This element is consumed in the CNO cycle and proton-proton chain. For 10 points each:
[10e] Name this most abundant element in the universe. A heavier isotope of this element is deuterium.
ANSWER: hydrogen [or H]
[10h] Transitions in the hyperfine structure of hydrogen create this spectral line, named for its wavelength. Radio waves in this feature are used to observe properties of galaxies.
ANSWER: 21 centimeter line [or 21 cm; reject equivalents of “21 centimeters”, such as “0.21 meters”]
[10m] Radio waves in the 21 centimeter line, unlike visible light, can also pass through this substance undeterred. The interstellar medium consists of gas, cosmic rays, and this substance.
ANSWER: cosmic dust [or extraterrestrial dust or interstellar dust or space dust or star dust]
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