Figure 1: The count rate recorded by a neutron monitor is an indicator of the Galactic cosmic ray flux, which undergoes "solar modulation" related to solar activity [1-3]. As solar activity increases (shown in the top panel, Source: WDC-SILSO Royal Observatory of Belgium, Brussels), the pressure-corrected count rate recorded by the neutron monitor in Thule decreases (bottom panel, Source: Bartol Research Institute, University of Delaware, USA). The solar magnetic polarity reversal can be observed as the polarity shifts between positive (represented by A > 0) and negative (represented by A < 0) values. This work presents observations for the periods 1994-2007 and 2019-2020, as indicated by horizontal bars between the two panels.

In this work, we investigate the physical properties of galaxies in Abell 2142 using photometric and spectroscopic data from the Sloan Digital Sky Survey (SDSS). The sample was selected by two criteria: redshift of 0.0781 ⩽ z ⩽ 0.1038 and the location within a radius of 100 arcminutes from the cluster centre. We found that the sample distributes into 2 groups, a foreground filament galaxies with z ⩽ 0.085 and the cluster members with z > 0.085. The relation between apparent magnitude in g filter band and u – z colour suggests that we can use the u – z equals 3.2 as a criterion to separate galaxies into blue (u – z ⩽ 3.2) and red (u – z > 3.2) sequence galaxies. Moreover, blue sequence galaxies have higher value of equivalent width of hydrogen alpha corresponding to higher star forming activity than red sequence galaxies. The nearby filament contains higher fraction of star forming galaxies (65%) than the cluster Abell 2142 galaxy members (46%). This could be due to difference of the environmental effect.