What's the difference between the Julian and the Julian Ephemeris Day? I'm making a code where I calculate the sun position in a given time. But I also want to learn astronomy with it. I'm following a .pdf to make the program, and in this .pdf it says 


  The Julian Day (JD) is calculated using UT and the Julian Ephemeris
  Day (JDE) is calculated using TT.


Is it the only difference?
Is it the only difference?


By definition, yes. It's important to keep in mind that the difference between TT and UT (UT1) is not constant.