| If you are travelling in a train, the
things (Example: {{U}}(0) {{/U}}) seem to be {{U}}(41) {{/U}}
backwards. But this is not really true. It is the train that is
moving. It is like the case {{U}}(42) {{/U}} the earth and the sun. The sun seems {{U}}(43) {{/U}} in the east, move across the sky, and set in the {{U}}(44) {{/U}}. In other words, the sun seems to travel round the earth. However, {{U}}(45) {{/U}} not really true. It is the earth that is turning on {{U}}(46) {{/U}} own axis (轴) . The turning of the earth on its own axis is what makes the change {{U}}(47) {{/U}} day to night. The earth also travels round the sun on an unchanging path (路径). As well as the earth, {{U}}(48) {{/U}} other planets(行星) of {{U}}(49) {{/U}} sizes. These are known as the solar system. The planet nearest the sun is Mercury, and the planet {{U}}(50) {{/U}} from the sun is Pluto. |