This image, taken by NASA/ESA’s Hubble Space Telescope, shows many spiral galaxies: The large, prominent spiral galaxy at the right of the image is NGC 1356; Surrounding it are two apparently smaller spiral galaxies, LEDA 467699 (top) and LEDA 95415 (very close to the left), respectively; and finally IC 1947 is on the left side of the image.

This image is a really interesting example of how difficult it is to tell whether two galaxies are actually close to each other, or whether they are just visible from our vantage point on Earth. A quick look at this image will make you think that NGC 1356, LEDA 467699, and LEDA 95415 are close companions, while IC 1947 is more distant. But we must remember that 2D images like this only show angular resolution, that is, how objects are distributed across the sphere of the night sky. What they cannot represent is the distance of objects from Earth.

For example, although NGC 1356 and LEDA 95415 certainly appear close enough to interact, the former is about 550 million light-years away from Earth, while the latter is about 840 million light-years away, a whopping almost 300 million light-years away. -years distance between them years This also means that LEDA 95415 is not as small as NGC 1356 appears to be.

On the other hand, although NGC 1356 and IC 1947 appear to be separated by a relative gulf in this image, IC 1947 is only about 500 million light-years away from Earth. As seen in this image, the angular distance between them is less than 400,000 light-years; so in three dimensions they are actually much closer neighbors than NGC 1356 and LEDA 95415!