April 30

1006 – Supernova "SN 1006," the brightest supernova in recorded history, appears in the constellation Lupus.
1897 – J.J. Thomson of the Cavendish Laboratory announces his discovery of the electron as a subatomic particle at a lecture at the Royal Institution in London.

2403 – Patricia DeLacroix is assigned as commanding officer of the USS Philadelphia, FF-6053.