scotty writes: "I really look forward to the quality data that I know AAVSO provides. It will be quite the gemstone in the data set. FYI, I will be making a major presentation at SAS next year, so the work will for sure be featured there. We are planning on a major paper in Icarus as well, but we will just have to see how that pans out..."

Regarding the JEE project, he writes: "The next Jovian Mutual Event season (JME) is still almost two years away. But the interaction of the Jovian moons is upon us. In July and August there are multiple opportunities to record dimmings of Jovian moons via extinction of their light by the atmospheres of other moons and/or by the dust and gas material in the Torus of Io. The recently launched space probe Juno is speeding on its way to Jupiter to arrive in about 1400 days and their Director of the Pro/Am collaborative has recently expressed interest in collaborating with the JEE Project to see if any of our light curve data can give them additional insight into distribution of material in the Jovian System. (The Juno mission is described at

"Europa's atmosphere is documented to extend out to about 25 Europa radii from its surface. There will be numerous conjunctions, or close misses of Europa with Io and Ganymede over the next several months. These conjunctions do not involve occultations or JMEs. This means with the right magnification the two moons will remain separate light sources and not merge so that one can do photometry on each moon individually. these eliminate the problems of merging intensities (although when dealt with properly, merging intensities are not really a problem). Our previous study of JMEs and JEEs have shown that the source of dimming in these events is the moon that is behind the moon possessing a known tenuous atmosphere. The upcoming conjunction JEEs provide the best opportunity to document this extinction phenomenon and give rise to the possibility of inverting the light curve to produce a 3D model of the dust and gasses in the Jovian system.

"Out at the tips of the Torus of Io the material in this torus is collimated to our line of sight from earth so that when Io is behind the tips it is experiencing the extinction from a 200 Io radii column of dust and gas. We have made past observations showing the dimming from this amount of material is detectable in amateur scopes.

"JEE2012 is a great opportunity for amateur and professional astronomers to work together to accomplish something no one thought was possible. That is to actually detect and measure the tenuous atmospheres surrounding some of the moons of Jupiter as well as this same material that is captured in a torus ring around Jupiter, called the Torus of Io. The most exciting aspect of this project is that since the moons of Jupiter are bright compared to most astronomical endeavors, the JEE work can be done in the smallest of telescopes, putting the ability to accomplish a real scientific measurement in virtually anybody’s hands. We have documented measurements of Io’s atmosphere in a small 80mm finderscope. Thus even the amateur astronomer with the simplest equipment can perform some of the same measurements that our space probes have done flying out to Jupiter, and at a significant[ly small] fraction of the cost.

"A complete current prediction kit through Aug 2102 is available here:

"A summary table of upcoming events is here:

"A FAQ file describing the JEE2012 Program is here:

"It is important to note that we have developed a better prediction method which gives one a predicted light curve so one has a basis to know when and how long to observe. It is also important to notice that many of the upcoming events are 6 to 10 hours long and Jupiter is not currently visible for that long in any one location. So it will be important to get as many observations as possible from different locations in order to make a complete light curve."

B, V, and R observations are preferred, if possible; spectroscopy is also requested. Details of the observation procedure are given in the prediction kit, as are individual ephemerides for each extinction event. Once you have obtained data, please contact Scotty Degenhardt <> regarding data reduction.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.


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