Observation: Ganymede Shadow Transit of Jupiter

Ganymede   (Click for Larger Picture)

Ganymede (Click for Larger Picture)

I and several other members of the Northern Sydney Astronomical Society met tonight on a field location and were a little surprised by the clouds that gathered overhead as we set up our telescopes. The skies had been totally clear all day. It was now about 85% overcast and not looking promising but the clouds did eventually clear to give us some observing time.

Viewing conditions were not ideal but we did manage to observe some nebula and a few other objects. I was not having a good time with my telescope as the wind had pushed my scope over and caused some minor damage.

One of the other members of the society had his scope trained on Jupiter and when I looked at Jupiter through his scope , I asked what the little black dot was on the planet. We studied Jupiter and came to the conclusion that the little black spot must be coming from Ganymede, which is Jupiter’s largest moon with a diameter of 5262 km. Ganymede is actually larger than the smallest planet in our solar system, Mercury, which has a diameter of only 4879 km. Mercury is also beaten in size by Titan which is the largest moon of Saturn with a diameter of 5150 km.

On returning home, I confirmed that what we had seen tonight was indeed Ganymede’s Shadow Transit of Jupiter which ended at 8:31pm.

Due to the clouds returning and sky conditions beginning to deteriorate, we packed up our scopes at 9:30.  If the clouds had stayed away, we might have stayed and actually seen another moon, Io, which also began a shadow transit of Jupiter at 21:46.

A pity we did not see Io’s transit….. but the weather was deteriorating and seeing Ganymede’s transit was one of the highlights of the evening.

I have put together a diagram below showing what Ganymede’s  transit looked like when we saw it. It was diffacult to see at first as it was just a very small black dot shown on Jupiter ……. as seen below.

Ganymede Transit of Jupiter 16/10/2009

Ganymede Transit of Jupiter 16/10/2009

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~ by sydneystargazers on October 16, 2009.

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