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Old 06-05-2018, 09:41 AM
Tropo-Bob (Bob)
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Chance to see Europa in front of its shadow

Europa transits across Jupiter during the crucial hours of Opposition during the evening of May 9th. Might the aligning of Europa with its shadow make Europa any more visible during its transit?

The shadows ingress is at 21.21 EST. Europa's transits begins one minute later, so I assume that is just before the precise moment of Jupiter being in opposition. The alignment of Europa and its shadow changes during the transit. Europa's egress from the transit is at 23.31, whereas the shadow does not egress for another 5 minutes.

With this sensitive change in alignment during this pre to post opposition period, I am wondering if Europa may be seen against the background of its own shadow? My guess is that the shadow will not be seen in the first half of the transit, but later, the shadow may be partly offset, and thus may appear to the trailing edge of Europa. Will this make Europa easier to see? I don't know, but this chance alignment only occurs irregularly every few years (that is, one of Jupiter's moons being actually in transit at the time of opposition).

Therefore, I intend to take this rare chance to observe and see (clouds willing!)
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Old 06-05-2018, 10:46 AM
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tonybarry (Tony)
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Thanks Bob for the heads up.

Regards,
Tony Barry
WSAAG
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Old 06-05-2018, 11:02 AM
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OzEclipse (Joe Cali)
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Bob,

Jupiters orbit is inclined by a small amount 1-2 degrees to the Earth's orbital plane and Europa's orbit also inclined by a small amount to Jupiters plane. Unless Jupiter is passing through ascending or descending node right at opposition and Europa is doing the same, the shadow and planet are unlikely to be perfectly aligned. This is a very very low probability event.

Jupiters orbital inclination is very small so the shadow and planet should be very close and maybe overlapping but my guess is the shadow will be above or below Europa, not passing behind it.

Joe
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Old 06-05-2018, 12:37 PM
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Tinderboxsky (Steve)
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Interesting event Bob and well worth a look.
I am in country NSW enroute to the South Pacific Star Party with all my gear tightly packed away in our vehicle. If a good night I will unpack and have a look.
With Moon and shadow very close it is an opportunity to try different apertures to what is the smallest aperture one can observe Europa through it's transit.
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Old 07-05-2018, 07:37 AM
Tropo-Bob (Bob)
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Quote:
Originally Posted by OzEclipse View Post
Bob,

Jupiters orbit is inclined by a small amount 1-2 degrees to the Earth's orbital plane and Europa's orbit also inclined by a small amount to Jupiters plane. Unless Jupiter is passing through ascending or descending node right at opposition and Europa is doing the same, the shadow and planet are unlikely to be perfectly aligned. This is a very very low probability event.

Jupiters orbital inclination is very small so the shadow and planet should be very close and maybe overlapping but my guess is the shadow will be above or below Europa, not passing behind it.

Joe
Thanks Joe.

I tried this observation once before, about 30 years ago! On that occasion, I saw no shadow at all. However, I only looked briefly and did not follow up later in the transit.

Your remarks are interesting and unfortunately I had not considered the slight differences in the orbital plane angles. Nevertheless, I can only try and see how it turns out.

Quote:
Originally Posted by Tinderboxsky View Post
Interesting event Bob and well worth a look.
I am in country NSW enroute to the South Pacific Star Party with all my gear tightly packed away in our vehicle. If a good night I will unpack and have a look.
With Moon and shadow very close it is an opportunity to try different apertures to what is the smallest aperture one can observe Europa through it's transit.
Thanks Steve, your comments have added value to what may be attempted on the evening.
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Old 09-05-2018, 05:26 PM
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Hi Bob,
The GRS will also begin to transit around the same time. 21:37 AEST, that visibility time is from Sydney, so aprox. around then for the rest of eastern Australia. Three events in one, what an awesome show from the King!
W.A. gets there GRS transit at 19:37 WST.

Thanks for the heads up on the Europa transit event. I thought.... I wonder if I can get luckier with a GRS transit as well (us girls like to push limits and all and then blow me down!
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Old 10-05-2018, 09:18 PM
Multiverse (Grant)
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Hi Bob & Suzy,
I did actually manage last night (albeit not the best night) to see the GRS & also Europa transiting. Couldn't tell you much about any shadow of Europa as my scope is not that powerful, but both these sights were a first & certainly a treat for me.
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