2010年12月21日发生月食,当天月球上中天时刻为夜半..为什么

解题思路：光在同一均匀介质中是沿直线传播的，应用的实例有：日食、月食、射击时的瞄准要领是“三点一线”．

日食是当月球位于太阳与地球之间，三者在同一条直线上时，不透明的月球挡住了沿直线传播的太阳光，在地球上看不到太阳的现象．
故答案为：直线传播．

点评：
本题考点： 光直线传播的应用．

考点点评： 本题考查了日食的形成原因，知道日食是光沿直线传播形成的，知道发生日食时，太阳、地球、月球间的位置关系，是解题的关键．

As is known to all, high school students in China have been overloaded with academic pressure. They have to study over 12 hours a day in school, even attending extra classes on most of weekends and national holidays, which greatly affects students’ health both physically and psychologically.
To help solve this problem, last December, Hunan Provincial Education Department proclaimed a strict ban to make sure that no high school students, even those in Senior 3, shall go to school on weekends or during official holidays. This means students can enjoy more relaxing holidays. But most parents, especially those with graduating children, are quite worried about their kids’ grades.
As a Senior 3 student myself, I warmly welcome this ban. While enjoying the coming longer winter vacation, I will also try to make full use of every minute to study more efficiently. Besides, with a tighter schedule, teachers will try to seek a better approach to teach more effectively, which, I think, can benefit us students a lot. So let’s hope this ban will come into effect eventually.

2010年 12月21日 星期二822天前
21
农历 冬月十六
庚寅年 【虎年】 戊子月 乙巳日

不会..地球在一个很平稳的宇宙环境中...

1、B
2、C

楼主是想看月全食吧,刚刚用软件Stellarium模拟了一下,按坐标（N24°29′,E118°05′）模拟的结果月出时间是17点27分,这时天还没黑,月亮已经开始复原了差不多一半,等到6点月亮完全复原时高度也不到7度,观看条件比较差.楼主想看的话可以找个开阔的地方,东边最好不要有建筑物遮挡,也不要抱太大期望.