Sunset

Chris: Yesterday when the sun was setting I saw a castle out that way.
Alex: You should tell Erin. She'd like that.
Chris: Well it wasn't really a castle. It was a big building. But you can only see it when the sun is behind us. Then it reflects off the top.

At sunset Chris found Erin and brought her to the window. It was a clear day, and the flatness of the desert made it feel like you could see forever. When the sun had almost gone below the horizon the building appeared as a shiny specter. Only the top was lit, which made it appear to float in the air.
Erin: Wow... that is pretty.
Chris: I'm surprised it's there at all. And that we haven't seen it before. Maybe you can only see it on a totally clear day.
Erin: That must be illegal, how few lights they're using. It doesn't look illuminated at all. Except for the sun.
Chris: How long does an alien occupation usually last?
Erin: Haha, there isn't any usual outside of science fiction. Why are you thinking about it?
Chris: I just want to be able to talk to people without it having to go through an automatic translator.
Erin: You wouldn't be able to talk to me without it.
It was true; Erin wasn't from Earth.
Chris took his frustration out on the translation algorithm by calling Erin a made-up word. She must have heard something else because she answered "I can't".

Next day Chris had disappeared. Erin waited for sunset to watch the castle and imagine Chris had gone there.
Alex found her standing by the window.
Alex: Wow, there really is a castle.
Erin: That can't be legal, can it? Using no lights like that?
Alex: I have trouble believing it's even real.
Erin: Let's measure it, though.

They got a spectrometer and found that the total power emitted was many times below the legal minimum.
Alex: Unless there's something way down in radio waves, or way up in gamma rays.
Erin: That would be scary.
Alex: It would be fitting.