Space
20 explanations and counting.
What is an asteroid?
Asteroids are lumps of rock and metal left over from the birth of the Solar System. Most orbit quietly between Mars and Jupiter — but some cross Earth's path, and we're now learning how to deal with them.
What is a space station?
A space station is a home in orbit — a place where astronauts live and work hundreds of kilometres above Earth, moving so fast they see 16 sunrises every single day.
How does the James Webb Space Telescope work?
Webb can see galaxies that formed just a few hundred million years after the Big Bang. It does this by catching light that has been travelling for nearly 14 billion years — here's how.
What is the cosmic web?
Zoom out far enough from Earth and the universe stops looking like empty space — it looks like a giant spiderweb made of galaxies. Here's what that actually is.
Why are astronauts weightless in space?
Astronauts float around the space station — but Earth's gravity is nearly as strong up there as on the ground. So what's actually happening?
What is a neutron star?
When a star dies in a supernova explosion, sometimes what's left is an object the size of a city but more massive than the Sun — where a teaspoon of material would weigh a billion tonnes.
What is the International Space Station?
A football-pitch-sized laboratory has been continuously inhabited in orbit since 2000. Here's what happens up there — and how it stays in the sky.
What is a solar eclipse?
The Moon is 400 times smaller than the Sun but also 400 times closer. This coincidence produces one of the most spectacular events visible from Earth.
What are galaxies?
Our Sun is just one of 100–400 billion stars in the Milky Way. And the Milky Way is just one of roughly 2 trillion galaxies. Here's what they are and how they form.
What would happen if the Sun disappeared?
The Sun is 149 million km away. It drives our weather, feeds all life, and holds the Solar System together. What would happen without it?
Could humans live on Mars?
Mars is the most Earth-like planet in the Solar System. But "most Earth-like" still means freezing, airless, and bombarded with radiation. Could we live there anyway?
What is a comet?
Comets are ancient, dirty snowballs left over from the formation of the Solar System — and when they get close to the Sun, they put on one of nature's finest shows.
How is a star born?
Stars don't just appear. They form over millions of years in vast clouds of gas and dust — and the process is one of the most dramatic in the universe.
What are exoplanets?
Until 1992, we only knew of planets in our own Solar System. Since then, we've found thousands of worlds orbiting other stars — and some look very familiar.
What is dark matter?
About 27% of the universe is made of something that doesn't emit light, doesn't absorb light, and can't be directly detected. We know it's there — but not what it is.
How do rockets work?
Getting to space requires escaping Earth's gravity with nothing but controlled explosions. Here's the physics of how rockets actually work.
How big is the universe?
The universe is so big that the numbers stop making any kind of intuitive sense very quickly. Let's try anyway.
Why does the Moon affect the tides?
Twice a day, the ocean rises and falls by several metres — and it's all because of a rock 384,000 km away. Here's the physics.
What is the Big Bang?
The entire universe — every star, planet, galaxy, and atom in existence — began about 13.8 billion years ago in a single, almost incomprehensible moment.
What is a black hole?
A place in space where gravity is so strong that not even light can escape. Yes, really.