Yes, ha is a Scrabble word!
...and is worth 5 points in Scrabble, and 4 points in Words with Friends
ha
Noun
1. (astronomy) the angular distance of a celestial point measured westward along the celestial equator from the zenith crossing; the right ascension for an observer at a particular location and time of day
What Scrabble words can I make with the letters in ha?
2 Letter Words