Gravity in Space

Gravity in space is the same force that keeps you on the ground, working across huge distances between planets, stars, and galaxies. Gravity is the pull that every object with mass has on every other object. The bigger the mass, the stronger the pull. Space is mostly empty, but gravity fills it. It reaches across trillions of miles and shapes how the whole universe moves.

Gravity is what keeps the solar system together. The Sun is by far the most massive thing nearby. Its gravity holds Earth and the other planets in their orbits. Without the Sun's pull, Earth would fly off in a straight line into deep space. Instead, Earth loops around the Sun once a year, trapped by gravity it cannot see or touch.

The same thing happens closer to home. Earth's gravity holds the Moon in orbit about 239,000 miles away. The Moon's gravity pulls back on Earth. That pull is what causes the ocean tides, lifting the sea higher twice a day.

Many people think there is no gravity in space. That is not true. On the International Space Station, about 250 miles above Earth, gravity is still almost 90 percent as strong as it is on the ground. So why do astronauts float? Because the space station is falling. It moves sideways so fast, about 17,500 miles per hour, that it keeps missing the Earth as it falls. The astronauts inside are falling at the same speed as the station, so they feel weightless. Scientists call this free fall.

Gravity gets stranger the bigger things get. Near a black hole, gravity is so powerful that not even light can escape. Albert Einstein figured out something surprising about this in 1915. He showed that gravity is not just a force pulling on things. It is a bending of space and time itself. A heavy object like the Sun makes a kind of dip in space, and planets roll around inside that dip. Scientists have tested this idea many times, and it keeps turning out to be correct.

There are still big mysteries left. Most of the gravity in the universe seems to come from something called dark matter, a kind of stuff nobody has ever seen. Scientists know it must be there because of how galaxies spin. What it actually is, we do not yet know.