Pictures of galaxies, nebulae: which way is up? We are used to viewing pictures of the Earth and the planets with their North Pole pointing towards the upper portion of the photo. But when a space telescope snaps photos of cosmic entities, do they rotate the photo around to get an attractive composition? Is it a subjective rotation, or are there rules? Which way is up?
Images are often presented with (Earth's) North at the top but there is no correct orientation. For example, in this image from the VLT north is 0.1 degrees from the vertical, the sidebar on the image page has details on the position, field of view and orientation.



However, this image from the same telescope has been rotated left 9 degrees, which is likely an artistic decision.



Amateurs also regularly align the cameras on their scopes so that north is up as it can make it easier to diagnose tracking problems. However, it's fairly common to change the camera alignment on the telescope to frame particular targets or groups of targets.

Many classes as astronomical objects, such as elliptical galaxies, irregular galaxies or nebulae don't have a well defined or known axis of rotation, which is why Earth's poles are used as a reference.