What the Helen of Troy is This

What the Helen of Troy is This?

“Dear PoPville,

but every night between 9:30-10pm for the past couple of weeks, there is a bright white light in the sky over upper NW DC (likely near / above the National Cathedral). But it’s high up!!! So I’m not sure if it’s a helicopter… and then after a while, it’s gone! It’s definitely bigger and brighter than a star. What is it?!? Who’s watching us?!? PS: It stays stationary in the exact same spot for at least half hour… and then it quickly disappears!!!”

Ed. Note: I thought it might be the oft reported imaging balloon but we’ve never had a night reporting before. Any ideas?