Quick Facts
What Is Space?
Space begins where Earth’s atmosphere becomes too thin to support aircraft flight, commonly considered to start at the Kármán line (about 62 miles or 100 km above sea level). Beyond that boundary lies a near-vacuum filled with sparse particles, radiation, magnetic fields, and the gravitational influence of celestial bodies.
On larger scales, space contains planetary systems, stars, nebulae, galaxies, and vast intergalactic voids. It is the setting for all astronomical phenomena and the arena of human space exploration.
The Scale of Space
A distance light travels in about 1.3 seconds.
Light takes about 8 minutes to reach us.
Even the closest star beyond the Sun is enormously distant.
Our home galaxy contains hundreds of billions of stars.
The portion of the universe we can in principle observe.
Major Components of Space
Stars
Massive spheres of plasma held by gravity, generating energy through nuclear fusion. They are the basic building blocks of galaxies.
Planets & Moons
Bodies that orbit stars (or planets). Our solar system includes rocky planets, gas giants, ice giants, and many natural satellites.
Nebulae
Clouds of gas and dust that can be the birthplaces of stars or the remnants of stellar explosions.
Galaxies
Vast systems of stars, gas, dust, and dark matter bound by gravity. The Milky Way is one of hundreds of billions.
Human Exploration of Space
Since the late 1950s, humans have sent probes, satellites, landers, and crewed spacecraft beyond Earth. Milestones include the first satellites, human orbital flight, the Moon landings, robotic exploration of the solar system, space stations, and ongoing missions to Mars and beyond.
Space exploration advances scientific knowledge, drives technological innovation, and expands the range of human activity. It also raises practical questions about life support, propulsion, radiation protection, and long-duration missions.
Why Space Matters
Scientific Understanding
Studying space reveals how stars, planets, and galaxies form and evolve, and how the universe began and develops.
Practical Technology
Satellites enable communication, navigation, weather forecasting, and Earth observation that support modern life.
Perspective
Seeing Earth from space highlights both the fragility and the uniqueness of our planet within the wider cosmos.
The Final Frontier
Space is the immense environment that surrounds our planet and contains everything else in the universe. From the nearby Moon to distant galaxies, it offers both profound scientific questions and practical opportunities.
Understanding space begins with grasping its scale, its major components, and the ongoing human effort to explore and use it. The more we learn, the clearer our place in the cosmos becomes.