Space & Astronomy

Gravity works because every object with mass attracts every other object. Einstein's deeper explanation: mass curves the fabric of spacetime, and other objects follow that curve — which we feel as the pull of gravity.

The Sun produces energy through nuclear fusion in its core. Under crushing pressure and heat, hydrogen atoms fuse into helium, releasing enormous amounts of light and heat. That energy travels out and reaches Earth as sunlight.

A star forms when a giant cloud of gas and dust collapses under its own gravity. As it shrinks, the center grows incredibly hot and dense until nuclear fusion ignites — and the star begins to shine.

Moon phases happen because we see different amounts of the Moon's sunlit half as it orbits Earth. The Moon doesn't make its own light — it reflects the Sun's — so as its position changes, the lit portion we see grows and shrinks over about a month.

A solar eclipse happens when the Moon passes directly between the Sun and Earth, casting its shadow on us. For a few minutes, the Moon blocks the Sun's light, turning day briefly to twilight along a narrow path.

An orbit is the result of an object constantly falling toward another due to gravity, while moving sideways fast enough that it keeps missing. The Moon, satellites, and planets are all 'falling' around a bigger body — endlessly curving instead of crashing.

The seasons happen because Earth is tilted on its axis as it orbits the Sun. The tilt means each hemisphere leans toward the Sun for part of the year — getting more direct light and longer days (summer) — and away for the rest (winter).

The northern lights (the aurora) happen when charged particles from the Sun crash into gases high in Earth's atmosphere, making them glow. Earth's magnetic field funnels these particles toward the poles, which is why the lights appear there.

A black hole forms when a massive star runs out of fuel and collapses under its own gravity. The matter is crushed into an incredibly dense point, creating gravity so strong that not even light can escape past its boundary, the event horizon.

A supernova is the explosive death of a star. When a massive star runs out of fuel, its core collapses and rebounds in a colossal explosion — briefly outshining a whole galaxy and scattering elements that form new stars, planets, and even us.

A comet is a chunk of ice, dust, and rock that orbits the Sun. As it nears the Sun, its ice heats and turns to gas, releasing dust that forms a glowing head and a long tail that always points away from the Sun.

Earth's magnetic field is generated deep inside the planet, where the swirling molten iron of the outer core acts like a giant dynamo. This churning, electrically conductive metal creates electric currents that produce a magnetic field stretching far into space.

A telescope works by gathering far more light than your eye can and focusing it to form a magnified image. A large lens or mirror collects light from distant objects, making faint, far-away things like galaxies bright enough to see.

Rockets work by Newton's third law: they burn fuel to shoot hot gas out the back at high speed, and the equal and opposite reaction pushes the rocket forward. Unlike a jet, a rocket carries its own oxygen, so it can work even in the vacuum of space.

A rocket engine works by burning propellant to produce a huge volume of fast-moving exhaust gas and throwing it backward out of a nozzle. By Newton's third law, pushing that mass backward thrusts the rocket forward — and because it carries its own oxidizer, it works even in the vacuum of space.

A lunar eclipse happens when Earth passes directly between the Sun and the Moon, so Earth's shadow falls on the Moon. This alignment occurs only at full moon, when the Sun, Earth and Moon line up in space.

A supermoon happens when a full moon coincides with the moon's closest approach to Earth in its elliptical orbit, making it appear slightly larger and brighter. Because the moon's distance varies by up to about 50,000 km, a full moon near perigee can look up to 14% wider and 30% brighter than one at its farthest point.

Meteor showers happen when Earth passes through a stream of dust and grit left behind by a comet, and those particles burn up in the atmosphere. Each particle hits the air at tens of kilometres per second, heating it white-hot in a streak we call a meteor.

Planets form from a disk of gas and dust around a young star, where tiny grains stick together into larger bodies. These bodies grow into planetesimals and then planets, with rocky planets near the star and gas giants farther out.

The Moon formed when a Mars-sized body struck the young Earth, blasting debris into orbit that gathered into the Moon. This giant-impact idea explains the Moon's lack of a large iron core and its similar oxygen chemistry to Earth.

Solar flares happen when twisted magnetic fields in the Sun's atmosphere suddenly snap and reconnect, releasing stored energy. This energy accelerates charged particles and heats plasma, producing a burst of radiation across the electromagnetic spectrum.

Sunspots form where intense bundles of magnetic field poke through the Sun's visible surface, cooling those patches by blocking the flow of hot plasma from below. Because they are cooler than their surroundings, they look dark against the brighter photosphere.

Saturn's rings likely formed when a small moon or comet drifted too close and was torn apart by Saturn's gravity, or when leftover icy debris from the planet's formation never coalesced into a moon. The fragments settled into a flat disk of orbiting ice and rock.

Gravitational waves are ripples in spacetime produced when massive objects accelerate, such as two black holes spiraling together. They stretch and squeeze space itself as they travel outward at the speed of light.

The universe expands because space itself stretches between galaxies, carrying them apart like raisins in rising bread. Distant galaxies recede faster, following the Hubble-Lemaître law, not because they move through space but because more space is being created between them.

Astronomers find exoplanets by detecting the tiny effects these planets have on their host stars, such as a slight dimming when a planet crosses in front or a wobble caused by the planet's gravity. These indirect signals, measured with telescopes, reveal the planet's presence and some of its properties.

A space telescope is a telescope placed above Earth's atmosphere, so its mirrors collect light from distant objects without the blurring and blocking that air causes. It then sends the data to Earth as radio signals, where computers turn it into images and spectra.

A radio telescope captures radio waves emitted by celestial objects using a large dish that reflects and focuses the waves onto a receiver. The receiver amplifies and digitizes the signals, which are then processed by computers to produce images or spectra of the source.

The International Space Station stays in orbit because it moves sideways fast enough that, as gravity pulls it toward Earth, the curve of the planet falls away beneath it at the same rate. It is essentially in continuous free fall, circling Earth roughly every 90 minutes.

A spacesuit works by wrapping an astronaut in a flexible, pressurized bubble that supplies oxygen, removes carbon dioxide and moisture, and keeps temperature and pressure at levels the body can survive. Layers of insulation, cooling tubes and shielding handle the vacuum, radiation and extreme temperatures outside.

Weightlessness in orbit happens because astronauts and their spacecraft are in continuous free fall around Earth, accelerating toward the planet at the same rate. This shared falling removes the normal contact forces that create the sensation of weight.

A spacecraft survives re-entry by using a heat shield to absorb and radiate away the extreme heat generated as it slams into the atmosphere at hypersonic speed. The shield is made of materials that char, melt, or conduct heat away, protecting the vehicle and crew inside.

Reusable rockets land by firing their engines to slow down, then deploying grid fins and landing legs for a controlled touchdown. This allows the booster to be recovered and flown again, cutting launch costs.

Mars rovers work by moving across the surface on wheels, powered by solar panels or nuclear batteries, and controlled by commands from Earth. They carry cameras and instruments to study rocks and soil, sending data back to scientists who plan the next day's driving and experiments.

A satellite stays in orbit because its sideways speed is high enough that, as gravity pulls it downward, the curved surface of the Earth falls away beneath it at the same rate. It is continuously falling toward Earth but moving sideways fast enough to keep missing it.

Day and night happen because Earth spins on its axis, so any given place turns to face the Sun and then away from it. The side facing the Sun has daylight, while the side turned away sits in darkness.

Time zones work by dividing the world into regions that share the same clock time, based on the Earth's rotation and the need for a common local time. Each zone is roughly 15 degrees of longitude wide, corresponding to one hour of the 24-hour day.

A leap year has 366 days instead of 365 because Earth's orbit around the Sun takes about 365.24 days. Adding an extra day every four years keeps the calendar aligned with the seasons.

Venus is so hot because its thick carbon dioxide atmosphere traps heat in a runaway greenhouse effect, keeping the surface near 465°C (about 870°F). Sunlight passes through the clouds, heats the ground, and the resulting infrared radiation cannot escape back to space.

Mars is red because its surface is covered in iron oxide dust, the same rust that forms on iron. Billions of years ago, liquid water and oxygen reacted with iron in the rocks, creating this reddish mineral.

The Moon rotates on its axis in the same time it takes to orbit Earth, so the same hemisphere always faces us. This synchronous rotation, called tidal locking, was caused by Earth's gravity slowing the Moon's spin early in its history.

Stars twinkle because their light passes through moving layers of Earth's atmosphere, which bend the light in shifting directions. This makes the star's apparent position and brightness flicker, while planets usually shine more steadily.

An atomic clock keeps time by locking an electronic oscillator to the exact frequency at which atoms transition between two energy states. Because that frequency is fixed by quantum mechanics and identical everywhere, the clock drifts by less than a second over millions of years.

Weather satellites work by carrying sensors that measure radiation from Earth's surface, oceans and atmosphere, then radioing those measurements to ground stations. Computers turn the data into the cloud images, temperature maps and storm tracks used in daily forecasts.

The universe is everything that exists — all of space, time, matter, and energy, from the tiniest particle to the largest galaxy. It began about 13.8 billion years ago in the Big Bang and has been expanding ever since.

The solar system is the Sun and everything bound to it by gravity — eight planets, their moons, dwarf planets, asteroids, and comets. It formed about 4.6 billion years ago from a collapsing cloud of gas and dust.

The Big Bang is the leading explanation for how the universe began — expanding from an extremely hot, dense state about 13.8 billion years ago and cooling into the galaxies, stars, and planets we see today.

A galaxy is a vast collection of stars, gas, dust, and dark matter bound together by gravity. Our Sun is one of hundreds of billions of stars in the Milky Way galaxy, and the universe contains hundreds of billions of galaxies.

A light-year is the distance light travels in one year — about 9.5 trillion kilometers. Despite the word 'year,' it measures distance, not time, and it's used because cosmic distances are far too vast for everyday units.

A black hole is a region of space where gravity is so strong that nothing — not even light — can escape once it crosses the boundary called the event horizon. They form when massive stars collapse at the end of their lives.

A neutron star is the ultra-dense, collapsed core left behind when a massive star explodes as a supernova. Gravity crushes its protons and electrons together into neutrons, packing more than the Sun's mass into a city-sized sphere.

Dark matter is an invisible form of matter that doesn't emit or reflect light but makes up about 27% of the universe. We know it exists because its gravity holds galaxies together and bends light, even though we can't see it directly.

Dark energy is a mysterious force thought to make up most of the universe and to be driving its expansion to accelerate. We can't see or directly detect it, but its effect — pushing galaxies apart ever faster — is measurable across the cosmos.

A constellation is a recognizable pattern of stars in the night sky that humans have named — like Orion or the Big Dipper. The stars only appear grouped from Earth; in reality they're often vast distances apart.

The Moon is Earth's only natural satellite — a large rocky world that orbits our planet. It has no light of its own; it shines by reflecting sunlight, and its gravity is the main cause of the ocean tides.

A planet is a large, round object that orbits a star, is massive enough for its gravity to pull it into a sphere, and has cleared its orbit of other debris. Earth is a planet, and eight planets orbit our Sun.

An asteroid is a rocky leftover from the early solar system, too small to be a planet. Most orbit the Sun in a belt between Mars and Jupiter, ranging from tiny boulders to bodies hundreds of kilometers across.

A meteor is the streak of light you see when a small space rock burns up in Earth's atmosphere — a 'shooting star.' Friction with the air heats it white-hot in seconds. If any survives to land, it's called a meteorite.

Redshift is the stretching of light to longer, redder wavelengths when its source moves away from you. Because distant galaxies race away as the universe expands, their light is redshifted — which is how we know the cosmos is growing.