Edit: from ground telescopes
In: Earth Science
From ground telescopes or satelites?
There are two components to taking those kinds of images.
1) nebulae are pretty dim, so you need to collect as much of that faint light as you can. This means using the widest lens you can and leaving the shutter open for a long time.
2) the Earth is rotating, so any astronomical object appears to move in an arc across the sky. You have to have a camera that tracks that path exactly so the object remains fixed in place from the cameras point of view.
In practice, this means hooking a camera up to a telescope and programming a motor controller to slowly change the direction of the telescope so the object remains in view. You then open the shutter and start collecting light. Depending on how faint the object is, you might leave the shutter open all night, ending an hour or so before dawn. (As dawn approaches, sky glow from the Sun lighting up the atmosphere above you degrades the view of the object you are recording)
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