"An historic"

"An historic" is incorrect. Here are the rules:

Use "an" before a word that starts with a vowel sound:

an apple
an egg
an icicle
an orange

Use "a" otherwise.

Some of these words start with a vowel sound, and some don't. See if you can tell the difference:

hour
honor
honest
hat
historic
hick
hit of bong water

It's "a historic event." It's not "an historic event."

If you really want to sound sophisticated, though, and insist on the "an," please, at least don't pronounce the "h" sound. "An 'istoric" at least is a proper application of the a/an rule to a defensibly mispronounced word, but "an historic" with the "h" pronounced both sounds weird and violates the a/an rule.