What is the source for all the widely-diverging times for Tzais HaKochavim, and what was the custom in earlier generations? Why do some luchos have multiple times for Alos HaShachar? What are “degrees”? When is Misheyakir? Can sunrise be calculated to the precise second? Can I rely on the listed time for Shkiah on Erev Shabbos? All of these issues, and many more, are addressed in this groundbreaking book that is designed to accommodate both the beginner as well as those who are already well-versed in this topic.