How Far Is Outer Space from Earth? Closer Than You Think

Outer space is generally considered to begin at the Karman line, approximately 100 kilometres (62 miles) above the Earth's surface.

Outer space is the vast expanse that exists beyond the Earth's atmosphere, including the regions between celestial bodies.

When we look up at the night sky, it appears to be filled with stars and other celestial objects. However, in reality, almost all of that immense area we call the universe is made up of space, a near-perfect vacuum.

Sound waves require air, liquids or solids to travel through; therefore, space is an extremely silent place, as sound cannot travel through a vacuum. Even if two astronauts were floating close together outside their spacecraft, they would not be able to hear each other. Their voices need a material through which to travel, and space simply does not provide one.

Pinpointing the exact boundary where space begins is challenging. However, most scientists agree on the Karman line, an imaginary boundary located about 100 kilometres (62 miles) above sea level, as the conventional beginning of outer space. At this height, the atmosphere has become so thin that conventional aircraft can no longer generate enough lift to remain in flight.

Most of the Earth's atmosphere lies below the Karman line, although an extremely thin atmosphere continues above it. The farther you travel from the Earth's surface, the thinner the atmosphere becomes until it gradually merges with outer space.

Even the emptiest regions of the Universe contain a few atoms per cubic metre (35 cubic feet), and space is also filled with various forms of radiation, including visible light, radio waves, X-rays and cosmic rays. So, although we often describe space as empty, it is not completely devoid of matter or energy.

The International Space Station (ISS) orbits the Earth at an altitude of about 400 kilometres (250 miles), although this varies slightly over time. Artificial satellites can orbit much closer to Earth or much farther away than the ISS, depending on their purpose. Some provide communications, some help us navigate using GPS, and others monitor the Earth's weather and climate.

The average maximum cruising altitude for commercial aircraft is around 13 kilometres (8 miles); any higher, and the atmosphere becomes too thin to support large passenger aircraft. This means that astronauts aboard the ISS are orbiting more than 30 times higher than a typical airliner.

Yuri Gagarin, a Soviet pilot, was the first human to enter space in April 1961. Since then, well over 700 people have made the journey into space. Although space travel has become more common in recent years, it is still one of the rarest experiences a human being can have.

That is a remarkably small number of people, considering that an estimated 117 billion humans have lived throughout history, with approximately 8 billion still alive today.

The size of outer space is truly beyond comprehension. Modern telescopes can observe galaxies whose light has travelled for more than 13 billion years before reaching Earth. That light has been travelling through space at approximately 1.08 billion kilometres per hour (671 million miles per hour), the speed of light, for all of that time.

The universe continues to expand, and observations show that this expansion is accelerating. Scientists estimate that the observable universe is about 93 billion light-years in diameter. Beyond that lies even more of the universe, although we cannot yet observe it because its light has not had enough time to reach us.

In one year, light travels approximately 9.46 trillion kilometres (5.88 trillion miles). A trillion is 1 followed by twelve zeros.

Now multiply 9.46 trillion kilometres (5.88 trillion miles) by 93 billion, and that gives you some idea of the unimaginable size of the observable universe.

The numbers become so enormous that they are almost impossible for the human mind to visualise.

British spelling.

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