[Gimp-user] Any way to set a layer to be semi transparent?

[Seldom <forums gimpusers com>]

I'm an ex Photoshop user who does astrophotography (AP).  In AP we frequently
shoot a number of photos that we then stack in layers to reduce noise or create
color channels.  One problem with stacking is that the sky may move between
photos. (It's called field rotation.)  This can be corrected if the stack is
aligned properly.  While Photoshop has a number of automated stitching
techniques available, I can't find any of these in GIMP.

I could manually align layers in stacks if I could reduce the transparency of
one layer relative to the layer below it.  Is this possible?

-- 
Seldom (via www.gimpusers.com/forums)