NASA, in partnership with other U.S. and international agencies, has been studying Earth as an integrated system. Viewing Earth from the unique perspective of space provides the opportunity to see Earth as a whole. Scientists around the world have discovered many things about our planet by working together and sharing their findings.

Some facts are well known. For instance, Earth is the third planet from the Sun, and the fifth largest in the solar system. Earth's diameter is just a few hundred kilometers larger than that of Venus. Our planet rotates on its axis at a surface speed of approximately 0.5.km/sec at mid-latitudes, while orbiting the Sun at a speed about 30 km/sec. We experience these motions as the daily routine of sunrise and sunset and the slower change of the seasons. The four seasons are a result of Earth's axis of rotation being tilted more that 23 degrees.

The changing nature of the planet's systems are the mysteries that scientists study today. For instance, the North American continent continues to move west over the Pacific Ocean basin, roughly at a rate equal to the growth of our fingernails. We are made aware of this movement when it is interrupted by earthquakes. Scientists notice a distinctive pattern to those earthquakes, leading them to conclude that Earth is dynamic, with its spherical surface separated into moving caps or plates. Earthquakes result when plates grind past one another, ride up over one another, collide to make mountains, or split and separate. These movements are known as plate tectonics. Developed within the last thirty years, this explanation has unified the results of centuries of study of our planet, long believed to be unmoving.

Oceans at least 4 km deep cover nearly 70% of Earth's surface. Water exists in the liquid phase only within a narrow temperature span (0 degrees to 100 degrees C). This temperature span is especially narrow when contrasted with the full range of temperatures found within the solar system. The presence and distribution of water vapor in the atmosphere is responsible for much of the Earth's weather.

On the surface, we are enveloped by an ocean of air that consists of 78% nitrogen, 21% oxygen, and 1% other ingredients. Earth's atmosphere shields us from nearly all harmful radiation coming from the Sun, and protects us from meteors as well-most of which burn up before they can strike the surface. Satellites have revealed that the upper atmosphere, which was thought to be calm and uneventful, actually swells by day and contracts by night due to solar activity. The upper atmosphere contributes to Earth's weather and climate and protects us from the Sun's harmful ultraviolet radiation.

Besides affecting Earth's weather, solar activity gives rise to a dramatic visual phenomenon in our atmosphere. When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and are known as the auroras, or the Northern and Southern lights.

Our planet's rapid spin and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape. The solar wind is a stream of charged particles continuously ejected from the Sun. The magnetic field does not fade off into space but has definite boundaries.