In astronomy and common usage, space is the part of the universelying outside of the limits of the Earth's atmosphere; the apparently empty parts of the Universe, between planetsand stars; the expanse in which the Solar System, stars, and galaxies exist.

Space is not really empty, but the material in space is so dilute that it is hard to detect it. It contains magnetic fields, electromagnetic radiation, gases, dust and other particles. It is sometimes called "outer space" to distinguish it from airspace and terrestrial locations.

As Earth's atmosphere has no abrupt cut-off, but rather thins gradually with increasing altitude, there is no definite boundary between the atmosphere and space. In the United States, persons who travel above an altitude of 50 miles (80 kilometers) are designated as astronauts. 400,000 feet (75 miles or 120 kilometers) marks the boundary where atmospheric effects become noticeable during re-entry. The altitude of 100 kilometers or 62 miles is also frequently used as the boundary between atmosphere and space.

Astronaut   Buzz Aldrin On Moon An astronaut is a person who travels into space, or who makes a career of doing so. The first astronaut was Yuri Gagarin, who was launched into space in April 1961 aboard Vostok 1. The first woman astronaut was Valentina Tereshkova, who was launched into space in June 1963 aboard Vostok 6.	Astronomy   Orion Nebula Astronomy is the sciencedealing with all the celestial objects in the universe, including the planetsand their satellites (e.g. our Earth and the moon), comets and meteors, the stars (including our sun), and interstellar matter, the star systems known as galaxies, and clusters of galaxies.	Space Exploration   NASA - International Space Station Space Exploration is the science and engineering of spacecraft and space probes used for investigation of physical conditions in space and in celestial bodies - e.g. stars, planetsand their moons. Space exploration, or astronautics, is interdisciplinary in that it draws upon the findings of such fields as physics, astronomy, mathematics, chemistry, biology, medicine, electronics, and meteorology.
Galaxies   You Are Here A galaxy is a massive ensemble of stars, dust, and gas, all gravitationally interacting, and orbiting about a common center. The Sun is one of the billions of stars in our Galaxy, one of billions of galaxies in the Universe. All the stars visible to the unaided eye from earth belong to the earth's galaxy, the Milky Way. The sun with its associated planets is just one star in this galaxy.	The Hubble Space Telescope   Hubble Rescue HST - a joint ESA/NASA project - is a 2.4-meter reflecting telescope which was deployed in low-Earth orbit (600 kilometers) by the crew of the space shuttle Discovery (STS-31) on 25 April 1990. It is a long-term spacebased observatory. The observations are carried out in visible, infrared and ultraviolet light. During its years of operation HST has managed to become one of the most important science projects ever. HST has enabled scientists to make many astronomical discoveries, including the first observations of a black hole.	NASA October 1, 1958, the official start of the National Aeronautics and Space Administration (NASA), was the beginning of a rich history of unique scientific and technological achievements in human space flight, aeronautics, space science, and space applications. Formed as a result of the Sputnik crisis of confidence, NASA inherited the earlier National Advisory Committee for Aeronautics (NACA), and other government organizations, and almost immediately began working on options for human space flight.
Solar System Planets   Our Solar System Our Earth is one of 9 planetsorbiting the Sun. The planets are vast balls of rock, metals, and gases that orbit a star. Other stars may have planets too. A planet is a celestial object which revolves around a star and reflects that star's light. Nine planets have been discovered in our solar system. Mercury, Venus, Earth, and Mars are the planets closest to the Sun. They are called the inner planets. The inner planets are made up mostly of rock. The outer planets are Jupiter, Saturn, Uranus, Neptune, and Pluto. Jupiter, Saturn, Uranus, and Neptune are large balls of gases with rings around them. Pluto is the farthest planet from the Sun. It is coated with ice.	SETI   Extraterrestrial SETI (Search for Extraterrestrial Intelligence) is an attempt to detect technological civilizations elsewhere in the universe, particularly in our galaxy. Billions of places outside our solar system may host life, that we could discover, if it has developed to a technological level at least as advanced as our own.	Space Shuttle   Endeavour on Pad The Space Shuttle is a reusable rocket-launched vehicle designed to transport people and cargo between Earth and orbiting spacecraft, and then to return to the Earth's surface by gliding down and landing on a runway. A Space Shuttle consists of a reusable delta-winged spaceplane, called an orbiter; two solid-propellant booster rockets, which are recovered and also reused; and an expendable tank containing liquid propellant for the orbiter.s three main engines. Only the orbiters have names, and an orbiter alone is not a full Space Shuttle.
Stars   Hoag's Object On a really dark night, you can see about 1000 to 1500 stars. Trying to tell which is which is hard. The constellations help by breaking up the sky into more managable bits. They are used as mnemonics, or memory aids. For example, if you spot three bright stars in a row in the winter evening, you might realize that you are seeing "Orion's Belt". Then you begin to recognise the rest of Orion: There's Betelgeuse in Orion's left shoulder and Rigel is his foot. And once you recognize Orion, you can remember that Orion's Hunting Dogs are always nearby.	Sun   Solar Flares The night sky is full of stars, so distant they are mere points of light. The sun is a star that, by the gravitational effects of its mass, dominates the planetary system that includes the earth, and we are much closer to it than to any other star. Along with the other planets, the Earth orbits the Sun. The Sun is a ball of glowing gases, three quarters hydrogen and one quarter helium, with traces of other elements.	Universe   Eagle Nebula In astronomy, the universeis everything there is that can be detected by physical effects; the aggregate of all matter, energy and space. It includes the planets, Earth, Sun, Stars, and Galaxies. The Universe is thought to be 15 billion years old. It started with a huge explosion called the Big Bang. The Universe is expanding - all the galaxies are flying away from each other, like spots on a balloon being blown up.