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Light doesn't escape a black hole because it's too slow, or because something is holding it back. It travels at its usual speed - but beyond the event horizon, every path leads not outward but inward. The direction "away" simply doesn't exist there.
Read the articleThe event horizon is neither a wall nor a surface. It is the line beyond which every path, including light paths, leads only inward. You can cross it without noticing, but seeing this from the outside is almost impossible.
Read the articleOrdinary ones form in a way we understand: a massive star runs out of fuel, and its core collapses. But the origin of the giants at the centers of galaxies is still an open question - they are too massive and appeared too early.
Read the articleThe honest answer: we don't know. The equations work up to a certain point, then stop producing a meaningful result. What we do know is what happens on the way in, and it is described in considerable detail.
Read the articleOne telescope wouldn't have been enough: we needed an antenna the size of a planet. It was assembled from observatories on different continents, all observing the same point at the same time.
Read the articleIt is the prediction that black holes are not completely black: they glow very faintly and slowly lose mass as a result. It has not yet been verified because the radiation is so weak that it cannot be distinguished from the background.
Read the articleThe calcium in your bones and the iron in your blood were not created with the Universe. They were forged inside stars - and only then were you made from this material.
Read the articleThere are huge numbers of stars, a huge amount of time has passed, and by rough estimates, signs of alien life should have turned up. They haven't. Many explanations have been proposed, and for now, all remain equally plausible: we have no basis for choosing between them.
Read the articleWater matters not on its own, but as a medium where molecules meet and react. In theory, another liquid solvent could replace it - liquid methane or ammonia are the options scientists discuss - but each is worse in important ways.
Read the articleThere's a formula that multiplies several factors: how many stars are born, how many have planets, and so on. It doesn't give us an answer, but it shows exactly what we don't know.
Read the articleNo one searches for organisms directly. They look for places where water can stay liquid, there is an energy source, and there is carbon. Four such places come up most often - and on 3 of them, the ocean is hidden beneath ice.
Read the articleThe question sounds simple: there are unimaginably many stars, there has been enough time, and someone should have shown up by now. There is no answer, but there are several explanations - and each is disturbing in its own way.
Read the articleWith their eyes closed in the dark, crew members see brief flashes and streaks. It's not fatigue: charged particles from cosmic radiation pass through the eye and brain.
Read the articleIn orbit, your body stretches out within a few days - gaining up to about 3% of your height: for someone 175 cm tall, that's about five centimeters. Your bones don't lengthen - your spine straightens, and the intervertebral discs absorb water that your body weight squeezes out of them on Earth. Back home, everything returns to normal within a few days.
Read the articleIt's not just weak muscles. Over months in weightlessness, the vestibular system adapts, fluids redistribute, and bones weaken - and on Earth, you have to relearn how to cope with all these changes.
Read the articleIn weightlessness, your body doesn't break - it quickly adapts to a world with no "down." Fluid shifts to your head, bones and muscles lose their load, and your inner ear loses its point of reference. The hardest part comes when gravity returns.
Read the articleA sleeping bag is fastened to the wall, and you can sleep upright, lying down, or upside down all at once - it makes no difference. The harder part is this: the station has sixteen sunrises in 24 hours, so you have to keep your body clock on schedule with routines and light.
Read the articleIt's motion sickness in reverse. In weightlessness, the vestibular system stops telling you which way is down, while your eyes keep showing you the floor and ceiling, and your brain responds to the contradiction with nausea.
Read the articleThe Moon does rotate on its axis - it just takes exactly as long as it does to orbit Earth. Earth's tides slowed it down this way. And because it wobbles slightly, we get to see not exactly half its surface, but about 59 percent.
Read the articleThe Moon pulls more strongly on the side of Earth facing it than on the far side. Because of this difference, the water stretches into two bulges, one on each side of the planet. Earth rotates beneath them, so high tide comes twice a day.
Read the articleThe Moon is too large to be a rock captured by chance. The best explanation: about 4.5 billion years ago, a body roughly the size of Mars struck the young Earth, and the Moon formed from the debris thrown out.
Read the articleMore than a hundred tons of human-made items lie on the Moon: ascent stages, instruments, tools, flags, bags of trash, and even a memorial plaque bearing the names of those who died. Some of it still works.
Read the articleNear the horizon, the Moon looks huge, while overhead it looks ordinary, even though its size in a photo is the same. This perceptual illusion has been known for thousands of years, and there is still no single explanation for it.
Read the articleMars is red not because of heat, but because of rust: iron in its rocks combined with oxygen to form oxides - the same compounds that give a rusty nail its color. This rusty layer is thin, and beneath it the planet is dark gray.
Read the articleAn Italian astronomer described fine lines on Mars and called them by a word meaning waterways or channels. In English, the translation became a word implying human-made structures - and for half a century, Mars became a planet with engineers.
Read the articleA Martian day is about forty minutes longer than an Earth day. A small difference - until you have to live by it: rover teams switched to local time and, within a couple of weeks, ended up completely out of sync with Earth.
Read the articleThe main challenge isn't the engines. We know how to get there: spacecraft land there regularly. The problem is that people would have to spend months in transit, endure radiation, survive the landing and then return, without enough fuel on board for the trip back.
Read the articleYes, there was - not just puddles, but rivers and lakes. That was about 3-4 billion years ago. Today, liquid water cannot remain on the surface, but not all of it is gone: some froze, some is bound in rocks, and some escaped into space.
Read the articleFrom the mid-17th century, sunspots almost completely disappeared for nearly 70 years. Observers kept records, counting only single digits where there were usually thousands. This coincided with the coldest stretch of the Little Ice Age.
Read the articleA flare is not a fuel explosion. The Sun rotates at different speeds, gradually twisting its magnetic field into tight loops. When the tension becomes too great, field lines break and reconnect into a simpler shape, and energy built up over weeks escapes in minutes as light, X-rays, and accelerated particles.
Read the articleThe Sun doesn't burn - there is nothing there to burn, and no oxygen. In its core, hydrogen fuses into helium, and part of its mass becomes energy. The surprising part: per cubic meter, the core gives off less heat than your body. The Sun shines because it has an incredible number of those cubic meters.
Read the articleThe Sun constantly blows a stream of charged particles into space. Earth's magnetic field deflects it, and usually the story ends with auroras - but powerful eruptions can affect satellites, communications and power grids.
Read the articleIn a few billion years, the Sun will use up the hydrogen in its core, swell into a red giant, and engulf the nearest planets. But life on Earth will become impossible much sooner: the Sun's luminosity is already gradually increasing.
Read the articleLight travels fast, but not instantly. While it reaches your eye, time passes - and you see not what exists now, but what was. For the Moon, it's fractions of a second; for Andromeda, 2.5 million years.
Read the articleTwinkling is caused by the air, not the star: layers at different temperatures refract light differently. A star is a point, so its entire beam is shifted at once; a planet is a tiny disk, so fluctuations in different parts cancel each other out.
Read the articleA star's color is its surface temperature. A red one glows at about 3,000 degrees, a blue one at tens of thousands. The yellow Sun sits closer to the cool end of the scale than you might think.
Read the articleA star begins as a cold cloud of gas and dust that collapses under its own weight. As it contracts, it heats up, and when the center becomes hot enough, reactions begin, turning the cloud into a star.
Read the articleTwo things remain: a dense remnant at the center and a cloud of matter flying outward. What ends up at the center - a ball of neutrons or a black hole - depends on the star's mass, while the cloud becomes material for future stars and planets.
Read the articleMercury rotates slowly on its axis but races around the Sun. As a result, about 176 Earth days pass from sunrise to sunrise there, exactly two local years.
Read the articlePluto didn't change or disappear. The definition of a planet changed because similar bodies were found beyond Neptune's orbit, and one of them turned out to be at least as large as Pluto. The choice was between a new rule and a growing list of planets.
Read the articleVenus's surface is about +460 °C - hotter than Mercury, even though Mercury is nearly twice as close to the Sun. The reason isn't distance but air: it exerts more than 90 times Earth's pressure and is almost entirely carbon dioxide. It lets light through but barely lets heat escape.
Read the articleThe rings are chunks of ice that cannot come together to form a moon. So close to the planet, its gravity pulls any cluster apart more strongly than the cluster can hold itself together. Instead of a moon, you get a rotating disk of debris.
Read the articleUranus's axis is tilted almost at a right angle, so the planet rolls along its orbit like a wheel rather than spinning like a top. Most likely, it was caused by an early impact: something large struck the young planet and knocked it over.
Read the articleThe Red Spot is a storm that has been spinning longer than photographs have existed. Earth would fit inside it, its edge winds are stronger than those of any hurricane, and the biggest mystery isn't where it came from, but why it still hasn't ended.
Read the articleThere is no boundary you could land on. The gas becomes denser as you go down, without any sudden change, gradually turning into a liquid, and deeper still into matter that behaves like a metal. A probe would stop existing long before it encountered anything resembling a surface.
Read the articleIf the universe were infinite, eternal, and unchanging, every line of sight would eventually end at a star, and the entire sky would glow like the surface of the Sun. It is dark because the universe is not infinitely old, and light from the most distant stars simply has not had time to reach us.
Read the articleIt isn't matter flying away from some point. It's space itself expanding between galaxies. That's why expansion has no center: from any galaxy, the view looks the same, as if all the others are moving away.
Read the articleAccording to the equations, matter and antimatter should have been created in equal amounts, and when they meet, they annihilate each other. In that case, nothing would be left in the universe except radiation. We exist, so there must have been an imbalance somewhere. No one knows where it came from.
Read the articleThe age is estimated in three independent ways: from ancient radiation left over from the early Universe, from the expansion rate, and from the ages of the oldest stars. All three give about 14 billion years, and that agreement is the strongest evidence.
Read the articleThe honest answer is that nobody knows, and the question itself may be flawed. If time began with expansion, there is simply nothing for the word "before" to refer to. There are hypotheses, but we have no way to test them yet.
Read the articleThere was no explosion in the usual sense. There was no point in empty space that burst, with fragments flying outward. There was a very hot, dense phase - everywhere at once - after which distances between everything began to grow. An explosion spreads out through space. Here, space itself is growing.
Read the articleAstronaut selection works like a funnel: most stages look not for strengths, but for reasons to reject you. On paper, they check your degree, experience, and body. More often, what decides it is whether you can work side by side for six months with people you can't get away from.
Read the articleThe body is restored through a program that takes weeks. The harder part turns out to be returning to a life where you make your own decisions, crowds surround you, and the work you devoted years to is already over.
Read the articleThe main enemy on a space station is a crumb. In weightlessness, it does not fall, but floats into equipment and lungs. That is why the menu is built around food that does not crumble, and ordinary bread is not taken to the station.
Read the articleThe most common activity is looking out the window. Almost every crew mentions it, and the station has a separate module with large windows for this. The rest is much like leisure on Earth, just in zero gravity.
Read the articleThis is what people call a shift in perception described by those who return from orbit: the whole planet in a single view, a thin strip of atmosphere, and none of the borders that once seemed so important.
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1500 articles across 28 topics. A quiz after each one, and every read grows your streak and level.