To make it look more like the sky I perceived, we first use Photoshop's Quick Mask
to create a layer mask that will essentially select the upper part of the frame
where the sky is, as shown here.

Accuracy with this step is not terribly critical. Generally anything close will do.

Briefly, to do this:

1. enter Quick Mask Mode,
2. draw a gradient from black to white using the Gradient Tool,
3. exit Quick Mask Mode and a gradient selection will automatically be created.

The same thing can be done by creating an alpha channel, drawing the gradient in
the new alpha channel, and then loading that alpha channel as the active selection.

Click 'next' to continue...