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Shadow transit of Io on Jupiter August 20th

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#1 Dee


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Posted 21 August 2009 - 08:11 AM

Around about a quarter past eleven in the pm, I opened my front door to see if Jupiter or anything was visible. Nice surprise, the sky was clear. Debated with myself if I should carry out the heavy LX90 or take a peak with my 8 inch DOB. Hmmmm …………. What to do? Figured I would check the seeing with the dob, it is just easier to move out of my study.

Oh brill !!! , some banding, enough to observe, longer seconds of clarity than I had noticed on previous occasions. A dark dot was very obvious in the equatorial region, not being a planetary observer the names of the banding layers do not freely come to mind. This was a sketching opportunity I never had before. Hmmmmmmmmmmm……………….. What to do? Will I set up the LX 90 as I was curious what it would offer me or stick to the scope I had in the moment?

Checked out observing software to see which Jovian moon it was.
Thinking that those pesky clouds were most likely going to descend any moment I opted to sketch what I had in view and not waste time setting up another scope. Maybe I could get a comparison sketch later if the weather held. My sketch pad had three 80 mm circles from a moon drawing project that had not see the dark of night for months due to cloud. That will have to do I reckoned, need to get something on paper fast.

22:40 UT Jupiter 19 degrees
200 mm / 8mm TVP eyepiece / FL 1200 mm /150 X to my eye /no filters / same info for all sketches.

In my view Jupiter was only approx 10 mm in diameter, not much point in drawing something so
small in the same scale as I am viewing it, up scaling is the only way to go about this.
So I sketched the planet to fill the full 80 mm circles (even though Jupiter is not a circle) and observed as much detail as I could.
The seeing was about 2/3 and up and down on either side of 3 for brief seconds and milliseconds
during the course of the first sketch.

23:20 UT Jupiter 20 degrees, getting windy, haze from time to time.
WOW !!! The Jovian satellite Io was galloping along, in its apparent motion east to west.
The shadow of the satellite was very clearly round and dark against the paler bright zone.
The north and south polar areas of the planet offered very little detail to me.
The bands that appeared white on the planet were very contrasting with the other darker bands.
Within the darker bands I noticed some variations in tone and with the constantly changing seeing I also noticed variations in structure as well, but not enough to sketch detail as I would have liked. The scope shaking from time to time in the wind did nothing to help.

23:40 UT Jupiter 21 degrees the shadow is moving closer toward the preceding limb of the giant planet. A short while later I began to notice that Jupiter seemed to be developing a dint in its limb visually speaking. I did not take note of that time exactly as I did not want to take my eye of the ball, literally.

(Mental note to self, record fast moving events by voice in the phone to have a date and time record, or have giant illuminous watch within eye flick distance, or both)

23:45 UT give or take a few minutes I observed the shadow changing shape, becoming crescent shaped as it grew closer and closer to the limb. I realized that the shadow was in effect showing me the limb the total disc of Io !!! Planetary observers correct me if I am wrong on this observation.

Jupiter had developed a pimple on its otherwise unblemished curving limb by 23:45 UT
At 23:54 UT Io had cleared the Jovian disc and was clearly visible all by itself in space.

My last observation was at 00:01 UT as Io had moved away by at least it own diameter again from the preceding planetary limb. Hazy and more windy then, end of story.


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#2 Dee


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Posted 21 August 2009 - 08:12 AM

Close up of last sketch


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#3 frank5817



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Posted 21 August 2009 - 10:02 AM

Hi Dee,

Delightful! It was exciting to read your running narrative and look at your sketching sequence. You chose wisely to observe and sketch. Well done! :bow: :flower: :flower: :bow: :rainbow:

Frank :)

#4 kraterkid


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Posted 21 August 2009 - 10:12 AM

A delightful report and excellent sketch sequence Dee! :flower: :jump: :flower: The emergence of Io you recorded reminds me of a time I was observing Jupiter and one of the moons popped out of the limb. The first impression I had was that I was witnessing a comet impacting with Jupiter! Then the moon cleared the disk of Jupiter and I realized I would not be the next Anthony Wesley! :lol:

#5 CarlosEH



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Posted 21 August 2009 - 02:53 PM


A wonderful report and set of observations of Io transiting across Jupiter. Observing transits of the Galilean satellites is exciting. Thank you for sharing them with us all.

Rich- I know how excited (and disappointed) you must have been with your "discovery." With all of the excitement about the Wesley Comet Impact Scar (WCIS) it is easy to understand why observing a back mark over Jupiter would make anyone think it is a cometary impact. It is still exciting to observe Galilean satellite transits.


#6 JayinUT


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Posted 21 August 2009 - 03:40 PM


An outstanding report and great sketches. Our local club's monthly meeting was on Tuesday and I couldn't go (Tuesday's are bad) and then they went out to the observing complex and observed transits and other items regarding Jupiter and its Galilean moons.

Your observation and one posted by the club's treasurer has made me regret not going late to the meeting and then following up with the observation of Jupiter and its moons.

#7 Tommy5



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Posted 21 August 2009 - 07:16 PM

Very nice sketches and exciting narrative of te Io transit these events are really cool to watch in real time, thanks for posting.

#8 JimPie


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Posted 22 August 2009 - 11:40 PM

Very nice observation sketches and detailed report.

#9 Dee


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Posted 23 August 2009 - 10:04 AM

Thanks to all for the very interesting comments on my transit sketches. I never gave much thought or time to transits but it was actually very exciting to watch and felt very special to draw.

It is truly amazing to observe objects doing what they do millions of miles away in space. It can be extraordinary what one can see from the front of ones house given a bit of luck , a little weather window.


#10 Special Ed

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Posted 23 August 2009 - 10:51 AM


An excellent set of observations and sketches. You mentioned in your notes how fast things were moving. That is the special challenge of observing Jupiter. In the 80 minutes of your observation, Jupiter rotated ~43° of longitude as Io sped halfway across the disk to emerge on the preceding limb. One has to pedal pretty hard to keep up. :p :)

Io can be very hard to detect against the Jovian disk, but I think you saw the change that happens visually as it nears the darker limb. In my experience, it almost always becomes observable then and even appears three dimensional to my eye. :cool:

#11 Dee


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Posted 23 August 2009 - 11:34 AM

Thank you for that important information re Jupiter rotation et cetra . I am not a planetary observer really and it is great to have this kind of input to fill in what I saw with my eyes.

Yes I did think I saw Io become Io and not a shadow of Io for a few brief moments. It may have just been an illusion or maybe it was real , tiny Io against the gas giant .

I think that is where sketching becomes such a valuable tool in learning . Sketch exactly what you see when you see it , and learn something from the experience .

Thanks again


#12 Jeff Young

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Posted 24 August 2009 - 01:27 PM

Great report, Deirdre!

I watched that one myself, but didn't get to see either entry or exit. Still, the middle bits were nice.

-- Jeff.

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