clipping is where the natural curve of the histogram is cut off or "clipped".
An image can be black clipped, usually done to reduce sky background noise or gradients.. sometimes done to create an inky black background... which-ever reason, its not the way to go..
Just as it can be black clipped, an image can be white clipped also, this is what has happened in your images, where instead of Alnitak appearing as a star in your image, its a stark white spot.. This can be caused by over-exposure, or over stretching the data to try to reveal more nebulosity.
Jase can likely correct my terminology here, as im fairly new to the game myself.. but generally speaking, Clipping the histogram is bad, for any reason.. There is almost always another way around it, whether it be taking some shorter subs and masking them in, creating masks and adjusting levels/curves for certain problem areas or other, more technical ways which again, Jase can describe better than I can..
All that being said, like I mentioned earlier, thats a great set of images for one night... I'd be very pleased...
Ps.. I want your camera!! GIMME GIMME GIMME GIMMME GIMMMMEEE!!!
Alex.