Picture this: The day starts off bright and sunny. Then, a bit later, you begin to notice that, although it is still sunny, the day doesn't seem quite so bright. And still a little while later, it almost seems like some big storm is brewing. Then, suddenly, and without any warning, the midsummer day turns strangely dark.
A few stars come out. Birds and animals become confused and quickly head home to sleep. Night insects begin to chirp. All around the horizon, there is a strange yellow-orange glow resembling a weird sunset. And meanwhile, up in the sky where the sun should be, there appears instead a jet-black disk surrounded by a softly glowing halo.
Then, just as suddenly, the sky brightens up. The stars disappear, birds and animals awaken, and the sun returns.
What you have just witnessed is a total eclipse of the sun.
This total solar eclipse of 2017 will be the first time in nearly four decades that such an event will be visible so close to home. "Close," of course, is a relative term. But for most Americans, this spectacular phenomenon will occur literally in their own backyards.
Contrary to popular belief, total solar eclipses are not particularly rare. Astronomers predict 68 to take place during the present century — one about every 17.6 months. On such occasions, the moon casts its dark, slender cone of shadow (called the umbra) upon the Earth's surface.