What would happen to the world if the sun went out?

By the middle of the 21st century, humanity has managed to overcome a series of catastrophic events and maintain some sense of stability. Space exploration has begun again. Science has led the way.

But then one day, the sun goes out. Solar panels are useless, and the world begins to freeze.

Earth begins to fall out of its orbit.

The end is nigh.

Someone has sent us a sign.