photoshop sky swap

this week's photoshop assignment was to swap out the sky in an image with a night sky. here's the before shot, a photograph of the statue of Peter Pan in London, taken from Google:



and here's the after shot, sky switched with a tweaked photograph of the Aurora Borealis, also from Google:



i totally underestimated the difficulty of the assignment; instead of taking me an hour or two, this took about 4-5 hours to get done O_o but selections and masks are now officially the most helpful tools i've encountered in photoshop :D thanks in advance for looking!