Start here · Essential guide
A Brief History of Space Exploration
A plain-language timeline of space exploration, from the first satellites and crewed flights to Moon landings, space stations, rovers and deep-space probes.
Universe and Matter
Planets and Space Exploration
Missions, the Moon, eclipses and the search for life beyond Earth.
Could There Be Life Elsewhere in the Universe?
What scientists know and do not know about life beyond Earth: how they search, which places look promising, and where evidence ends and speculation begins.
How Rockets Reach Orbit
Why getting to orbit is mostly about sideways speed, and how thrust, staging and fuel let a rocket reach roughly 28,000 kilometers per hour.
How Solar and Lunar Eclipses Happen
Eclipses happen when the Sun, Earth and Moon line up. Learn the difference between solar and lunar eclipses and why they do not occur every month.
How Space Telescopes See the Distant Past
Light takes time to travel, so far-away objects are seen as they were long ago. Learn why astronomers launch telescopes above Earth's atmosphere.
The Apollo Moon Landings Explained
What NASA's Apollo program did between 1961 and 1972, how the six crewed Moon landings worked, and the independent evidence showing they really happened.
What Daily Life Is Like on the International Space Station
How astronauts sleep, eat, exercise, wash and work in microgravity aboard the International Space Station, and why the lab orbits Earth every 90 minutes.
Why Mars Is a Favorite Target for Exploration
Why Mars gets so many rovers and orbiters: its past water, Earth-like days and seasons, reachable distance, and what missions are learning about the planet.
Why Pluto Is Called a Dwarf Planet
In 2006 astronomers defined what a planet is, and Pluto did not fit all three criteria. Learn the definition, the reasoning and the debate that continues.
Why the Moon Has Phases
The Moon's phases come from sunlight and our viewing angle as it orbits Earth each month, not from Earth's shadow. See the cycle explained step by step.
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Our Universe Space, the solar system and how we picture the cosmos. Physics and Matter Modern physics, light, the elements and everyday math. Stars and Galaxies How stars live and die and how galaxies and the early universe are understood. Forces, Energy and Motion Classical physics that explains everyday motion, heat, sound and electricity. Chemistry and Materials Reactions, everyday substances and how common materials are made.