Page 5 - Curriculum Visions Dynamic Book

To us the Earth is huge. It is 6,378 km to the center, and
it takes 40,000 km to make one complete circuit around the edge—a distance that takes over a day to cover even on modern passenger jet planes.
In the past, when people could only travel slowly, the Earth must have seemed boundless. Yet, seen on the scale of the planets around us in our solar system, the Earth is just a small rocky planet accompanied by another orbiting planetlike body that we call the Moon.
Earth and Moon: close but different
The Moon, which is a satellite of the Earth, is large as moons go. It is very close to us, just 384,000 km away. But
the contrast between the Earth and the Moon could not
be greater. The Moon is a geologically dead world with the thinnest of atmospheres. It supports no life. It does not change. The Earth, on the other hand, is certainly unique within the Solar System and possibly elsewhere too, because it is geologically active, it has an atmosphere with free oxygen, and its surface contains free carbon that forms the basis of life. As a result, the Earth is constantly changing, both within and on the surface. It is also able to support nearly seven billion people and countless billions of other living things.
A speck in the cosmic ocean
Science has helped people change their belief that the Earth is the center of the Universe to realizing it is only a speck in the cosmos.
We now know that the Earth is just a small planet orbiting a small star in one galaxy among the vastness of space. But none of this has lessened the interest that we have in our own Earth and its Moon.
 This view from the Apollo 11 spacecraft shows the Earth rising above the Moon’s horizon.
For more on our Solar System see Volume 2: Sun and
Solar System.
apollo The program developed in the United States by NASA to get people to the Moon’s surface and back safely.
atmosphere The envelope of gases that surrounds the Earth and other bodies in the Universe.
cosmos The Universe and everything in it. The word “cosmos” suggests that the Universe operates according to orderly principles.
earth The third planet from the Sun and the one on which we live.
galaxy A system of stars and interstellar matter within the Universe.
moon The natural satellite that orbits the Earth.
planet Any of the large bodies that orbit the Sun.
satellite An object that is in an orbit around another object, usually a planet.
solar system The Sun and the bodies orbiting around it.
space Everything beyond the Earth’s atmosphere.
star A large ball of gases that radiates light. The star nearest the Earth is the Sun.
Universe The entirety of everything there is; the cosmos.
To find out more about our galaxy, see Volume 1: How the Universe works.
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