Why would DOW/S&P futures moving now (Sunday night) when the U.S. market is closed tomorrow for President day?

I'm having a bit of trouble understanding the DOW and S&P futures. I've read the few articles on investopedia, which stated that the futures are based on contracts traded on CBOE at 820EST, 1 hr prior to market open. If that's the case, why am I seeing movement in the futures indexes on Sunday night when the market is closed on Monday.

Thanks!

Submitted February 18, 2018 at 08:01PM by Cosmos1980 http://ift.tt/2FdZs3J