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badgerchap

Transparent Sdo Venus?!

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Just watched this full transit video from SDO:

http://venustransit.gsfc.nasa.gov/data/kiosk/dataset/Venus_AIA12s_304Track/phase/track

Oddly enough, if you look carefully, you can see the surface features of the sun through Venus' disk!

Anyone know why this might be?

I have a couple of ideas, neither of which I am confident about:

1) The CCD picking up the image is retaining some energy from earlier images, causing a ghost on the CCD. My main problem with this idea is that there is a good amount of time (over a minute and a half) between images, so presumably, any ghost heat on the CCD should have dissipated? Aside from this, I have no idea whether residual heat on the CCD would cause such an image.

2) Radiation from the sun at certain wavelengths is passing through Venus? As I write this, I realise how silly it is - any form of radiation (neutrinos only really) that could pass through an entire planet, would also presumably pass straight through our CCD.

So apart from that I have no idea. I'm certain it's something fairly mundane, but interesting nonetheless!

Any thoughts?

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I noticed this too on a transit video from Nasa that I watched earlier.

I don't know the explanation, but I think it is probably more to do with light scatter than anything else. Venus is basically a rocky planet, so visible radiation won't pass through it. The contrast difference between the sun's light and venus's dark disc i think would rule out seeing any lightning activity from the dense atmosphere.

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I think what at first looks like detail from the Sun is actually just noise, I stepped through the time lapse and as Venus passes over brighter and darker patches on the Sun, the "features" seen on Venus don't really match those on the Sun.

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I think what at first looks like detail from the Sun is actually just noise, I stepped through the time lapse and as Venus passes over brighter and darker patches on the Sun, the "features" seen on Venus don't really match those on the Sun.

I dunno, I thought that you could definitely make out the sun's limb across the disk of Venus - also some of the brighter patches seemed to shine 'through'. I do agree though, probably noise and/or compression related. Nice effect though, as if Venus is like a giant Baader filter :)

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My guess would be compression. Even though the "show through" moves across the frame, I'm guessing it's a crop from a full frame rather than a view following Venus.

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Yes it does look weird, doesn't it? If you pause the movie with Venus half on the limb then it's very obvious. I suspect it's some sort of post-processing artefact. It's not simply averaging across frames, because Venus' disk looks sharp. But probably something along those lines is what's going on. They may, for instance, have an algorithm that compresses the brightness range so that it looks nice on a monitor. If that algorithm calculates stuff over the course of the whole movie but then adjusts individual frames then you may get something like what you see here.

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The presenters did explain it last night on the live NASA broadcast, but I can not remember what it was they said caused it.

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Not sure what video settings I have compared to others, but I would definitely say that that is the Sun showing through Venus.There are bright and dark spots which enter the disk of Venus, change during the migration of Venus, and then emerge in a similar pattern to the solar disk behind.

It's almost like a disk has been painted on in order to illustrate the transit, rather than an actual video, although I don't believe that to actually be the case.

In truth, I have no idea, but it looks pretty (according to the better half)!

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I found a link, it said

the effect of the sun's light shining through Venus is caused by light refraction which is apparent because we're viewing the event from so far away.

And NASA's video

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Due to refraction one can see the atmosphere of Venus when it's at the solar limb (http://physicsworld.com/cws/article/news/2012/jun/05/world-set-for-the-2012-transit-of-venus). I suspect that is what the quote is alluding to. The effect in the movie, however, is certainly a processing artefact. There, the whole planet appears to be slightly transparent and there's no way that can be real.

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