He is deeply involved in the study of the meridian system.

We use this coordinate system to locate the position of an object.

The ecosystem of this lake is very fragile.

In physics, the inertial frame of reference is a very important concept.

This system is very complex.

Radio astronomy plays a very important role in understanding the universe.

He used a radar to search for the ship.

He likes to take a walk in the park at dusk.

He is spending a lot of time on experimental research.

She started doing yoga to balance her autonomic nervous system.