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Europa Shadow Transit 19 November 2012

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#1 Special Ed

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Posted 19 November 2012 - 01:37 PM

Hello,

I caught the tail end of this transit of Europa and its shadow. The shadow was quite prominent against the bright South Temperate Zone (STZ) but Europa could not be seen in front of the zone.

Europa was trailing its shadow by about 40 minutes and appeared when it reached the darkening just inside the limb. The seeing had improved considerably by then and the moon looked like a cream colored three dimensional orb. Once it cleared the limb, it reverted to appearing like a 2-D disk.

I did the sketch with a 2B and 6B pencil on copy paper. The contrast was not adjusted but I did flip the drawing digitally.

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#2 stray1

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Posted 19 November 2012 - 05:00 PM

Hi Mike!

Thank you very much for this excellent sketch! You have verified for me that it WAS Europa's shadow that I observed this AM :D It looks like you caught it shortly after I packed up and came inside.

Thanks again!

:grin:

-stray-

#3 frank5817

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Posted 19 November 2012 - 05:23 PM

Michael,

Great sketch. I am pleased you got your sketching fix for the weekend. With your larger scope at the observatory you really are picking up fine details.

Frank :)

#4 niteskystargazer

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Posted 19 November 2012 - 07:16 PM

Michael,

Good sketch of Jupiter & Europa Shadow :).

CS,KLU,

:thanx:,

Tom

#5 Asbytec

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Posted 19 November 2012 - 08:25 PM

I echo Frank, with seeing near 6/10, you are seeing Jupiter quite well. Last week we had seeing that rough, I could not make out any of those details (except in the better moments at around 7 or 8/10.) Less than that, forget it.

There is something magical about a moon on the limb. Not sure how to describe it.

#6 Special Ed

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Posted 19 November 2012 - 09:12 PM

Thanks to everyone. :)

Stray--glad you caught part of the shadow transit--they are important events to see for those new to Jupiter observing and *very* cool.

Frank, I have the whole week off--T-giving is deer season here in WV and an unofficial statewide holiday--so I hope to get more time under the stars if NOAA wills it.

Norme, I agree--a moon on the Jovian limb is special and worth the price of admission. Not sure how to explain the 3-D phenomenon but I've seen it enough times to know it's real.

#7 frank5817

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Posted 19 November 2012 - 09:34 PM

Michael,

That's great, I wish you clear skies and some 10 out of 10 nights. :bigshock:

Frank :)

#8 Andrev

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Posted 19 November 2012 - 10:36 PM

Michael.

Very nice sketch. Nice representation of the cloud's bands.

Andre.

#9 JimPie

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Posted 20 November 2012 - 01:02 AM

That's a really nice capture of the transit. Always exciting.

#10 Special Ed

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Posted 20 November 2012 - 07:57 AM

Andre, Jim--thank you. :)

Frank, if I could have some 10/10 seeing this week, I would indeed be thankful. :grin:

#11 azure1961p

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Posted 20 November 2012 - 08:13 AM

I caught the beginning of this when the shadow was just following of the cm. I like the dettails you captured. My favorite was the lighter toned streak in the neb. My night went to hell quick before I could put together a sketch. Yours is great though. Oddly and no image or sketch supports it but I found the zone neath the neb the brightest and most conspicuous. Light value visually. I now think it was an illusion created by the darker belts running parallel to it.

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#12 Asbytec

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Posted 20 November 2012 - 08:34 AM

Ah, Michael, this was the same CM! You captured that bay and darker concentration, too. Nice. Yea, those white features are really starting to pop.

Pete, to me the STrZ is whitest (some images show it as grey, though, go figure.) Starting to see the NTempZ as grey, the EZ as tawney with white features.

#13 Jef De Wit

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Posted 20 November 2012 - 09:39 AM

Nice catch :waytogo:

#14 wfj

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Posted 20 November 2012 - 05:26 PM

... The seeing had improved considerably by then and the moon looked like a cream colored three dimensional orb. Once it cleared the limb, it reverted to appearing like a 2-D disk...


Perhaps this is due to the line of sight specular reflection of Jupiter limb "light" illuminating Europa's limb on one side, while Europa's other side doesn't get the same contribution, being backed by a greater percentage of space?

One test of this hypothesis would be that decreasing aperture would yield a briefer period of the effect, due to lack of angular resolution necessary to perceive such.

The human eye is incredibly sensitive to "differential" effects, both in the subjective (time invariant cognitive) and perhaps other (time varying subconscious). The first case is like shading on a ball, the second is that our vision detect that a pattern is changing yet not in a catagorizable / "above threshold" way.

A lot of time with DSO's near the threshold, you know somethings there but can't quite perceive it.

Anyways, I've seen this effect quite a lot with Jupiter. Have often thought that because of Jupiter's surface patterns being so variable, specular variation in reflection might make it easiest to see here among any of the planets.

Thank you Ed for the observation and the nice sketch.

William.

#15 Special Ed

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Posted 20 November 2012 - 06:55 PM

Thanks, everyone! :)

Pete, I know how frustrating it is when the seeing starts out with promise and then tanks. I don't even expect good seeing anymore--I just look and hope (unless there is an obvious frontal disturbance). I assume you were talking about the North Tropical Zone being bright? It has appeared fairly bright but yellowish to me all this apparition until this observation. I could not see any yellow color--just a dull grayish-white.

Norme, I thought your Nov. 17th sketch looked familiar. It was the dark festoon base on the NEBn with the rift to the south as well as the bay in the SEB that made me wonder. Always nice to have one's observations confirmed--especially by another visual observer. :cool:

William, if I understand you correctly, the spherical appearance of the moon is caused by being backlit by Jupiter as well as front lit by the Sun?

As far as this phenomenon being a function of aperture, I have observed it many times with my 20cm SCT, too.

#16 Asbytec

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Posted 20 November 2012 - 07:36 PM

Always nice to have one's observations confirmed--especially by another visual observer. :cool:


That feeling goes both ways, Michael. I was pleased you noted the similarities and rushed right over to your sketch. Yea, it's nice. Jupiter is quite a show, and when GF looks at it an says, "Uh huh..." Well, we kind of rely on each other. :)

#17 wfj

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Posted 20 November 2012 - 07:55 PM

Thanks, everyone! :
...if I understand you correctly, the spherical appearance of the moon is caused by being backlit by Jupiter as well as front lit by the Sun?


No - uniform illumination of a sphere(Europa) by multiple light sources (Jupiter, Sun) - see: http://www.enginemon...llum/illum.html, specifically: Posted Image .

Notice the darkening on one side (away from Jupiter's center but towards limb - less accumulated illumination), the lightening on the other side (closer to Jupiter's center away from limb - more accumulated illumination).

It helps to make a model of the geometry of the Jupiter, Europa, Earth/Sun arrangement to see why this works.

As far as this phenomenon being a function of aperture, I have observed it many times with my 20cm SCT, too.


I think the effect should diminish with aperture in the same way you lose color/size discrimination of the Galilean moons - less than 4/5 inches.

I see the effect in 10" plus myself. Haven't tried 8" yet - my skies haven't been good this season. Can't see the effect in my 4" refractor.

#18 Special Ed

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Posted 21 November 2012 - 08:12 AM

William,

Thanks for the further explanation and the link. After re-reading your original post and the additional info you provided, I understand what you are saying. It helps to visualize the geometry. It's the limb darkening that makes a disk appear spherical and that's what I see.

I don't do planetary observations with my 4.25" reflector (the deep dish mirror can't support high magnification) so I don't know how small one can go and still see this effect.

#19 Tommy5

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Posted 21 November 2012 - 10:50 PM

very nice Jup sketch, shadow transits are way cool like your in Jupiter's air space watching stuff happen in real time, saw Jup tonight lots of bands but windy and rough seeing precluded any sketch, thanks for sharing.

#20 astronz59

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Posted 22 November 2012 - 05:03 PM

Luuuurverly sketch! I was planning to observe this apparition, but it was clouded out. Thanks for sharing! :refractor::rollgrin: :bow:

#21 Special Ed

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Posted 25 November 2012 - 09:46 PM

T5, Astronz--sorry to take so long to say thanks for your comments.

Tommy, like you I often look at Jupiter for a while and decide the seeing doen't justify a sketch--I've been lucky lately.

And Astronz, it's more often cloudy than not here (statistically 66% of the days are cloudy). Hope it's not that bad in NZ.






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