Julian Day is an Android app that simplifies time computations by using the Julian day system. This system is used in astronomy and provides a single system of dates that can be used when working with different calendars. The app allows you to convert any date to its equivalent Julian day number and vice versa, making it easy to calculate time ranges and roll dates.

The Julian day number is the integer number of days that have elapsed since noon Greenwich Mean Time Monday, January 1, 4713 BC. The Julian Date is the number of days (with decimal fraction of the day) that have elapsed since the same epoch. The app provides an easy-to-use interface for converting dates to Julian day numbers and vice versa.

Using Julian Day is useful for reference, computations, and conversions. It allows you to calculate the time between any two dates in history by simple subtraction. With its simple calendar system, Julian Day makes time computations much simpler and more accessible.