Space

Stars are massive balls of hot gas that produce light and heat through nuclear fusion. Our sun is a medium-sized star that provides the energy needed for life on Earth.

Galaxies are enormous collections of stars, gas, and dust held together by gravity. Our Milky Way galaxy contains hundreds of billions of stars and is a spiral galaxy.

Asteroids are rocky objects orbiting the sun, mostly found in the asteroid belt between Mars and Jupiter. Comets are icy objects that develop tails when they approach the sun.

The International Space Station orbits Earth about 400 kilometers above the surface. Astronauts conduct scientific experiments in microgravity conditions there.

Gravity keeps planets in orbit around the sun and moons in orbit around planets. The strength of gravity depends on mass and distance between objects.

Mars is called the Red Planet because iron oxide (rust) covers its surface. Scientists send rovers to Mars to search for evidence of past water and possible microbial life.

The moon's gravity pulls on Earth's oceans, causing the water to bulge and create high and low tides. Most coastlines experience two high tides and two low tides during each day.

Telescopes collect and focus light to make distant objects in space appear larger and brighter. Space telescopes like Hubble orbit above Earth's atmosphere, giving astronomers a clearer view of the universe.

Earth is actually closest to the Sun in early January. Seasons come from the 23.5° axial tilt: the hemisphere tilted towards the Sun receives sunlight at a steeper angle and for more hours, and so warms up.

Planet diagrams almost never show true distances. If the Sun were a football, Earth would be a peppercorn about 26 metres away and Neptune would be nearly 800 metres off. Space is mostly empty, and diagrams that fit on a page hide that.

The Moon rotates once per orbit, so the same hemisphere always faces Earth — tidal locking. There is no permanently dark side: the far side gets just as much sunlight, we simply never see it from here.

Tens of thousands of trackable fragments now orbit Earth at speeds near 8 km/s, where even a paint fleck can hole a spacecraft. Every launch has to plan around them, and collisions create more debris, which is why the problem compounds.