 Hendrik C. van de Hulst

Hendrik C. van de Hulst was a Dutch astronomer, known primarily for his contributions to the field of astrophysics, particularly in relation to the study of interstellar medium and the physics of the hydrogen line. He is well-known for predicting the existence of the 21-centimeter hydrogen line, which is a spectral line created by the hyperfine transition in the ground state of neutral hydrogen.