Observing dark nebulae is difficult.

This problem is very difficult.

Observing a nebula is a wonderful experience that makes you feel the mystery of the universe.

He was observing the behavior of the birds.

He was observing the behavior of birds.

He was able to find the way in the darkness.

His heart was full of darkness.

He committed another crime while on probation.

I often go birdwatching in the park on weekends.

The Horsehead Nebula is one of the celestial bodies that symbolize the beauty of the universe.