The Mantra
Aum
Bhuh Bhuvah Svah
Tat Savitur Varenyam
Bhargo Devasya Dheemahi
Dhiyo Yo nah Prachodayat
~ The Rig Veda (10:16:3)
"O thou existence Absolute, Creator of the three dimensions, we contemplate upon thy divine light. May He stimulate our intellect and bestow upon us true knowledge."
Or simply,
"O Divine mother, our hearts are filled with darkness. Please make this darkness distant from us and promote illumination within us."
Let us take each word of the Gayatri Mantra and try to understand its inherent meaning.
The First Word Om (Aum)
It is also called Pranav because its sound emanates from the Prana (vital vibration), which feels the Universe. The scripture says "Aum Iti Ek Akshara Brahman" (Aum that one syllable is Brahman).
When you pronounce AUM:
A - emerges from the throat, originating in the region of the navel
U - rolls over the tongue
M - ends on the lips
A - waking, U - dreaming, M - sleeping
It is the sum and substance of all the words that can emanate from the human throat. It is the primordial fundamental sound symbolic of the Universal Absolute.
The "Vyahrities":Bhuh, Bhuvah & Svah
The above three words of the Gayatri, which literally means "past," "present," and "future," are called Vyahrities. Vyahriti is that which gives knowledge of entire cosmos or "ahriti". The scripture says: "Visheshenh Aahritih sarva viraat, praahlaanam prakashokaranh vyahritih". Thus, by uttering these three words, the chanter contemplates the Glory of God that illumines the three worlds or the regions of experience.
The Remaining Words
Tat simply means "that" because it defies description through speech or language, the "Ultimate Reality."
Savitur means "Divine Sun" (the ultimate light of wisdom) not to be confused with the ordinary sun.
Varenium means "adore"
Bhargo means "illumination"
Devasya means "Divine Grace"
Dheemahi means "we contemplate"
Dhi means intellect
Yo means "who"
Nah means "ours"
Prachodayat means "requesting / urging / praying"
The last five words constitute the prayer for final liberation through the awakening of our true intelligence.