Asked by David Kane
If we were able to walk through a nebula, you would barely notice it. Despite appearances, nebulae have a density millions of times lower than that of the air around us.
The reason they appear solid when we observe them on Earth is because we are seeing the big picture. As we view these structures we’re looking at objects millions of kilometres across and with a similar depth. This results in us seeing an object standing out against the featureless backdrop of space. If we found ourselves inside we would appear to be surrounded by nothing apart from a brightly coloured region of space.
Answered by Sophie Allan from the National Space Centre
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