Earthshine blog

Earthshine blog

"Earthshine blog"

A blog about a system to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

Reach of halo

Post-Obs scattered-light rem.Posted by Daddy-o Jun 14, 2013 10:02AM
In considering B-V images, as here we are have to know how far the BS halo reaches onto the DS. We have looked at that before, here. We now revisit this issue. Here is a contour plot of the DS and the halo, with colours so that we can see how far the halo is likely to reach - we see it reach into the sky on the BS - how far do we think it reaches onto the DS?

Consider the yellow end of the greens, for instance - on the sky that contour lies 40-50 pixels from the BS rim - on the DS it lies adjacent to the red area which is the BS. The yellow-green contour therefore does not interfere much with most of the DS. The blue contours on the DS, howvere, are represented on the sky far away from the BS - so the blue areas on the DS may be interfered with by that part of the halo.

The above is V-band image. In B-V images we rely on much of the halo being similar in B and V and thus cancelling. The above noticeable gradient in DS brightness is absent in the B-V image.

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Posted by Chris Flynn Jun 18, 2013 03:02AM

One definite issue here is that the V and B band PSFs differ significantly on short scales -- and I haven't looked at the powerlaw falloff in the B band yet in enough detail to be sure that the halos come close to canceling out in the B-V images! I will look at this asap! - Chrsi