Where "long" may be measured in anything from hours to months.

The Hubble Ultra Deep Field image (a follow-up to the original 1995 Deep Field image of an "empty" region of sky), has a total exposure time of just under 1 million seconds (11 days), with single channel exposures of a minimum of about 1.5 days.

This somewhat exceeds the duration and light-collecting capabilities of a human observer.

https://en.wikipedia.org/wiki/Hubble_Ultra-Deep_Field

Though granted, such prolonged exposures aren't necessary for the nearer observations (many within the solar system) included in the article here.

Especially the Orion Nebula. I see the picture on the left and think oh yeah that’s almost exactly what I see with my scope. Then on the right it’s some crazy photoshopped (playing with channels) long exposure.

Curious, what is the book?

"Astronomía" in Spanish, by José Comas Solá. It was a gift for me, almost 50 years ago. I think it was a little dated already.