The Globex session is the nearly 24-hour electronic futures market where the E-mini S&P 500 (ES) — the futures contract that tracks the same index as SPY — trades while the stock market is closed. It's where SPY's overnight price is discovered, and it builds the levels the cash session inherits at 9:30, making it essential context for the morning gap.
What happens overnight
Through the evening, the Asian session, and the European open at ~3am ET, ES trades continuously — reacting to global news, overseas markets, and economic releases. By the time the US pre-market warms up, ES has already established an overnight range, highs and lows, and often a clear directional lean. Those overnight ES levels translate directly into SPY reference points (they track the same underlying), so the futures session is literally drawing the levels you'll trade against.
Why the overnight levels matter
Overnight highs and lows, and the overnight range, act as real support/resistance in the cash session — the market remembers where it traded overnight even though the stock market was closed. A cash open that breaks the overnight high, or fails at it, is meaningful. Overnight volume matters too: a move built on thin Globex volume is less trustworthy than one on heavy participation, echoing the gap-and-go vs gap-fill logic.
The cash market opens onto a map that's already half-drawn. Globex did the overnight work; 9:30 is just when the stock traders get to see it.
Trading with it
Mark the overnight ES range — high, low, and any clear levels — and carry them into the cash session as reference points alongside the pre-market range and prior close. Whether the open respects or breaks the overnight structure is an early tell for the day's character. NoVo incorporates the overnight and pre-market structure into the live map, so the futures-session levels are already on your chart when the bell rings.