Caption: The horizontal coordinate system illustrated by an applet from NAAP applet: The Observer.

EOF

The horizontal coordinate system has its origin is wherever you, the observer, are on the surface of the Earth.

There are some features to describe.

The Earth is an infinite plane from your perspective that cuts the celestial sphere in a great circle called the horizon.

The cardinal directions (north, south, east, and west) are on the horizon.

Zenith is the point on the sky directly above the observation point. It's on the vertical from the observer.

Nadir is the opposite point on the sky which you usually can't see since you-know-what is in the way.

The meridian is a great circle that passes through due north, Zenith, due south, and Nadir.

In the horizontal coordinate system, one locates an astronomical object using altitude (the angle from the horizon along a great circle through the zenith) and azimuth (an angle along the horizon measured east from due north).

Credit/Permission: © Astronomy Education at the University of Nebraska-Lincoln / Nebraska Astronomy Applet Project (NAAP), before or circa 2014 / Non-profit education use permitted.
Applet link: NAAP applet: The Observer.
Local file: local link: naap_observer.html.
File: Applet file: naap_observer.html.