a historic / an historic
Which article to use before historic and historical.
Use a historic and a historical. Both words are pronounced with an audible h, so they take a, not an. The same rule covers a hotel, a hypothesis, and a historian.
Examples
UseThe moon landing was a historic event.
UseShe wrote a historical novel set in 1863.
AvoidThe moon landing was an historic event.
An historic is an older form that survives in some British and ceremonial prose. It is not the default in current English. For the general rule that governs this pair, see a / an.