Earth are part of the vast universe, alongside other planets and their numerous moons.

These planets, along with asteroids and comets, orbit the Sun.

The Sun itself is just one of billions of stars in the Milky Way galaxy, most of which are believed to host their own planets, known as exoplanets. The Milky Way is only one of billions of galaxies within the observable universe, and it's thought that nearly every galaxy contains a supermassive black hole at its center.

From the countless stars and galaxies to the unseen matter and energy that make up the cosmos, everything in existence is part of the universe, the all-encompassing whole that we call everything.

Although the universe may seem distant and strange, it’s much closer than we often think. Right now, no matter where you are, outer space is only about 62 miles (100 kilometers) away. Whether you're inside or outside, awake or asleep, eating lunch or drifting off in class, space is always just a few dozen miles above you. About 8,000 miles (12,800 kilometers) beneath your feet, on the other side of the Earth, lies the same harsh vacuum and radiation of outer space.

In fact, you’re technically already in space. We often talk about being out in space, as if Earth is separate from the rest of the universe, but the truth is Earth is a planet in space, just like all the others. The difference is that Earth has conditions that support life, making it a rare and fragile exception in the vastness of the cosmos. For humans and all the other life forms here, nearly the entire universe is an inhospitable, unforgiving environment.

How old is Earth?

Earth, our home, is not only an oasis in space, but also in time. While it may seem permanent to us, the planet is a fleeting presence in the grand history of the universe. For almost two-thirds of the universe’s existence, Earth didn’t even exist.

And it won’t last forever either. In several billion years, the Sun will expand, possibly engulfing Mercury and Venus, and may even reach Earth, though it’s uncertain exactly how it will unfold. Predicting the distant future is tricky, as humanity is just beginning to understand the cosmos.

How old is the universe?

The universe itself is roughly 13.8 billion years old. This estimate comes from measuring the ages of the oldest stars and calculating the rate of expansion of the universe. By observing the Doppler shift in light from distant galaxies, scientists have discovered that nearly all galaxies are moving away from us, and the farther they are, the faster they recede.

Surprisingly, instead of gravity slowing this motion, galaxies are speeding up — and scientists are still unsure why. Eventually, galaxies will be so far away that their light will no longer be visible from Earth.

What is the universe made of?

The universe is composed of all the matter and energy that exist. Much of the observable matter takes the form of hydrogen atoms, the simplest element, made up of just a proton and an electron (or a neutron in some cases, which turns it into deuterium). When atoms bond by sharing electrons, they form molecules.

When many trillions of atoms clump together, they form dust particles. Pack a few tons of carbon, oxygen, silica, ice, and metals together, and you get an asteroid. And if you collect 333,000 Earth masses of hydrogen and helium, you get a star like our Sun.