Rain on the sun?
Rain on the sun? 
Sometimes the most familiar things can be the most surprising. So how about this? Our Sun (that big ball of nuclear fire in the sky) has long-lost siblings – and it rains on the Sun.

Right now, our Sun is pretty lonely – over four light years from its nearest neighbour, Alpha Centauri. But its birth wasn't solitary. Like most stars, our Sun condensed from a vast molecular cloud of dust and gas (mostly hydrogen and helium, but with other trace elements). Around 4.6 billion years ago, the Sun was most probably born in a cluster of perhaps 1000 other stars – all from the same cloud.

The astronomers went looking, and found some stars with the same trace elements, and in the same ratios, as our Sun. They also did a kind of "galactic archaeology", using complex mathematics to "rewind" the motions of the stars over the last 4.6 billion years – back to that primeval cloud.

Against all odds, the astronomers have found what is almost certainly one of our Sun's siblings. It's about 110 light years away in the constellation Hercules, and has the rather unromantic name of HD 162826. It's a little bigger than our Sun, and a little hotter – but it's the same age, because it was born at the same time. (We don't know if, like our Sun, it has planets.)

So the Sun has at least one sibling that we know of, but how can it possibly have "rain"? After all, down in the Sun's core where hydrogen is turned into helium, the temperature is around 15,000,000 degrees. Even on the surface, it's about 5500 degrees.

OK, the Sun's "rain" is not made from water, but it does fall down just like rain does, here on Earth.
On Earth, there is the so-called water cycle. Water vapour forms (say, over the oceans), and it rises upwards to make clouds. As these clouds rise further to a few kilometres of altitude, they cool – and they can condense into little water droplets, which then fall down as rain.

These droplets are a few millimetres across. (Note that in this cycle, water undergoes changes of state, with liquid first turning into gas, then turning back into a liquid.)
On the Sun something similar happens – but it's with plasma, and the scale is so much bigger. The Sun doesn't really have a hard surface, but there is a boundary between its main body and its atmosphere (which is called the "corona"). This coronal rain was predicted some four decades ago, but only recently have our more advanced telescopes seen it.

Via various processes, the super-hot plasma from under the Sun's surface gets squirted to a height of about 60,000 kilometres, cools to about 60,000 degrees, and then falls down again.
One difference from Earth's rain is that there is no change of state – the plasma remains as plasma. The other big difference is the size of the droplets – they're about 100,000 square kilometres, or roughly the size of Tasmania.

And when they fall, they plummet down to the Sun's surface at up to 50 kilometres per second. This is slow – it "should" be a lot faster, thanks to the Sun's enormous gravity. But it appears that the falling "raindrops" are cushioned by a huge layer of hot gas – which slows them down.