When talking astronomy pictures, it’s difficult to say which pictures are ”real” and which ones are not. A great deal is obviously just computer generated or hand drawn, but the ones I post as part of the Beautiful Cosmos blog series all have some degree of validity to them. The first problem that crops up is simply that as soon as you get a photo from some distance (from a good telescope or a probe) the light you catch is not just visible. Most astronomy pictures try to represent the many variations of colours that the human eye simply isn’t capable to capture or comprehend.
A problem is that we can’t really estimate the exact colours of nebulae, supernovae and galaxies when they are basically impossible to see on close-up without… you know, dying. So the basic answer to how for example a nebula would look from just a couple of light years is… you wouldn’t see it. It’s surrounded by clouds of dust blocking vision and – again – killing you. The best the astronomers can do is a rough estimate.
When it comes to planets and moons, it’s a little different. Almost all pictures of moons (including our) and the planets (including Earth) that you’ll see, including ones I post, are composites of several different pictures, sometimes just a couple and sometimes several dozens. That doesn’t make it the less real, it just allows for much higher precision than if you took a photo of the entire planet at the same time. The end result is basically how it’d look in real life. To me, this is real enough.
A great deal of high-detail photos that include several objects (such as a planet and its moon(s)) are ”fake” in that they are composited of different pictures. All photos you have ever seen of several planets (close up) at the same time are totally fake. Planets simple aren’t close enough, and photographing two planets in our solar system together is akin to photographing two flies on opposite sides of a football field. Obviously it can be done – planets like Venus, Jupiter, Uranus and Mars can all be viewed simultaneously on Earth’s night sky – but they won’t be in such high detail.
This picture, of Jupiter and it’s moon Io, is both real and fake. It’s all real, but the Jupiter part is made up of three composites, and the Io part is taken at a different time and then added. Still, they seem to fit in proportion, and from the right angle this is just as awesome as it would look. Read more about the authenticity of this particular picture on the Bad Astronomer Phil Plait’s blog.