Open Photoshop and then open all the photo segments (so all the photo segments are open at the same time).
Go under Photoshop's File menu, under Automate, and choose Photomerge.
In the resulting dialog, from the Use pop-up menu, choose Open Files. Make sure the Attempt to Automatically Arrange Source Images checkbox is turned on, and then click OK.
When the main Photomerge dialog appears, it will stitch the photos together into one seamless panorama (well, as long as you followed the rules laid out earlier). If you see a small seam at the top, between two segments, go ahead and click OK anywaychances are it will be gone when the final image is created. If for some reason it's not, use the Clone Stamp tool (S) to cover it by pressing-and-holding the Option key (PC: Alt key) and clicking nearby in an area of sky that looks similar to sample that area. Then, choose a soft-edged brush from the Brush Picker and clone (paint) over the little seam to hide it.