Photoshop CS4 Assistance

[M Freedman]

In Photoshop CS4 I am trying to take the attached image and adjust the dark area at the lower right of the image to match the background sky value the rest of the image contains, for the sky background.  I have forgotten how to do this - can someone help?  I have already applied Astronomy Tools v1.6 on the image.

Thanks very much.

Edited February 8 by Cornelius Varley
background colour to text removed

[ollypenrice]

Probably impossible. There seems to be little or no signal in the dark band to stretch.

However, what I would normally do is:

Copy layer, top layer invisible, bottom layer active.

Curves. Put a fixing point at the level of the brightest background sky and several fixing points above that. 

Lift the bottom part of the curve below all the fixing points.

Top layer visible and active. Erase the dark sections with a feathered eraser.

I think that, at some point in your processing, the black point has been clipped in that lower edge. If it has, you need to start again from the linear and avoid clipping.

Olly