### Common Terms

Celestial Dome

• That portion of the sky that would be visible if all human-made structures were removed and there was an unobstructed view of the horizon in all directions from the observation site.

Height (of the cloud base)

• The vertical distance from the ground at the observation point to the base of the cloud. Often referred to as height above ground level (AGL). Cloud heights are expressed in feet.

Elevation

• The vertical distance to a point on the surface of the earth, measured from mean sea level.

Altitude

• The vertical distance of a point measured from mean sea level. Commonly refers to the height of an aircraft above mean sea level (AMSL).

Vertical Extent (of the cloud)

• Vertical distance between the cloud base and the cloud top.