From the time series observations obtained between 2005 and 2019 , we have built eight different light curves . Additionally , we used data published in the literature by Jewitt & Sheppard ( 2002 ) ; Lellouch et al . ( 2002 ) and Hicks et al . ( 2005 ) , thus incorporating three additional light curves to our study from previous years ( figure 1 ) . All the light curves were corrected from light travel time . Because Varuna 's body is assumed to have an ellipsoidal shape ( e.g. , Jewitt & Sheppard 2002;Lellouch et al . 2002 ) , data from each light curve were fitted to a Fourier series m = Σ i [ a i sin(2iπφ ) + b i cos(2iπφ ) ] , where m is the theoretical value of the relative magnitude obtained from the fit , φ is the rotational phase ( calculated as the fractional part of ( JD − JD 0 ) /P , where JD is the Julian Date , JD 0 = 2451957.0 is the initial Julian Date , and P is the rotation period in days ) , and ( a i , b i ) are the coefficients of the Fourier function ( with i = 0 , 1 , 2 , ... ) . In our specific case , we used up to secondorder ( i = 2 ) or up to fourth - order ( i = 4 ) Fourier functions . The second order is the minimum order that allows a double - peaked fit ; however , higher orders take into account small deviations on inhomogeneous objects and can be used to fit light curves that are highly sampled . The 2001The , 2002A , 2011The , 2018 and 2019 light curves were fitted to a fourth - order function , while the remaining light curves were fitted to a second - order Fourier function , because the number of data points in those runs was not large enough to use a higher order . Data were folded using Varuna 's rotation period of 6.343572±0.000006 h , which is obtained using the Lomb periodogram analysis of all our data , in agreement with the previous one reported in Belskaya et al . ( 2006 ) . The peak - to - valley amplitudes ∆m ( amplitudes in the following ) of each light curve are given by the absolute maximum and minimum produced by the fits . Table 1 contains the results from the fit to each light curve , i.e. , the amplitude and the dispersion of the residuals of the Fourier function fit to the observational data . One of the evident results is that the amplitude has changed considerably along these 19 years , with an increase of ∼ 0.13 mag . Online table 2 presents all the relative photometry observations from 2005 to 2019 .