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Old 25-07-2015, 08:56 PM
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Tinderboxsky (Steve)
I can see clearly now ...

Tinderboxsky is offline
Join Date: Feb 2012
Location: Tinderbox TAS
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Jupiter's mutual moons events observation report

Well, the 6 yearly cycle of mutual events of Jupiter’s Moons has come to an end. We will need to wait another six years for the next cycle.
This cycle I set out to observe as many of the events as I could. I find these types of events interesting as one can observe actual motion in the night sky as opposed to the very static views of most observations.
There were just over 80 observable events listed in Astronomy 2015 Australia. I set out to see as many as possible without being too obsessive about it. However the weather conspired to hide many of them from me, then there were personal and family commitments that got in the way and I was not too keen on chasing the events in the early hours of the morning.
Still, I managed to nab 10 of the events. So here is a brief summary:

29th Dec ’14: Occultation of Io by Ganymede. Despite poor transparency, 113X proved best to view events. The two moons were observed to converge into one and then diverge close to the planetary disc. Difficult to see any dimming given the glare from Jupiter. Io's shadow was on the planetary disc and close to egress as the two moons diverged immediately after occultation. Shortly afterwards, Ganymede's shadow ingressed and at this point Io's shadow was close to commencing egress.
Cloud worsened preventing the subsequent events - occultation of Europa by Jupiter followed by transit of both moons. 140mm refractor.

7th Jan ’15: concurrent Io and Europa moon and shadow transits. A near full moon only 20deg away and low 18deg elevation of Jupiter made the observations a challenge. Both shadows were visible, becoming very sharp in moments of good seeing. Both transiting moon discs visible when near edge of the planetary disk in fleeting moments of best seeing. 140mm refractor.

18th Jan ’15: Partial eclipse of Ganymede by Europa. Dimming of Ganymede over the 42 minute period of the eclipse was clearly visible. Ganymede appeared to be just below the brightness of Europa at the mid point of the eclipse. 140mm refractor.

19th Jan ’15: Occultation of Io by Ganymede. Approach to occultation clearly visible but increasing wind made it difficult to resolve last stages of close approach and separation. 140mm refractor.

9th Feb ’15: Occultation of Europa by Ganymede. Occultation occurred very close to planetary disc. Approach, occultation and separation clearly visible. Expected diming not seen due to poor observing conditions, brightness of planetary disc and probably insufficient aperture. 85mm refractor.

15th Mar ’15: partial eclipse of Io by Europa and concurrent Calisto shadow transit. Thin high cloud made it difficult to see the projected 60% of normal brightness for the partial eclipse. Some dimming was just noticeable. Calisto’s shadow on Jupiter’s disc was a fine sight. Missed earlier occultation of Io by Europa due to too much daylight in early evening. 140mm refractor.

21st Mar ’15: Partial eclipse of Ganymede by Io. 50% partial eclipse: only slightest diming of Ganymede visible. This observation was made during the Ben Lomond star Party at nearly 4000 feet. The benefits of higher altitude were cancelled out by a night of moist air and fleeting high cloud bands. 140mm refractor.

28th March ’15: Occultation of Ganymede by by Io. This was only a 30% occultation but was fortunate to have good seeing and transparency. Separation see seen right up to approx 1.5 mins of expected initial contact, then pronounced egg shape during occultation and then separation seen approx 1 min after expected final contact. Io's path was just above the centreline of the orbital path of Ganymede. 140mm refractor.

11th June ’15: Concurrent Io and Ganymede moon and shadow transits and egress. Poor seeing and low elevation made observations very difficult. Shadow transits just visible. Io not seen until 8 minutes after expected egress. Ganymede not seen until 10 minutes after expected egress with elevation very low by then. Ganymede’s shadow egress occurred below the horizon and not seen. 140mm refractor.

15th Jun ’15: Eclipse of Europa by Io. Low elevation and heavy cloud cleared 5 mins before event but difficult viewing through fine cloud. Europa blinked out for approx 2 mins. 85mm refractor.


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