The new ephemeris and light curve analysis by synthesizing our mid-eclipse times and the former observations of BF Pav, that is classified as a W UMa-type eclipsing binary, are presented in this study. We also obtain this binary system's period changes using Wilson-Devinney code after five nights of observation utilizing BVRI filters. Our results demonstrate that BF Pav is a contact binary system with a photometric mass ratio 𝑞 = 0.94, and a fillout factor 𝑓 = 13%. We also calculated the distance of BF Pav 𝑑 = 250 ± 27 pc from distance modulus formula, which is in good agreement with the distance obtained from this binary system's parallax in Gaia DR2. From our O-C analysis, we found a continuous period increase at a rate of 0.3086634× 10 𝑑𝑎𝑦/𝑦𝑟 which corresponds to a period increase of 0.266 s 𝑐𝑒𝑛𝑡𝑢𝑟𝑦 . We determined the mass of each component of this binary system using two different methods and compare our results with the former study's results.

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Transit Timing Variation (TTV) is a powerful method to study the dynamics of multiple transiting planetary systems. We examined the TTV of four planetary systems: WASP-12b, WASP-33b, WASP-36b, and WASP-46b. The purpose of this work is to refine the reference ephemeris of these four systems and to draw inferences on any apparent variability of the transits' periodicity. We used the light curves of these systems from the Transiting light Exoplanet Survey Satellite (TESS) observations and some ground-based telescopes. We modeled these light curves to measure the transit times using Exofast. We plotted their TTV diagrams built from our obtained midtransit times and those available in the literature. Our MCMC analysis of these timings enabled us to refined the transit ephemeris of the four systems. We found an apparent variation of the orbital period, 𝑝̇= −24 ± 2 𝑚𝑠 𝑦𝑟 for WASP-12b and 𝑄 * = (2.16 ± 0.35) × 10 for the tidal quality parameter of its host star. We realized that the orbital period is increasing in the WASP-46b system, so its star magnetic activity is a stronger model than orbital decay for period variation of this system. We obtained ∆𝑃 = 7.37 ± 8.64 𝑚𝑠 during 10 years for WASP-36b; It indicates that orbital decay may be present in this system. But since there is no obvious quadratic trend in its TTV diagram, variations are likely due to wrong linear ephemeris that increased over 10 years.