Earth from Space

This is our home, surrounded by the blackness of space.

Earth is a tiny speck in a very vast universe. It is about 8000 miles across. It lies 93 million miles from the Sun, and nearly 20 quadrillion miles from the next-nearest star. Light travels from the Sun to the Earth in about 8 minutes; it would take light 3 years to travel from the Sun to the nearest star. The fastest spacecraft that humans have ever launched, New Horizons, travels at 51,000 miles per hour (23 km/s), and would take 50,000 years to reach the nearest star.

By weight, our Earth is also a tiny spec. It would take 300,000 Earths to equal the mass of the Sun. Our Sun is just one of between 200 and 400 billion stars in the Galaxy. Many of these stars are smaller than the Sun, so that the total mass of the Galaxy is about 20 billions times that of the Sun. In the visible universe there are several trillion other galaxies.

Our time on the Earth has been vanishingly short. Humans have been on it for a few hundred thousand years, at most. Multi-celled life has been on Earth a bit longer, about 500 million years since the Cambrian explosion. By studying radioactive elements in the Earth's crust, we have found that the Earth is about 5 billion years old. By studying the oldest stars in the Universe, and by tracing its expansion since the Big Bang, we find that the Universe is about 13 billion years old.

The material that makes up the Earth did not exist in its current form when the universe was formed. The hydrogen, helium, and lithium within this blue-green ball was produced in the Big Bang. Helium and lithium are rare on Earth. The hydrogen is most prominent in the water that covers three-quarters of the Earth's surface. The rest of the Earth's surface is a mixture of carbon, silicon, iron, and other elements that emerge at their high points above the water. These elements were produced in the core of a star, ejected into space during a supernova explosion, and incorporated into the Earth and its Sun when an interstellar cloud collapsed. Make enough carbon, silicon, and iron required several generations of stars to form and eventually end their lives --- Earth couldn't have formed much earlier than it did.

If you look out into space, this may make us seem lonely. However, there are 6 billion of us to share this speck of space dust. Aside from a lucky few of us that might get to take an interplanetary journey in the future (can you imagine sending more than, say 1000 people on a 10,000 year journey to another star?), this is where we are going to be our entire lives. This is where future generations will live. We seem alone when you look up into space, but here on Earth, we are all in this together.