Before & After:
For starts, let’s use this image: 1858344 © riekephoto 123RF.com. Re-name it as “landscape”.
Preparing the night sky.
We are going to mask the sky as we will be creating our own sky. You may use the Magic Wand Tool. Otherwise, apply the Pen Tool and create vector paths along the landscape. Once complete, click on the Create Mask icon.
Create a new layer. Using the Gradient Tool, drag and create a gradient with these two colors - #003445, #000b2e. To set the colors, look for the color palettes at the Tools bar or the Color box. Click on the first palette (Foreground) and the Color Picker settings will appear and key in the first color code. Then do the same with the second palette (Background) for the second color.
Create another layer and fill it with black. Then, go to Filter > Render > Noise (Amount: 5%; Gaussian; Monochromatic). Go to Image > Adjustments > Levels to adjust the levels of this layer. Adjust to Input Levels: 0, 0.65, 255 - to reduce the amount of white dots. Set the Blend mode as “Screen”. This acts as stars in the sky.
We can also add in different star sizes simply by duplicating this layer, and then scaling it bigger. Further adjust the levels to reduce the amount of bigger stars.
Changing the landscape's color and brightness.
Having prepped the sky, the mountain landscape now looks a bit too bright for night. So, we are going to reduce brightness by adjusting the curves (Go to Image > Adjustments > Curves). Do this whilst the “landscape” layer is selected.
Notice that there are still some sunset hues on the mountain? Select those areas, and then feather the selections at Select > Feather. Proceed to change the Hue/Saturation (Go to Image > Adjustments > Hue/Saturation). Here’s my choice of settings.
The color of the lake doesn't really reflect the color of the sky. So I created a new layer, and then from the base of the layer, click and drag a soft gradient using the same colors of the sky. Change the Blend mode to “Color” and set layer opacity to 50%.
Planning the aurora's pattern and perspective.
Draw guidelines on how you want to pan out the aurora effect. I'm going to create separate layers for each of the lines - naming it “left”, “middle” and “right”.
We shall start with “right” first. Hide the other 2 lines. Go to Filter > Blur > Motion Blur. Settings may defer slightly but here’s mine - Angle: 80°; Distance: 50 pixels.
Create duplicate copies of “right” (about two or three layers) and merge them together. This will increase its opacity after being blurred.
Click on the masking icon, and mask the top off using a soft black Brush.
Reset the color palette (D), and create a new layer as “right-rays”.
Fill in White, and then go to Filter > Render > Fibers. Apply these settings - Variance: 15; Strength: 4.
Next, go to Filter > Blur > Gaussian Blur. Set Radius at 5 pixels.
Then, go to Filter > Blur > Motion Blur. Set Distance at 235 pixels.
Change Blend mode to “Screen”.
Transform this layer so effect fits the image’s perspective.
Adjust the levels.
Merge “right” and “right-rays” together. When merged, the Blend mode of the new layer will return to “Normal” resulting in the reappearance of the dark, black areas. Just set the Blend mode back to “Screen”.
Draw a rough selection on how you envisioned the aurora's shape, feather it…
… and mask it away.
Moving on to “middle”.
Apply Filter > Blur > Motion Blur. Here are my Motion Blur settings...
When complete, duplicate the layer a few times and merge them together for increased opacity.
Mask off the excessive areas. Try to mold it into similar shape, as below:
For “left”, I applied the methods similar to “right, but created larger gaps on my Filter layer (see below steps 3 to 5). Once I’ve merged my “left” and “left-rays” layers, I further tweaked my settings at “Levels” for a softer look (see step 6).
Once done, we can merge all 3 layers “left”, “middle”, and “right” together. Rename it as “aurora”. Again, set the Blend mode back to “Screen”.
Next up, applying colors to the aurora.
Create a new layer as “color”. Using a soft Brush, draw streams of lines like this:
Next, apply Filter > Blur > Gaussian Blur.
Then, change its Blend mode to “Overlay”, and set opacity to 80%.
Create reflections on the lake.
Duplicate “aurora”, flip it, and give it a little perspective. Set opacity to 40%.
Duplicate “color”, flip it. Erase those areas that touched the mountains. Set opacity to 65%.
We can further reduce the brightness and introduce some more blue to the image:
In my final image, I've altered the contrasts and hues of the image, and strengthened the shine of the stars. For an extra touch, I’ve added some clouds at the center to enhance the overall look and feel of the image.