postgis - How to measure length of line accurately?

In postgis 1.5 for the below given query the answer is 1540651.62674101 meters ,

SELECT ST_Length(ST_GeomFromText('LINESTRING(77.83042478941326 
9.98463896136159,78.03469506809812 23.90398909552571 )',4326),true);

but in google earth the same line gives 1538923 meters in its properties, around 0.1% error between the two readings.

Which one is accurate, if Google earth reading is accurate, how to get it in postgis1.5 ...

any idea...

please help.