There are three datacrons on the Republic faction planet Tython. All three are quite easy to get to and provide minimal attribute bonuses and one matrix shard. All three are required for the Tython Datacron Master achievement.
The Tython +2 green endurance datacron.
Codex type: Achievement: Datacrons
Codex location: Tython
Codex coordinates:-33, -101
Faction: Republic
Class: Jedi Consular - Jedi Knight - Smuggler - Trooper
Associated Achievement: Tython Datacron Master
The Tython +2 purple mastery datacron.
Codex type: Achievement: Datacrons
Codex location: Tython
Codex coordinates: -641, -70
Faction: Republic
Class: Jedi Consular - Jedi Knight - Smuggler - Trooper
Associated Achievement: Tython Datacron Master
The Republic's Tython blue matrix shard.
Codex type: Achievement: Datacrons
Codex location: Tython
Codex coordinates: -90, 913
Faction: Republic
Class: Jedi Consular - Jedi Knight - Smuggler - Trooper
Associated Achievement: Tython Datacron Master