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Of course, estimating one’s relative lifetime exposure to daylight versus artificial light is tricky at best, so we have to make do with a proxy: Everything else being equal, “night owls” could be expected to be exposed to more artificial light than those who rise at the crack of dawn and go to bed early.

Some are empty, set up at the crack of dawn and then abandoned for hours on end, until the owners actually want to use them.

Hundreds of customers camped outside a department store at the crack of dawn.

That means long, circuitous routes that require students to be outside at the crack of dawn for an hourlong ride that could be done in 15 minutes in a parent’s air-conditioned car.

At the crack of dawn, I’m picked up at my hotel by Maximiliano Valdivieso, a guide who will take me to Mylodon cave located outside the city.