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Titan: is this diffraction or Einstein?

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#1 azure1961p

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Posted 07 May 2013 - 09:07 PM

Below is a link a lot of people have seen but it has something I haven't seen addressed and its got me flabbergasted. Simply, its a vid of Titan occulting a binary and even though the stars are buried well behind Titans FAT disc, if you look close you can see the "atmosphere" of Titan looping an image of each star as it passes by until it reemergence on the other side. One star flys over Titans 12 oock limb, the other guys below the 6 o'clock limb.

In each case the star is hopelessly buried behind this moon to even hope to begin to ever see it. Its not near Titans limb edge- its buried well behind it.

But we still see it looping AROUND Titan as if skirting its atmosphere.

I can only come up with two possibilities....

1. Its an effect of diffraction I have no clue about
2. Titan is LENSING the star gravitationally so it never truly disappears and is lensed along its circular limb.

I'm not ruling out 2. But I didn't think Titan would have enough mass to pull this off.

Here's the link:

http://youtu.be/7Pv8kBRIXAo

Pete

#2 David Knisely

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Posted 07 May 2013 - 09:58 PM

It is just standard light refraction due to the dense atmosphere of Titan (surface pressure is about 1.45 times that of Earth). The Earth's atmosphere bends the light of the sun by about half a degree as the sun is approaching sunset making sunset appear slightly later than it would without the atmosphere, so it is a well-known phenomenon. Titan subtends only about 0.8 arc seconds at mean opposition distance from Earth. Thus, the angle of bending for a distant star going behind the limb of Titan is pretty small, requiring only modest atmospheric refraction effect. Clear skies to you.

#3 Asbytec

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Posted 07 May 2013 - 10:33 PM

I think David is correct, Titan is hardly massive enough to noticebaly lens star light. The Sun does, and that was measured. But it's pretty small amount, Titan would be very small - so small, I doubt it can be captured like that.

#4 Rich (RLTYS)

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Posted 08 May 2013 - 05:15 AM

Most interesting. :question:

Rich (RLTYS)

#5 azure1961p

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Posted 08 May 2013 - 06:20 AM

If go with refraction too. That's seems the most plausible. A gravitational lensing takes awesome mass so I was never easy on that notion. Even for refraction though - that's a heck of a lot of bending considering how far behind the limb the stars get. I don't think astronomers have ever imaged anything so odd on another celestial body - or what lay behind it.

I'm guessing if the star was completely occulted dead center to Titan the starlight would form a ring all the way around it - momentarily anyway.

Pete
PS: I'd feel better about my post if in the YouTube vid the explanation was not given in the description! Oh well.

#6 Rick Woods

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Posted 08 May 2013 - 12:48 PM

I'm guessing if the star was completely occulted dead center to Titan the starlight would form a ring all the way around it - momentarily anyway.


Pete,

Not quite. This actually occurred on July 3, 1989, and was observed and recorded. When the star (28 Sag, m5.5) hit dead center behind Titan (as viewed from Paris), there was a central flash on the disk lasting about 5 seconds, as though the star were being see right through Titan. The atmosphere of Titan refracted the light all the way around. Evidently, a ring should have been formed if Titan's atmosphere were perfectly uniform, but it's not. This gave scientists a lot of valuable info on wind patterns on Titan, and was useful in planning the Huygens mission.
(Source: "Titan Unveiled", Lorenz & Mitton, pp. 53-54; a very interesting book!)

#7 orion61

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Posted 08 May 2013 - 01:17 PM

What was that taken through?

#8 azure1961p

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Posted 08 May 2013 - 02:06 PM

The 200" Hale if you can believe it. Adaptive optics is really at work here - hence the wildly high res.

Pete

#9 Asbytec

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Posted 08 May 2013 - 03:04 PM

The 200" Hale if you can believe it. Adaptive optics is really at work here - hence the wildly high res.

Pete


Ya, if it weren't for adaptive optics, well there goes everything I ever thought about aperture and seeing. :)

Hey, I observed this occultation Rick mentioned.

So, it's neither diffraction or Einstein, eh?

#10 Rick Woods

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Posted 08 May 2013 - 03:21 PM

The 200" Hale if you can believe it. Adaptive optics is really at work here - hence the wildly high res.


No, it was at Meudon. They got the flash for 5 seconds; it was shorter elsewhere. Not sure that occultation was even visible in the USA.

The 200" with its new AO system was used for for an occultation of a mag 12.4 star on 12/20/2001. No flash on this one, Titan wasn't dead center for anyone.

#11 azure1961p

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Posted 08 May 2013 - 03:28 PM

Ok just basing it off the YouTube blurb in the vid.

Pete

#12 azure1961p

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Posted 08 May 2013 - 03:30 PM

Okay I reread it - December 20, all American astronomers, hale telescope with adaptive optics. 2001 was the year.

Thanks,

Pete

#13 Rick Woods

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Posted 08 May 2013 - 05:09 PM

My reference said the "central flash" occurring with such a bright star only happens about every million years; and they were lucky enough to catch it!
Things do go right sometimes! :D

#14 Rick Woods

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Posted 08 May 2013 - 05:13 PM

Hey, I observed this occultation Rick mentioned.


Norme,

Really? The one in 1989? Were you in Europe at the time? Did you see the flash? The light curves I saw made it look pretty faint; I think you'd need a good sized scope (10"-12"?) to see it; especially if you weren't looking for it.

#15 Asbytec

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Posted 08 May 2013 - 07:00 PM

Rick, maybe I was wrong. But about that time a star in Sag went behind the rings. I think it was 28 Sag. No, I did not see it eclipse Titan. Sorry for not being clear. I believe it was the same star, same event...but eclipsed by the rings.

#16 azure1961p

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Posted 08 May 2013 - 07:03 PM

Oh thaaattttt - I missed that!!! Twice infact as I recall another time in the 70s - clouded out. This is one of those huge things I regret missing.

Norme - full us in please!



Pete

#17 DesertRat

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Posted 08 May 2013 - 09:24 PM

The above referenced YT video of the binary occultation by Titan was done with adaptive optics on the 200" Hale. It was also observed at several other observatories in the western hemishpere.

For a good techinical reference on how it was done see the paper:
Adaptive optics imaging of a stellar occultation by Titan

Glenn

#18 David Gray

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Posted 09 May 2013 - 02:48 AM

No, it was at Meudon. They got the flash for 5 seconds; it was shorter elsewhere. Not sure that occultation was even visible in the USA.


28 Sgr Titan Occultation: I saw this (tho’ not the flash) when on nightshift at the bakery (UK), but only had the 12x65s; resting them on the horizontal security bars of the locker room window.

I somewhat abused my position as shift foreman by re-arranging the production schedule so I could time the break to coincide with the critical time of the event! Thus memorably conducted the observation to the accompaniment of the guys, in the adjacent canteen, getting heated over their card game!

Only binos; but as we say here ”Better than nowt [nothing]”!

Seems a fair few got the flash as alluded to by Andy Hollis in his letter attached here and elsewhere on CN recently. I blacked out the name of a BAA member on the letter as I guess he would not thank me for airing it – I believe he was on a visit to Meudon at the time.

David/Dave.

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#19 Asbytec

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Posted 09 May 2013 - 04:16 PM

Norme - full us in please!

Pete


Pete, not to throw this off topic, but remember I once described the star flickering behind the rings as a flashlight in a dark, heavily wooded forest? That one. :)






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