Stars consist mainly of hydrogen and which other gas?

The story behind the answer

Helium is correct because stars are mostly hydrogen and helium. In a star’s core, hydrogen nuclei fuse to form helium, releasing enormous energy—the very process that makes stars shine. Spectroscopy of starlight shows strong hydrogen and helium lines, while gases like nitrogen, oxygen, and argon are present only in tiny traces.

Remember it this way: the universe (and stars) start like the periodic table—H then He. After the Big Bang, about three-quarters of ordinary matter was hydrogen and most of the rest helium; stars largely preserve that mix. Helium even got its name from Helios, the Greek sun god, because it was discovered in the Sun’s spectrum before it was found on Earth. Think “H to He = star power.”