Solar batteries let you store excess solar energy to use later. Here’s what they cost, how they work and when they’re worth ...

Our Sun’s outer atmosphere, the corona, is millions of degrees hotter than it should be, and no one knows why.

The workings of our solar system are roughly the same now as they have been for millions of years. Moons circle their planets, the planets circle the sun, the sun’s magnetic fields and sunspots wax ...