Every year, China's rail system is seized by Chunyun (春运), the mad rush to get home in time for the Chinese New Year (also called Spring Festival). For millions of rural migrants on the country's factory floors and construction sites, this is the one chance to see family all year long. Chunyun begins about two weeks before Spring Festival and lasts for almost a month after; it is a wave of humanity whose participants exceed China's total population in number [zh]. The lines to buy train tickets can truly reach epic proportions. This year, Spring Festival falls on February 10. The race is about to begin.
You cannot really see the Great Wall from space, by the way.