Here, we analyzed magnetic elements of the solar active regions (ARs) observed in the line-of-sight magnetograms (the 6173 \AA~Fe \small{I} line) recorded with the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI). The Yet Another Feature Tracking Algorithm (\textsf{YAFTA}) was employed to extract the statistical properties of these features (\textit{e.g.} filling factor, magnetic flux, and lifetime) within the areas of $180{\small^{\prime\prime}} \times 180{\small^{\prime\prime}}$ inside the flaring AR (NOAA 12443) and the non-flaring AR (NOAA 12446) for 3 to 5 November 2015 and for 4 to 6 November 2015, respectively. The mean filling factor of polarities was obtained to be about 0.49 for the flaring AR; this value was 0.08 for the non-flaring AR. Time series of the filling factors of the negative and positive polarities for the flaring AR showed anti-correlation (with the Pearson value of -0.80); while for the non-flaring AR, there was the strong positive correlation (with the Pearson value of 0.95). A power-law function was fitted to the frequency distributions of flux ($F$), size ($S$), and lifetime ($T$). Power exponents of the distributions of flux, size, and lifetime for the flaring AR were obtained to be about -2.36, -3.11, and -1.70, respectively; these values of exponents for the non-flaring AR were found to be about -2.53, -3.42, and -1.61, respectively. ...

In order to check the performance of the Gaia satellite when detecting double stars, we attempted to discover a photocenter shift affecting Gaia's second data release (Gaia DR2). We analyzed data of bona-fide double stars from Double and Multiple System Annex catalog and matched them with the Gaia DR2 catalog. We tried to derive a relationship between measurements of visual magnitude and signs of binarity based on parallaxes and proper motions. A comprehensive study of parallaxes indicates the presence of the photocenter shift effect. Due to the proper motion two-dimensional nature, we conducted only a simply study which implies that a real photocenter shift may affect double stars appearing in the Gaia DR2 catalog as single sources.