The cause of that explosion or shock was not observed visually.
The fact that a visually observed impact between two bodies in the physical world is normally associated with a particular sound has to be learned.
Due to its low surface brightness, it is a very difficult object when observed visually.
The pair was also observed visually by Coteau in 1973.
It can be observed visually, using a 30-35 cm or bigger telescope under a very dark sky.
It can be observed visually as a "red concrete cubicle".
The galaxies on the list can be observed visually and do not require special photographic or imaging equipment.
A navigating officer on one of the transports visually observed the American force minutes later.
"The only way we can give a person a ticket for littering is if we visually observe them in the act," he said.
The explosions were not visually observed due to thick clouds covering the volcano's summit.
