Depending on where you are during totality, it could look like the twilight that comes right after the sunset, or it might get so dark you're not able to read. But it won't be exactly like nighttime, according to Littman and Espenek. Here's what Business Insider's Dave Mosher saw on a flight through a solar eclipse in 2008:
The moon's shadow will be visible in the west, especially if you're on a hill. Littman and Espenek describe the shadow as "the granddaddy of thunderstorms but utterly calm."
About 15 minutes before the eclipse has reached totality, the environment around you will start to change. Colors will fade or take on a blue-ish hue, according to Mark Littman and Fred Espenek, authors of "Totality: The Great American Eclipses of 2017 and 2024."