[ATMoB-discuss] Mercury Transit results - diffraction?

[John Boudreau]

----- Original Message ----- 
From: "Gary Jacobson" <gdjacobson at verizon.net>
To: <atmob-discuss at atmob.org>
Sent: Friday, November 10, 2006 8:33 PM
Subject: [ATMoB-discuss] Mercury Transit results - diffraction?


> On the APOD image that Dan provided the link for, there is a circular feature
> around Mercury.
> Is that likely to be a chance alignment of granulation on the solar surface, or
> a diffraction affect?
> 
> Gary Jacobson

Hi Gary,

It's either a chance alignment of a bright granulation feature and/or an artifact from the wavelet sharpening processing used by the photographer. I really tend to think it's the latter. He's mentioned on the RegiStax Yahoo Group that he used the new RegiStax v4 to process the image, and that has a wavelet sharpening routine with up to 6 layers available. I've seen another transit image he took that doesn't show the effect as strongly, but it's certainly not processed as aggressively as his APOD image. The immediate area of transition from solar disc features to the sharp edged, stark black silhouette of Mercury would make it particularly difficult to avoid a bright artifact at the planet's limb during sharpening. 

Overall, I think he's done a pretty nice processing job on the image. In a case like this even if there was no processing-induced halo artifact surrounding Mercury, we may see a faint one anyway. Our brains interpret our vision with a sharpening routine that produces some of the same artifacts that can occur in digital image processing.

---John


> 
> 
> -----Original Message-----
> From: atmob-discuss-bounces at atmob.org [mailto:atmob-discuss-bounces at atmob.org]
> On Behalf Of Dan Winchell
> Sent: Friday, November 10, 2006 10:54 AM
> To: David Aucoin; atmob-discuss at atmob.org
> Subject: Re: [ATMoB-discuss] Mercury Transit results
> 
> 
> Take a look at the "Astronomy Picture of the Day" for today.
> 
> http://antwrp.gsfc.nasa.gov/apod/astropix.html
> 
> I think that is the best shot I have seen of the event.
> 
> -  Dan Winchell
> 
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