Here’s a little piece of post-Y2K calendar trivia for you. Since the 1950s, astronomers and geophysicists have used Julian dates to track time in continuous, absolute terms, without bothersome seasons, leap years, or man-made conventions. Julian dates associate a date with the number of days elapsed since January 1 of the same year. (For example, Jan. 2, 2000, has the value of 2.)

Excel doesn’t have a built-in option to convert dates to Julian time, but you can use this shortcut to convert today’s date to the Julian format:
Just type this equation into any cell in your worksheet:

=VALUE(RIGHT(YEAR(TODAY()),2)&TEXT(TODAY()-DATE(YEAR(TODAY())-1,12,31),"000"))

Now, you’ll need to format this value to display five digits.

1. Right-click in the cell that contains the value and select Format Cells.
2. On the Number tab, choose Custom from the Category list box.
3. In the Type text box, enter 00000.
4. Click OK.