Those of us who are properly educated know when to use “a” and when to use “an”.  Usually, “an” is used before a word starting with a vowel. However, there is one quirk in that and perhaps even more.

When speaking/writing about UFO’s, the proper way is to say/write “a” UFO, not “an” UFO, but if saying/writing it out, the proper way is to write/say “an” unidentified flying object.

Both UFO and unidentified flying object start with a vowel, but whether to use “a” or “an” depends on whether you write it out or abbreviate it.

Strange, but true.