Help W/ Distance Calculation Query

I'm trying to run a dyncamic query that returns all records within a specific distance of a certain point. The longitude and latitude of each record is stored in the database. The query is constructed from two dynamic variables $StartLatitude and $StartLongitude with represent the starting point.

SELECT UserID, ACOS(SIN($StartLatitude * PI() / 180) * SIN(Latitude * PI() / 180) + COS($StartLatitude * PI() / 180) * COS(Latitude * PI() / 180) * COS(($StartLongitude - Longitude) * PI() / 180)) * 180 / PI() * 60 * 1.1515 AS Distance
FROM HPN_Painters
HAVING (Distance <= 150)

It runs fine until I add the 'HAVING (Distance <= 150)' clause, in which I recieve the error: Invalid column name 'Distance' It seems that Distance cannot be referenced in the HAVING clause.