1. Select FALC (Harris) in the Period analysis menu of the aligned ObsWin to display the Period determination box. 


    • The default Base time in Peranso is Days, which is typical for variable star work. Asteroid period calculations are usually expressed in Hours. Select Hours. 

    • The Unit section allows to select between time based or frequency based calculations. We select Time.

    • We know from a visual inspection of the light curve that there might be a periodicity of about 23.3 hours. Let's enter a wide search Range going from 5 hours to 25 hours with 2500 steps.

    • The Nbr harmonics field defines the number of harmonic orders to be used in the Fourier analysis. If you have sufficient observations (25 or more) that cover a good portion of the light curve, a good starting value is 4. If coverage of the light curve is sparse, e.g., due to large gaps, then use a lower value such as 2. We use 4 for now.

    • Finally, you can specify a Default MagError value. That will be applied during the FALC period analysis to all observations that have no explicit Brightness error defined. Let's use the default value of 0.006 mag.

Click Apply to start the FALC calculation.  


  1. This creates a Period Window showing a dominant period which (somewhat suprisingly) is not at 23.3 hours but at 10.320 hours, so about half of the period we expected from visual inspection. The explanation for this difference is rather simple: the observer captured a maximum each night around the same time, but missing each time an in-between maximum (which occured during his daytime).

    We now have a much more precise value and are ready to narrow down the search range, so close the Period Window and let's revisit the Period determination box. We modify the range Start value to 8.5 hours and the End value to 11 hours. We keep all other values and press Apply. This creates the below Period Window.



  2. The refined dominant period has a value of 10.319 hours, which is in excellent agreement with the literature value mentioned in the introduction of this Tutorial. Click on the Info button in the toolbar of the PerWin to bring up the Info box. You will see that the dominant period has a period error of 0.002h.

Remark : the FALC period error is calculated following the algorithm provided by Alan Harris (JPL). It is different from the regular period error calculation method used by Peranso, which is based on a method by Schwarzenberg-Czerny.  


  1. Finally, create a Spectral Window (explained in Tutorial 2) to confirm that the period found in this step is not an artifact of the observing rate.