Outer space is the vast emptiness that exists beyond Earth's atmosphere, where planets, stars, and galaxies move in an almost perfect vacuum. When astronauts travel more than about 60 miles above Earth's surface, they enter outer space, where there's no air to breathe, no weather, and almost no sound.

In outer space, temperatures swing wildly: objects in direct sunlight can heat up to hundreds of degrees, while objects in shadow plunge to hundreds of degrees below zero. Without air pressure, many liquids can boil away quickly, and humans can't survive without spacesuits.

Despite being called “empty,” outer space isn't completely nothing. Tiny particles of dust, stray atoms of hydrogen, and invisible forces like gravity and radiation drift through it. Light travels through outer space from distant stars, taking years or even millions of years to reach our eyes.

Humans have explored outer space since 1961, when Yuri Gagarin became the first person to orbit Earth. Today, astronauts live and work on the International Space Station, orbiting in outer space while conducting experiments impossible to perform on the ground. The exploration of outer space represents one of humanity's grandest adventures, pushing the boundaries of what's possible.