阅读下面这首元诗，然后回答问题。
寒夜作
揭傒斯
疏星冻霜空，流月湿林薄。
虚馆人不眠，时闻一叶落。
（1）诗人作此诗的时令是何时？首句的“冻”字可否用“映”“点”“著”等替换，试作简要分析。
答：                                                                                                                                                                                                        
                                                                                                                                                                                                            
（2）全诗最精彩的是哪一句？试作简要赏析。
答：