The Moon is a mystery. Everyone on Earth can see it, but we only ever see one side of it. It affects the tides of the ocean, when animals have sex and apparently even how people sleep. Yet until 1969, no one had ever been to the Moon. Even in 2015, almost a half-century later, only a measly 12 people have been there.
Don't panic, but our planet is doomed. It's just going to take a while. Roughly 6 billion years from now, the Earth will probably be vaporized when the dying Sun expands into a red giant and engulfs our planet. But the Earth is just one planet in the solar system, the Sun is just one of hundreds of billions of stars in the galaxy, and there are hundreds of billions of galaxies in the observable universe. What's in store for all of that? How does the universe end?
This was the most-read story on BBC Earth in 2015. Here is another chance to read it. It could happen to anyone. Maybe you're out trying to find a new habitable planet for the human race, or maybe you're just on a long walk and you slip. Whatever the circumstances, at some point we all find ourselves confronted with the age-old question: what happens when you fall into a black hole?
James Joyce described it as snot-green. Lord Byron went for plain old dark blue. Homer's was frequently "wine dark". These literary greats were describing the colour of the sea, and the variation in their prose wasn't just poetic licence.
The recent film The Theory of Everything tells the story of Stephen Hawking, who managed to become a world-famous physicist despite being confined to a wheelchair by a degenerative disease. It's mostly about his relationship with his ex-wife Jane, but it does find a bit of time to explain what Hawking has spent his career doing.
Chris McKay's quest for extraterrestrial life started in 1976, when Viking 1 and 2 landed on Mars. Touching down on Mars for the first time was a big deal, sure, but the then-first-year graduate student was especially excited because the landers found what appeared to be signs of Martian life.
All things must pass. That includes life on Earth, which will surely be wiped out eventually. But how long does it have? The fossil record tells us that life on Earth has lasted at least 3.5 billion years. In that time it has survived being frozen, clobbered by rocks from space, mass poisoning, and even lethal radiation. Clearly, it's hard to completely sterilise the planet. But there's no shortage of potential apocalypses. Which of them will finally render the Earth barren?
There's egg on your face, literally. You tried to juggle some eggs, it all went wrong, and now you've got to shower and change your clothes. Wouldn't it be faster to just un-break the egg? Breaking it only took a few seconds, so why not do that again, but in reverse? Just reassemble the shell and throw the yolk and the white back inside. You'd have a clean face, clean clothes, and no yolk in your hair, like nothing ever happened.
People have wrestled with the mystery of why the universe exists for thousands of years. Pretty much every ancient culture came up with its own creation story - most of them leaving the matter in the hands of the gods - and philosophers have written reams on the subject. But science has had little to say about this ultimate question. However, in recent years a few physicists and cosmologists have started to tackle it.