Here at Astronomy magazine, we definitely want you to be prepared for the total solar eclipse that will sweep across the United States on August 21, 2017. So that we’re all speaking the same language, we’ve prepared a brief glossary, which includes a few illustrations from past issues.
altitude — the angular height of a point or celestial object above the horizon measured from 0° (on the horizon) to 90° (at the zenith).
angular diameter — the apparent size of a celestial object, measured in degrees, minutes, and/or seconds, as seen from Earth; for example, the average angular size of the Sun and the Moon, as seen from Earth, is 31 arcminutes, or 0.52°.
angular distance — the distance between two celestial bodies expressed in degrees, minutes, and/or seconds of arc.
aphelion — the position of an object in solar orbit when it lies farthest from the Sun.