A) infrared
B) refracted light
C) spectrum (plural: spectra)
D) ultraviolet (UV)
Answer: A
Explanation: Invisible light that we sense as radiant heat, with longer wavelengths (0.78 microns to 1 mm) and lower frequencies and energies than visible light. In astronomy, it is subdivided into three regions: the near infrared (nearest to visible light) ranges from 0.78 to about 2.5 microns; the mid-infrared spans 2.5 to 50 microns; and the far infrared includes wavelengths from 50 to 1,000 microns. (Although some astronomers place the cutoff at 300 microns.) Water vapor absorbs a significant amount of infrared and the atmosphere itself glows at these wavelengths, but some regions can be observed by telescopes atop mountains or aboard high-altitude aircraft, balloons, or rockets where they are above most of the atmosphere's water vapor.