Sunday Night open?


I'm wondering how it is determined in the emini S&P ( ES)......seems kinda crazy sometimes....like tonight!!
The Eur/Usd opens to some as early as 12:30 Sunday afternoon (although FX never stops trading the brokers servers do close)...any gaps in price will reflect when the index's globex opens.
I like GC on Sunday evening, ES at night rarely works for me.