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Space exploration
What is space?


flying in the space

Space is the near-emptiness in which all objects in the universe move. The planets and the stars are tiny dots compared with the vast expanse of space.

The beginning of space. Earth is surrounded by air, which makes up its atmosphere. As the distance from Earth increases, the air becomes thinner. There is no clear boundary between the atmosphere and outer space. But most experts say that space begins somewhere beyond 60 miles (95 kilometers) above Earth.

Outer space just above the atmosphere is not entirely empty. It contains some particles of air, as well as space dust and occasional chunks of metallic or stony matter called meteoroids. Various kinds of radiation flow freely. Thousands of spacecraft known as artificial satellites have been launched into this region of space.

Earth's magnetic field, the space around the planet in which its magnetism can be observed, extends far out beyond the atmosphere. The magnetic field traps electrically charged particles from outer space, forming zones of radiation called the Van Allen belts.

What is space? The region of space in which Earth's magnetic field controls the motion of charged particles is called the magnetosphere. It is shaped like a teardrop, with the point extending away from the sun. Beyond this region, Earth's magnetic field is overpowered by that of the sun. But even such vast distances are not beyond the reach of Earth's gravity. As far as 1 million miles (1.6 million kilometers) from Earth, this gravity can keep a satellite orbiting the planet instead of flying off into space.

Space between the planets is called interplanetary space. The sun's gravity controls the motion of the planets in this region. That is why the planets orbit the sun.

Huge distances usually separate objects moving through interplanetary space. For example, Earth revolves around the sun at a distance of about 93 million miles (150 million kilometers). Venus moves in an orbit 68 million miles (110 million kilometers) from the sun. Venus is the planet that comes closest to Earth-25 million miles (40 million kilometers) away-whenever it passes directly between Earth and the sun. But this is still 100 times as far away as the moon.

Space between the stars is called interstellar space. Distances in this region are so great that astronomers do not describe them in miles or kilometers. Instead, scientists measure the distance between stars in units called light-years. For example, the nearest star to the sun is Proxima Centauri, 4.2 light-years away. A light-year equals 5.88 trillion miles (9.46 trillion kilometers). This is the distance light travels in one year at its speed of 186,282 miles (299,792 kilometers) per second.

What is space?Various gases, thin clouds of extremely cold dust, and a few escaped comets float between the stars. Interstellar space also contains many objects not yet discovered.

Contributor: James Oberg, M.S., Spaceflight Engineer; author, UFOs and Outer Space Mysteries.
Source : World Book 2005

Space exploration
What is space?
Getting into space and back
Living in space
Meeting basic needs in space
Communicating with Earth
The dawn of the space age
Space probes
Probes to Venus
Probes to Jupiter and beyond
Probes to comets
Human beings enter space
Apollo: Mission to the moon
Exploring the moon
Returning to Earth
The International Space Station
Space shuttles
Types of shuttle missions