An Etymological Dictionary of Astronomy and Astrophysics

1. An instrument for measuring the intensity of radiant energy in amounts as small as one millionth of an erg. It uses the change in resistance of a thin conductor caused by the heating effect of the radiation. → actinometer, → photometer, →
   pyrheliometer, → pyrometer,
   radiometer.
   
2. In astronomy, an instrument that measures the amount of radiant energy received from a celestial object.

Etymology (EN): From Gk. bole “stroke, beam of light,” from ballein “to throw” + middle suffix -o- + → -meter..

Etymology (PE): Tafsanj, from taf “heat, warmth; light, brightness,” from tâbidan, “→ radiate,”

• sanj, → -meter.