The six main subject areas of phonetics, ritualistic knowledge, grammar, exegetics, metrics and astronomy are called

The six fields of phonetics, ritual, grammar, etymology, metrics and astronomy together form the Vedangas.

The Darshanas are the six schools of philosophy, not these auxiliary studies.

The Pitakas are the three baskets of Buddhist scripture, unrelated to Vedic limbs.

The Upanishads are the philosophical close of the Vedas, not a list of subjects.

The Vedangas were studied as aids to understand and use the Vedas correctly.

Their names are Shiksha, Kalpa, Vyakarana, Nirukta, Chhanda and Jyotisha.