Why do astronomers never put a scale on their photographs?

Question

Why do astronomers never put a scale on their photographs? I have been looking at images of the Bird nebula, a collision of three galaxies, but in none of the dozen or so that I have found, nor in the accompanying text, is there any scale to show how much (or how little) sky this represents. No cartographer would omit a scale of distance from, say, an isolated Pacific island, but very very seldom do I see an arc-second, or whatever is appropriate, scale on a photograph of the sky. This omission is not just for this one image, amazingly it is true for every (well 99.99...% of them) astronomical picture I look at.The area covered by the Bird must be very small as the picture came from a clever analysis of data from Hubble and a new South African telescope, but it would greatly enrich the wonder of this achievement if we were told just how tiny it appears in the sky.I have posted this as a question, I would really like to see, and sign up to, a petition to demand that astrophotographers correct this strange policy.

Answer 1

The short answer to this question is quiet simple: Scaling celestial bodies such as the nebula you mentioned or 3 galaxies would be irrelevant to the average person. Most people think a light-year is a measurement of time, even though it is distance. People would not comprehend something being an "Astronomical Unit" or a "Solar Mass". So why scale it?

It terms of scaling how much of the sky a particular object covers; well for most its 0%. Light pollution keeps most people from even being able to see 25-100 stars at night. We certainly cant see nebula or other celestial bodies.