Our universe

Earth, our home, is a small blue planet floating in the vast expanse of space. It's where all of human history has taken place—every person who has ever lived and every story that has ever been told. This is where our cosmic journey begins.

As we move beyond Earth’s atmosphere, past the Moon and the Sun, we begin to grasp the immense scale of the universe. The first major landmark is the Moon, located about 384,000 kilometers from Earth. To put that into perspective, driving there non-stop at 100 km/h would take over 160 days. From the Moon, Earth looks like a delicate sphere of blue and green suspended in the blackness of space—a view that offers a powerful sense of perspective.

Next on our journey is the Sun, about 150 million kilometers from Earth, a distance known as one astronomical unit i.e.AU. Even light, which travels at 300,000 km/s, takes around 8 minutes and 20 seconds to reach us from the Sun. A commercial jet flying at 900 km/h would take about 19 years to make the trip. Despite the distance, the Sun powers life on Earth with its energy.

Moving further, we reach Mars, our neighboring planet. At its closest, Mars is 54.6 million kilometers away, but this can stretch to 401 million kilometers depending on the planets' positions. Traveling there by jet could take more than 50 years. This vast separation is one reason why sending spacecraft to Mars is such a challenge—distances and orbital timing must be carefully calculated.

Continuing outward, we encounter Neptune, an icy giant located roughly 4.5 billion kilometers from Earth. Sunlight takes about 4 hours and 15 minutes to reach it. This gives a sense of just how enormous our solar system really is. Beyond Neptune lies Voyager 1, a spacecraft launched in 1977. Now over 22 billion kilometers away, it’s the most distant human-made object. In 1990, Voyager 1 turned its camera back toward Earth, capturing the famous “Pale Blue Dot” image, a tiny point in the vastness of space that reminds us of our responsibility to care for our fragile home.

At the edge of the solar system is the Oort Cloud, a theoretical shell of icy bodies extending up to 100,000 AU—or about 1.9 light-years—from the Sun. This marks the beginning of interstellar space. The boundary, called the heliopause, is where the Sun’s influence ends and the greater galaxy begins.

Beyond the solar system lies Alpha Centauri, the closest star system to us, about 4.4 light-years away—or over 41 trillion kilometers. At our current speeds, even the fastest spacecraft would take more than 70,000 years to reach it. These vast distances highlight the challenge of interstellar travel.

Zooming out further, we come to the Milky Way galaxy, our cosmic home. It spans about 100,000 light-years and contains hundreds of billions of stars. Within this galaxy lies a small area known as the human “radio bubble,” about 100 light-years across. This is the farthest our radio signals have traveled, meaning most of the galaxy hasn’t yet heard from us.

Beyond the Milky Way lies intergalactic space, an immense void where galaxies are scattered like islands. Our galaxy is part of a small cluster called the Local Group, which contains more than 50 galaxies and stretches across 10 million light-years. Light would take 10 million years to travel from one end to the other.

Expanding further, we reach the Virgo Supercluster, which contains our Local Group and thousands of other galaxies, spanning about 110 million light-years. And even this vast structure is part of an even larger one—the Laniakea Supercluster, a name meaning “immense heaven” in Hawaiian. It stretches over 500 million light-years and includes the mysterious "Great Attractor," a region exerting a strong gravitational pull on galaxies, including our own.

Finally, we arrive at the edge of the observable universe, which spans about 93 billion light-years. This may seem surprising given the universe is only 13.8 billion years old, but cosmic expansion explains this apparent contradiction. Space itself has been stretching since the Big Bang, pushing galaxies away from us. Some are moving so fast that their light will never reach us, making them forever invisible.

In the end, the observable universe may be just a small portion of the true cosmos. There could be countless galaxies, stars, and phenomena beyond our reach—wonders we may never witness, forever beyond the limits of our view.

Black holes come in two main types: stellar-mass black holes and supermassive black holes.

Supermassive black holes earn their name by containing masses that range from millions to billions of times greater than that of our Sun.

Evidence suggests that nearly every galaxy in the universe harbors a supermassive black hole at its core—like a central seed. Interestingly, there appears to be a correlation between the size of a galaxy and the mass of its central black hole: larger galaxies tend to host larger black holes, and smaller galaxies, smaller ones. This link leads scientists to believe that supermassive black holes may play a key role in galaxy formation. However, the exact nature of this relationship—and how these enormous black holes formed in the first place—remains unknown.

The supermassive black hole in our own galactic neighborhood sits at the center of the Milky Way. It’s known as Sagittarius A* (pronounced “A-star”). Measuring roughly 15 million miles across, it holds a mass equivalent to about 4 million Suns. Fortunately, it’s far enough from Earth that it poses no threat to us.