1 The Earth in Context The geocentric model of the Universe placed the Earth at the center of the Universe. The heliocentric model placed the Sun at the center.
The Earth is one of the eight planets orbiting the Sun.This Solar System lies on the outer edge of the Milky Way galaxy. The Universe contains hundreds of billions of galaxies.
The red shift of light distant galaxies led to the expanding Universe theory.
by Eric Hughes 作者:埃里克·休斯 Privacy is necessary for an open society in the electronic age. Privacy is not secrecy. A private matter is something one doesn’t want the whole world to know, but a secret matter is something one doesn’t want anybody to know. Privacy is the power to selectively reveal oneself to the world. 在电子时代,隐