One of the more philosophical concepts that astronomers have to deal with on an everyday basis is the commingling of space and time in astronomical images.
The underlying idea is straightforward. The speed of light is finite. Light from a star or nebula or galaxy takes a measurable amount of time to cross the space between it and us. Hence, the light we see now left that object at some previous time. We view astronomical objects as they were in the past. As I like to say, looking out in space is also looking back in time.
The implications of this maxim are considerable, especially in dealing with the deep field images from Hubble like the one accompanying this article. Such images contain a wonderful assortment of galaxies, with a few stars here and there. Each object is at a different position in space, both in the two-dimensional sense of a different position within the image and in the three-dimensional sense of being at a different distance from Earth. Further, objects at different distances are seen at different times in the past. Hence, astronomers must examine these deep field images in four-dimensional space-time.
Tackling the expanse of space ...