On this day in 1918 - November 19th - Dutch astronomer and mathematician Hendrik C. van de Hulst was born.
He predicted the existence of the 21 cm hyperfine line of neutral interstellar hydrogen. When it was discovered, he worked with Jan Oort and others to use radio astronomy to map out the neutral hydrogen in our galaxy, which first revealed its spiral structure.
We take forum safety very seriously here at BellaOnline. Please be sure to read through our Forum Guidelines. Let us know if you have any questions or comments!