Mercury， with the angle never more than 28°from the Sun， is a planet closest to the Sun. Mercury moves quickly along a section of strange curves in one and a half months， appearing and disappearing mysteriously. At this time， it moves from the most eastern to the most western with an average speed of 47.89 km/s. Mercury is the fastest planet in the solar system.
The track that Mercury moves around the sun is relatively flat oval. When it moves to the perihelion① or the aphelion②， the size of the Sun may be poor or doubled. The Sun moves slowly in the sky of Mercury. It takes you a few hours to see sunrise. You can observe the coronal③ sun and color ball carefully for a long time. However， it is impossible to go to Mercury. The distance between Mercury and the sun is three times longer than the distance between the earth and the sun. In addition， there is no atmosphere， so the sunlight in Mercury is even six stronger than in the equator④. As a result， metals with low melting point will be melted， let alone human being.
Mercury’s surface is similar to the moon. Large or small craters⑤ such as mountains and plains and the hanging shore cliffs and so on spread all over the surface.
Mercury rotates when in the revolution⑥ around the sun. In 1965， an astronomer in the United States measured the rotation period of Mercury (58.646 days， which is 2/3 longer than rotating around the Sun.) successfully. It is one day and night if the earth rotates once， while it will be one day and night until it rotates three times. One day and night in Mercury is equivalent to 176 days in the earth. At the same time， Mercury just also rotates twice. Therefore， one day in Mercury equals to two years in the earth. Mercury in the perihelion is always toward the sun with the same longitude， and there is a far point of 90° when Mercury is toward the sun in the aphelion at the same longitude⑦， which there are seasonal changes with a longitude in Mercury.
① perihelionn. ［天］近日点
② aphelionn. ［天］远日点
③ coronaladj. ［天］日冕的
④ equatorn. 赤道［the S］
⑤ cratern. (月环表面的)环形山［C］
⑥ revolutionn. (天体的)运行 、公转
⑦ longituden. 经度［U］［C］
水星
水星是最靠近太阳的行星，它与太阳的角距从不超过28°，水星行动迅速，神出鬼没，在一个半月的时间里它会沿着一段奇特的曲线，从太阳的最东边跑到最西边，平均速度为每秒47.89千米，是太阳系中运动最快的行星。
水星绕太阳公转的轨道是个较扁的椭圆，当它在近日点和远日点时，所看到的太阳大小可差一倍多。太阳在水星天空中移动得慢极了，如果在水星上看日出，要耐着性子花上十几个小时。在水星上可以长时间地仔细观察日冕和色球。然而要想到水星上去是不可能的。地球到太阳的距离是水星离太阳的三倍左右，再加上没有大气遮挡，水星上的阳光比地球赤道的阳光还强6倍，不要说人，就是一些熔点较低的金属也会熔化。
水星表面和月球表面极为相似。水星表面大大小小的环形山星罗棋布，既有高山，也有平原，还有令人胆寒的悬岸峭壁。
水星在绕太阳公转的同时，本身也在自转。1965年，美国的一个天文学家成功地测量了水星的自转周期为58.646日，正好是水星公转周期的2／3。地球每自转一周就是一昼夜，而水星自转三周才是一昼夜。水星上一昼夜的时间，相当于地球上的176天。与此同时，水星也正好公转了两周。因此人们说水星上的一天等于地球上的两年。由于水星在近日点时总以同一经度朝着太阳，在远日点时以相差90°的经度朝着太阳，所以水星随着经度不同而出现季节变化。
