Find Closest Location from longitude and latitude within Sql database using Linq

FindClosesLocation.cs

var constValue = 57.2957795130823D

var constValue2 = 3958.75586574D;

var searchWithin = 20;

double latitude = ConversionHelper.SafeConvertToDoubleCultureInd(Latitude, 0),
                    longitude = ConversionHelper.SafeConvertToDoubleCultureInd(Longitude, 0);
var loc = (from l in DB.locations
            let temp = Math.Sin(Convert.ToDouble(l.Latitude) / constValue) 
            *  Math.Sin(Convert.ToDouble(latitude) / constValue) 
            +  Math.Cos(Convert.ToDouble(l.Latitude) / constValue) 
            *  Math.Cos(Convert.ToDouble(latitude) / constValue) 
            *  Math.Cos((Convert.ToDouble(longitude) / constValue) 
            - (Convert.ToDouble(l.Longitude) / constValue))
                    let calMiles = (constValue2 * Math.Acos(temp > 1 ? 1 : (temp < -1 ? -1 : temp)))
                    where (l.Latitude > 0 && l.Longitude > 0)
                    orderby calMiles
                    select new location
                      {
                         Name = l.name
                      });
                      return loc .ToList();

what constValue? why u need that?