Glossary of Radio Astronomy Terms
Z
Zenith:
The point on a celestial object that is vertically above the observer. (90 degrees above the observer)
![Zenith](https://public.nrao.edu/wp-content/uploads/2017/08/Zenith-Nadir-Horizon.svg-150x150.png)
Zenith distance:
the angular distance of a celestial body from a zenith
Zero-age main sequence (ZAMS):
The main sequence on the Hertzsprung-Russell diagram as defined by the stars that have yet to go through substantial evolution. (See Hertzsprung-Russell Diagram for more)