同时遮蔽 meaning in English

simultaneous masking

In this graph , the galactic plane is horizontal and we ignore the distances . note that the gas and dust in our galaxy not only block the stars in our galaxy , but also the galaxies far away . taking this into consideration , the distribution of the galaxies is fairly uniform
图中中间的水平线标示出银河系平面，银河系的气体尘埃除了掩盖了背景星光，亦同时遮蔽了遥远的星系，撇除了这个因素，我们会发觉星系在天空的分布是颇为平均的。