Yep, however much I meditate on the emptiness of space within a galaxy I still struggle to imagine a field of a 100 billion stars merging with another without the odd bump.

Perhaps the key is to recall how big and voluminous galaxies are: if one were a plate in front of you another might be a plate on just the other side of the room (compare with stars where the other plate would be in the next county).

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Yonder is Dubhe seen on Earth tonight as it was in the days of Grover Cleveland's presidency whereas this way is Deneb seen as it was in the lifetime of Muhammed . If one somehow travelled to Deneb at very close to c then whenever you looked back you'd measure Earth as closer to you than the distance you would simultaneously measure between Earth and Dubhe.