When observing phenomena like an eclipse in an eclipsing binary or an exoplanet transit, (amateur) astronomers often schedule their observations around the time of the (mid-)eclipse or transit event. This requires some a priori knowledge about the timing of the event. Phoranso provides a convenient Ephemeris calculator to determine the Calendar date and (geocentric) Julian date of such events, within a user-defined time interval.


Let's walk through an example of using the Ephemeris calculator to calculate the mid-eclipse timings for the star V Sge from Jul 1st till Jul 5th, 2026.


  1. Select Ephemeris calculator from the Tools menu to open the Ephemeris calculator. 

  2. Enter V Sge in the Object name field. The Used names field recalls previously entered Object names of successful ephemeris calculations. You can clear the entries with the Clear button.

  3. Enter the reference epoch as 2,432,407.5308 in the Epoch (JD) field, and the orbital period as 0.5141998 in the E field. Leave the E^2 value as 0 since we don't have information about secondary terms. The above values can be found in literature.

  4. Set the start date to 7/1/2026 and the start time to 0h00m00s. Set the end date to 7/4/2026 and the end date to 23h59m59s.

  5. Click the Calculate button. This will generate a list of all (mid) eclipse times, displaying the Calendar date (UTC), time and (geocentric) Julian date for each event. 


  1. Optionally, click Export to file to export the calculations to a text file.