Create a new layer, about the background's one and select the Pen Tool to represent the mountains' silhouette.



The layer's Opacity should be on 20%.



Select the Ellipse Tool on a new layer and press the shift button to represent the sun's silhouette.



Then we have to represent the luminescence around the sun, that is why we need to copy the sun's layer and blur the copy out, applying the next option: Filter ? Blur ? Gaussian Blur.



To make the luminescence more intensive, we'll copy several times the layer in case: Layer ? Duplicate Layer (ctrl+j).