Two points self-illuminated to astonishing intensity high in the northern sky for ~ 10-15 seconds

Weather being pleasant, I sat in my back yard to stargaze. Visibility was good, cloud cover faint. At about 9:00 PM, two points of light appeared to the NNE at about 65 degrees.
I was gazing in the general direction when they appeared, so witnessed their onset. They appeared simultaneously, then over the course of five to ten seconds, their illumination increased steadily to brighter than the forward lights of an oncoming airliner. Then, within about five more seconds, they faded back down, again steadily, back to invisible. Both lights were moving, slowly, toward the east.
I have heard this slow-flash to extraordinarily bright, brief illumination referred to as a "power up" by others who have captured similar appearances in video footage.
I remained watching for about another hour with no further activity.
My location lies directly beneath an air corridor to nearby Payne Field, in Everett, which lies about 7 miles directly to the north. There is no conceivable way the activity I witnessed could have had anything to do with local airport activity.
I am a project manager in telecommunications and information security.