Human Activities.
以下的观察均适用于北半球温带地区 (northern temperate zone)；这是大多数古文明发轫的区域，如古巴比伦，古埃及，古希腊与古中国。
Daily Motion of the Sun
太阳的日常运动有三个重要的规律：
- Sunrise and Sunset Timing. The Sun rises earlier until it reaches the earliest sunrise time, then begins to rise later (until it reaches the latest sunrise time). The Sun also sets later as it rises earlier (sets earlier as it rises later).
- Solstices (至日). The summer solstice marks the longest day, the winter solstice marks the shortest day of the year.
- Sun’s Altitude at Noon (正午太阳高度 - 一日中太阳的最大高度). It rises higher to its peak until the summer solstice, then decreases to its trough until the winter solstice.
Annual Motion of the Sun
我们主要关注太阳的日出点在一年当中的变化 (注意：太阳总在东方升起！)：
- rises to the northeast until it reaches its northernmost point on the summer solstice.
- rises farther south.
- rises exactly in the east on the autumnal equinox (秋分).
- rises to the southeast until it reaches its southernmost point on the winter solstice.
- shifts back north.
- rises exactly in the east again on the vernal equinox (春分).
日出点变化的频率：
- 越往北 (只考虑北半球)，日出位置的变化越明显
- The shift is rapid around equinoxes, moving about 1° per day, but slows down near the solstices.
The Seasons
- 冬至日的文化意义：为接下来难过的几个月储存粮食；庆祝白天从此开始变长。
- Tropic of Cancer (北回归线)：太阳在夏至日直射。
- Tropic of Capricorn (南回归线)：太阳在冬至日直射。
Regular But Not Simple
我们的祖先很快发现，天体运动显然遵循着一定规律，但并不简单。太阳东升西落，但日出点与日落点变化莫测；月亮有时在白天也出现，有时在夜晚也不出现，这与白天黑夜分属日月两位神祇管理的神话相矛盾。流星，彗星与日食等「怪异」的天体现象，更使人类对星空的「永恒」产生了怀疑。
为何天体运动的规律如此复杂？创世者是否在其背后隐藏了某种讯息？这样「安排」的意义是什么？太阳与月亮是上帝为了我们的方便而创造的吗？说到底，我们在星空中究竟位于何处 What was our place in the Universe？